Vegan For Life
by Jack Norris, RD &
Ginny Messina, MPH, RD
Calcium and Vitamin D
by Jack Norris, RD | Last updated: March 2013
Calcium and Vitamin D for Vegans: Summarized! is an abridged, reader-friendly version of this article.
- Calcium & Vegan Diets: Why the Fuss?
- Animal Protein & Osteoporosis
- What Causes Osteoporosis?
- Research on Vegans
- Dangers of Calcium Supplements
- Calcium Absorption from Plant Foods
- Calcium Tips
- Conclusion on Calcium and Vegan Diets
- Vitamin D
- Vitamin D3 vs. Vitamin D2
- Vitamin D Supplements and Meals
- Vitamin D2 in UV Treated Mushrooms
- Vitamin D in Fortified Foods
While not found in many foods, vitamin D can be made by the action of sunlight (UV rays) on skin. Since about 2005, there has been a controversy in scientific circles about the ideal levels of vitamin D for preventing disease with some researchers suggesting amounts much higher than those recommended by the Institute of Medicine. Regardless of this debate (of which there are more details below), I have encountered many vegans, often from sunny areas such as southern California, who have had extremely low levels of vitamin D. At least five were suffering from fatigue or bone pain that improved upon vitamin D supplementation.
If your arms and face (or the equivalent amount of skin or more) is exposed to the following amounts of midday sun (10 am to 2 pm), without sunscreen, on a day when sunburn is possible (i.e., not winter or cloudy), then you should not need any dietary vitamin D that day:
On all other days, follow these recommendations:
25 mcg (1,000 IU) is more than you can get from fortified foods or multivitamins; amounts that high are only available through vitamin D2-only supplements. Country Life makes one that is commonly available in natural foods stores in the U.S. and is fairly inexpensive. Deva makes one that can be ordered by mail. There is evidence that it can be harder to raise vitamin D levels using vitamin D2, the vegan version of vitamin D, and so we suggest somewhat more than the RDA (as reflected in the table above). More on vitamin D2 vs. D3 below. There is also a vegan version of vitamin D3 made by Vitashine.
|Table 4. U.S. DRI for Calcium|
|0 - 6 mos||200|
|6 - 12 mos||260|
|1 - 3 yrs||700|
|4 - 8 yrs||1000|
|9 - 18 yrs||1300|
|19 - 50 yrs||1000|
|51 - 70 yrs (male)||1000|
|51 - 70 yrs (female)||1200|
|14 - 18 pregnant/lactating||1300|
|19 - 50 pregnant/lactating||1000|
Americans are regularly being urged to consume more calcium in order to prevent osteoporosis. It is practically impossible to meet the recommendations without large amounts of cows' milk, calcium-fortified foods, or supplements.
Enter vegan diets. Because vegans do not eat dairy products, their calcium intakes tend to be low. The Dietitian's Guide to Vegetarian Diets (2004) lists 45 studies that have surveyed vegetarians' calcium intakes in Appendix G. The daily calcium intakes in these studies are about:
- Vegans: 500 - 600 mg
- Lacto-ovo vegetarians: 800 - 900 mg
- Non-vegetarians: 1,000 mg
Only one study included supplements. In it, daily calcium intakes were: 840 mg (vegan males), 720 mg (non-vegetarian males), 710 mg (vegan females), and 855 mg (non-vegetarian females).
As you can see above, the calcium intake of vegans tends to be quite a bit lower than lacto-ovo vegetarians, non-vegetarians, and the DRI. Traditionally, the vegan community has responded to this by saying osteoporosis is a disease of calcium loss from the bones, not a lack of calcium in the diet. This was based on two bits of evidence. The first bit is that ecological studies have shown that the countries with the highest intake of dairy products (northern Europe and the USA) have higher rates of hip fractures than do Asian and African countries where much less milk is consumed. This can be explained by the second bit of evidence which is that studies show that after ingesting animal protein, people urinate large amounts of calcium. Therefore, the thinking goes, calcium intake isn't important for preventing osteoporosis and vegans are protected due to the lack of animal protein in their diets.
Let's examine this evidence.
While it is true that Asian countries have lower rates of hip fractures than do higher dairy-consuming countries, it turns out that hip fracture rates can be misleading. The first prospective cohort study measuring clinically diagnosed vertebral fractures in an Asian population, the Hong Kong Osteoporosis Study, found that while hip fracture rates were lower in Hong Kong than Sweden, vertebral fracture rates were higher (7), as shown in the graph below (or you can click here for an easier version to see):
The authors of the Hong Kong Osteoporosis Study state:
The observed ethnic differences in fracture incidences may be due to the fact that hip fracture risk was affected by fall risk, whereas the risk of vertebral fracture mostly depends on bone strength. Despite the low hip fracture rate in our population, Hong Kong women had a higher prevalence of osteoporosis [technical parenthetical deleted] than US Caucasian women (35.8% vs. 20%, respectively) and a similar prevalence of about 6% in Hong Kong and US Caucasian men.
In other words, at least in this group of people from Hong Kong, the Chinese don't have lower rates of osteoporosis.
Here are some excerpts from a 2009 review of the epidemiological studies on protein and bone health:
Overall, there was very little evidence of a deleterious influence of protein intake on [bone mineral density (BMD)], with most cross-sectional surveys and cohort studies reporting either no influence or a positive influence. Thus, 15 cross-sectional surveys found a statistically significant positive relation between protein intake and at least one BMD site. However, 18 studies found no significant correlation between protein intake and at least one BMD site.
The cohort studies also identified little evidence of any deleterious influence of protein intake on bone. ...[N]o studies showed a significant increase in BMD loss with increased protein intake, and only one study showed a significant decrease in BMD loss with increased animal and total protein intakes."
Overall, the [seven] cohort studies indicated either a benefit or no effect of protein intake on hip fracture relative risk, with only one study reporting a significant increase in risk with increasing animal protein intake and increasing animal to vegetable protein ratio. Three studies found a decreased relative risk of hip fracture with increasing animal, total, and vegetable protein intakes. Two studies found no significant association of animal protein with fracture risk, whereas 2 studies found no association of total protein with fracture risk. Last, 2 studies found no relation between fracture risk and vegetable protein.
As mentioned above, there is a theory that protein increases osteoporosis by increasing a loss of calcium through the urine. The idea is that protein, especially through the sulfur-containing amino acids, increases the acid in the blood which, in turn, gets shuttled to the urine, increasing the renal acid load. In order to neutralize that acid, calcium is used as a buffer and then urinated out with the acid.
There has been an enormous amount of research on protein and bone health and this view of protein causing osteoporosis has been refuted. Here are some of the main points of a 2012 literature review (28) of clinical trails on the subject:
- Many clinical trials show that adding purified proteins to the diet increases calcium excretion through the urine. But when whole foods are eaten, this effect is not strong. And phosphorus, in which meat and dairy are rich, counteracts the increase of calcium in the urine between 40 and 65%.
- High protein diets increase acid excretion in the urine, but this can be handled by the body's acid buffer system without the need for calcium.
- In low-calcium, but not high-calcium diets, higher protein intakes probably increase calcium absorption from the digestive tract causing an increase in calcium excretion in the urine.
- Fruits and vegetables are beneficial to bone health, probably due to their high potassium and magnesium content. This could cause confounding in protein studies because diets high in protein are often low in fruits and vegetables.
- There is some evidence that a beneficial effect of protein on bones is only seen when calcium intake and vitamin D status is adequate.
- Maintenance of adequate bone strength and density with aging is dependent on adequate muscle mass which is dependent on adequate intake of protein.
- An increase in IGF-1 is most likely the mechanism for increased bone health with higher protein intakes.
Although HP [high protein] diets induce an increase in net acid and urinary calcium excretion, they do not seem to be linked to impaired calcium balance and no clinical data support the hypothesis of a detrimental effect of HP diet on bone health, except in the context of inadequate calcium supply.
Another 2009 meta-analysis found that among five well-designed studies measuring calcium balance, net acid excretion was not associated with either decreased calcium balance or a marker of bone deterioration (48).
If animal protein doesn't cause osteoporosis, what does?
Genetics likely play a strong role in osteoporosis, and, possibly related, estrogen levels in women. Among factors that can be controlled by lifestyle and diet, there has been evidence for the following:
- Weight-bearing exercise throughout one's lifetime
- Higher body weight
- Adequate intake of calcium, vitamin D, vitamin K, phosphorus, potassium, magnesium, and boron
- High sodium and caffeine intake
- Too little protein
- Excessive vitamin A (retinol, not beta-carotene)
- Possibly vitamin B12 deficiency
Some background: When calcium levels in the blood drop, parathyroid hormone (PTH) is released. PTH causes calcium to be released from the bones, thus raising the low calcium levels in the blood. Osteoporosis may result from chronically high levels of PTH. The conversion of 25-hydroxyvitamin D to calcitriol is also somewhat regulated by PTH levels (4). Calcitriol increases absorption of calcium and phosphorus (another major component of bones) from the intestines and decreases their excretion in the urine. In so doing, calcium levels in the blood rise and PTH levels drop.
Research has shown that, on average, Americans are getting enough calcium. A 2003 report from the Nurses Health Study showed vitamin D to be more important than calcium intake for preventing hip fractures in postmenopausal women (5). In 2007, a meta-analysis of prospective studies and randomized controlled trials found that calcium intake and calcium supplements were not associated with a lower risk for hip fractures (15).
Taking vitamin B12 might also be important for bone mineral density. Two studies have linked low B12 status in vegetarians to poorer bone health.
A 2009 cross-sectional study from Slovakia compared lacto-ovo vegetarian women to omnivores. They found that the vegetarians' higher homocysteine levels (16.5 vs. 12.5 µmol/l; 78% vs. 45% were elevated) and lower vitamin B12 levels (246 vs. 302 pmol/l; 47% vs. 28% were deficient) were associated with significantly lower bone mineral density in the femur (34). Participants were not allowed to have been taking vitamin or mineral supplements. The researchers did not measure calcium intake or vitamin D status.
Another 2009 cross-sectional study of German omnivores, lacto-ovo vegetarians, and omnivores, and Indian lacto-ovo vegetarians and omnivores found higher markers of bone turnover associated with low vitamin B12 status (34). The findings were no worse for the lacto-ovo vegetarians than the vegans, indicating that poor bone health can start with just moderate B12 deficiency. None of the participants were taking B12, calcium, or vitamin D supplements.
Bone Mineral Density
A number of small, cross-sectional studies have shown vegans to have the same or slightly lower bone mineral density as non-vegans (9-12, 13, 30). These studies were done on vegans who might not have gotten much vitamin D and probably did not make an effort to get the recommended amount of calcium in their diet.
In 2009, researchers from Vietnam and Australia did a meta-analysis looking at the bone mineral density of vegetarians (32). They concluded that "[T]here is a modest effect of vegetarian diets, particularly a vegan diet, on [bone mineral density], but the effect size is unlikely to result in a clinically important increase in fracture risk."
In 2007, the first study looking at vegan bone fracture rates was released (14). The EPIC-Oxford study recruited 57,000 participants, including over 1,000 vegans and almost 10,000 lacto-ovo vegetarians, from 1993 to 2000. They were asked to fill out a questionnaire to measure what they ate. About 5 years after entering the study, they were sent a follow-up questionnaire asking if they had suffered any bone fractures.
After adjusting for age alone, the vegans had a 37% higher fracture rate than meat-eaters. After adjusting for age, smoking, alcohol consumption, body mass, physical activity, marital status, births, and hormone replacement, the vegans still had a 30% higher fracture rate. Meat-eaters, fish-eaters, and lacto-ovo fracture rates did not differ in any of the analyses performed.
When the results were adjusted for calcium intake, the vegans no longer had a higher fracture rate. And among the group of subjects who got at least 525 mg of calcium a day (only 55% of the vegans compared to about 95% of the other diet groups), vegans had the same fracture rates as the other diet groups. The study didn't give the average calcium intake of those vegans, but it was possible to calculate that at a minimum, their average calcium intake was 640 mg.
The authors noted that fracture rates did not correlate with protein or vitamin D intake among the people in this study. A separate analysis in EPIC-Oxford (20) showed that, among all participants (regardless of diet group), calcium intake was related to an increased fracture risk in women (relative risk 1.75 (1.33-2.29) for < 525 mg/day compared to > 1200 mg/day), but not in men.
In 2011, a follow-up (49) of an earlier study on vegan Buddhist nuns (30) was released. After two years, the vertebrae of 88 vegans and 93 omnivores were examined using x-rays. Ten women (five vegans and five omnivores) had sustained a new vertebral fracture after two years; there was no significant difference between the two groups.
Rates of bone mineral density (BMD) change were examined at the lumbar spine and femoral neck with a variety of associations found. Lumbar BMD increased with age, lean body mass, and vegetable fat; and decreased with vegetable protein and steroid use. The authors suggested that the increase in BMD of the lumbar spine was possibly due to osteoarthritis and, therefore, not a healthy phenomena.
As for the femoral neck, BMD increased with both lean and fat body mass; and decreased with age, animal fat, and ratio of animal protein to vegetable protein. This would indicate that animal protein had a negative impact on bone. To make this even a bit more complicated, the food questionnaires used by the researchers indicated that the vegans were only eating an average of 1,093 calories, 36 g of protein, and 360 mg of calcium per day. The estimated energy requirement for women their age and size is about 1,600 calories which indicates that the food intake of the vegans was possibly underestimated by one-third. The non-vegan nuns had intakes of 1,429 calories, 62 g of protein, and 590 mg of calcium per day which seems more likely.
Ten fractures in 181 women in two years seemed high. The rate of vertebral fracture in women over 65 in Hong Kong and Japan is 594/100,000 person-years (30). The person-year fracture rate in this Buddhist nun study works out to be 2,762/100,000. That's obviously quite a bit higher, but it should be noted that the fractures in the Buddhist nun study were determined by giving an x-ray to each subject, rather than reporting a bone break, and would likely find more fractures than the study determining the 594/100,000 rate.
In summary, compared to non-vegetarian Buddhist nuns, vegan nuns had a similar rate of vertebral fractures, but it appears that the rates for both groups were relatively high.
Some research has linked calcium supplements with an increased risk of cardiovascular disease. These studies have mostly found a link in people getting well over the DRI for calcium (more info), and with the effect stronger in smokers. A 2013 study from Sweden found that there was no increased risk up to 1,300 mg of calcium per day, but a significantly increased risk for the group getting ≥ 1,400 mg per day (37). A 2012 study that examined the arteries of participants found no correlation with calcium supplements and calcification of the arteries in amounts up to 3,000 mg per day (58). To be safe, it might be best not to increase calcium intake higher than 1,400 mg per day. People with chronic kidney disease should talk to their physicians about the costs and benefits of calcium supplements.
There is some evidence that taking calcium supplements can increase the risk of kidney stones in people who are genetically susceptible. However, taking calcium supplements with meals can actually reduce the risk of calcium-oxalate kidney stones, the most common form of stone.
As a calcium dose increases, the percentage absorbed decreases. Beyond the size of the dose, the oxalate level in a plant food is the main determinant of how much calcium can be absorbed. See Table 5 for the references and details for the following:
- Studies have shown that calcium in fortified soymilk, bok choy, kale, and mustard greens is absorbed well.
- Based on oxalate levels, the calcium in turnip greens should also be absorbed well.
- Based on oxalate levels, the calcium in collards, broccoli, and watercress should be absorbed moderately well.
- Studies have shown that the calcium in spinach and rhubarb is not absorbed well.
- Based on oxalate levels, the calcium in beet greens should not be absorbed well.
Soy milk should be well-shaken to make sure the calcium has not settled to the bottom of the carton.
|Table 5. Calcium in Selected Plant Foods|
|Cow's milk||1 cup||300|
|Soymilk - fortified||1 cup||200-300|
|Soymilk - fortified||250||21%61||53|
|Soymilk - fortified||40||65%62||26|
|Tofu – prepared with calcium salts (check label)||1/2 cup||120-850|
|Beet greens – raw||1 cup||44||231|
|Bok choy – cabbage, chinese (pak-choi), cooked, boiled, drained, shredded||1/2 cup||79||2063||40%63||32|
|Bok choy – cabbage, chinese (pak-choi), raw, shredded||1 cup||74|
|Broccoli – raw - chopped||1 cup||43||173|
|Broccoli – cooked, boiled, drained - chopped||1/2 cup||31|
|Broccoli – frozen, chopped, cooked, boiled, drained||1/2 cup||30|
|Collards – frozen, chopped, cooked, boiled, drained||1/2 cup||179|
|Collards – cooked, boiled, drained, chopped||1/2 cup||133|
|Collards – raw - chopped||1 cup||52||162|
|Kale – raw - chopped||1 cup||90||13|
|Kale – frozen, cooked, boiled, drained, chopped||1/2 cup||90||40%59||36|
|Kale – cooked, boiled, drained, chopped||1/2 cup||47|
|Mustard greens – frozen, cooked, boiled, drained, chopped||1/2 cup||76||2263||40%63||30|
|Mustard greens – raw, chopped||1 cup||58|
|Mustard greens – cooked, boiled, drained, chopped||1/2 cup||52|
|Rhubarb – frozen, cooked, with sugar||1/2 cup||174||41763||9.263||16|
|Spinach, cooked, boiled, drained, without salt||1/2 cup||122||29160||5.1%60||6|
|Spinach – raw||1 cup||30||291|
|Turnip greens – frozen, cooked, boiled||1/2 cup||125|
|Turnip greens – raw, chopped||1 cup||105||28|
|Turnip greens – cooked, boiled, drained, chopped||1/2 cup||99|
|Watercress – raw, chopped||1 cup||41||105|
|Almonds – dry roasted, whole kernels||1/4 cup||92||21%E, 66||19|
|Hummus – commercial||2 tablespoon||11|
|Navy beans – mature seeds, cooked, boiled||1/2 cup||63|
|Refried beans – canned, vegetarian||1/2 cup||42||17%E, 66||7|
|Tahini – from roasted and toasted sesame seed kernels||1 tablespoon||64||21%E, 66||13|
|ACalcium and oxalate amounts do not match the amounts used in the absorption study servings. Calcium to oxalate ratios in the studies were used to determine the oxalate amounts listed in the table based on the calcium amounts listed in the USDA Nutrient Database for the common serving size.|
- Many non-dairy milks are now fortified with calcium, vitamin D, and/or vitamin B12. Many orange juices are fortified with calcium.
- Calcium supplements can inhibit iron absorption if eaten at the same time. (4).
- In addition to the calcium in the leafy greens listed on the right, leafy greens also contain vitamin K, which is good for bones.
- The Daily Value for calcium on food labels is 1,000 mg. Therefore, if a food label says it has 25% of the daily value, it means it has 250 mg of calcium per serving.
There is no reason to think that vegans are protected from osteoporosis more than other diet groups, and they should strive to meet calcium recommendations. Although it is possible to meet the calcium recommendations by eating greens alone (see chart below), the average vegan probably will not meet recommendations without drinking a glass of fortified drink each day, eating calcium-set tofu, or taking a 250 - 300 mg supplement (in addition to eating an otherwise balanced diet). Although it is important to get enough calcium, do not get more than 1,400 mg of calcium per day.
Traditionally, vitamin D recommendations have been based on how much was required to prevent the most obvious diseases of vitamin D deficiency, rickets and osteomalacia. Recently, some research has indicated that higher vitamin D levels might help prevent fibromyalgia, rheumatoid arthritis, multiple sclerosis, upper respiratory tract infections, premenstrual syndrome, polycystic ovary disease, psoriasis, muscle weakness, lower back pain, diabetes, high blood pressure, and cancer (16), and asthma (43). Vitamin D supplementation might also improve mood (16).
Because of these findings, some researchers have suggested that ideal vitamin D levels in the blood should be between 80 to 100 nmol/l (32 to 40 ng/ml) (16). In 2011, the Institute of Medicine (IOM) released a report in which they reviewed the scientific literature. They increased the RDA for vitamin D from 400 to 600 IU, but they concluded that optimal vitamin D levels are 50 to 125 nmol/l (20 to 50 ng/ml) (35).
In a separate paper, members of the IOM committee said (45):
For outcomes beyond bone health, however, including cancer, cardiovascular disease, diabetes, and autoimmune disorders, the evidence was found to be inconsistent and inconclusive as to causality.
A 2010 review in the Journal of the American Dietetic Association came to similar conclusions about vitamin D and cancer prevention (46); i.e., that the data is too inconsistent to draw conclusions.
Most Americans get vitamin D through sunshine, fortified milk, and fortified margarine. The only significant, natural sources of vitamin D in foods are fatty fish (e.g. cod liver oil, mackerel, salmon, sardines), eggs (if chickens have been fed vitamin D), and mushrooms (if treated with UV rays). The vegan diet contains little, if any, vitamin D without fortified foods or supplements.
Vitamin D appears to be more important for bones in conjunction with lower calcium intakes (typical in most vegan diets) than in diets that have large amounts of calcium (5).
|Table 12. Average Vitamin D Levels in EPIC-Oxford36|
|Adjusted for season and year of blood sample collection and age.|
In EPIC-Oxford, lacto-ovo vegetarians had lower levels of vitamin D than did regular meat-eaters and pesco-vegetarians. Vegans had lower levels than lacto-ovo vegetarians. See Table 12. The differences between the diet groups were statistically significant. However, the vegans' levels of 55.9 nmol/l were not deficient according to the optimal level suggested by the Institute of Medicine of 50 to 125 nmol/l.
Adventist Health Study-2 (2009)
Despite low intakes of vitamin D by vegetarians, Adventist Health Study-2 (AHS2) showed no difference in vitamin D levels between vegetarians and non-vegetarians among people aged 51 to 70 years living in the United States. See Table 11. About 4% of the vegetarians were vegan. Once again, on average, the vegetarians' vitamin D levels were adequate.
The study showed that dietary vitamin D intake was a minor factor in someone's vitamin D status at the levels that vitamin D is normally found in the diet. All groups got between 119 and 165 IU of vitamin D per day (the DRI is 600 IU) from their diet.
|Table 11. Average Vitamin D Levels in Adventist Health Study-221|
|aIncluded lacto-ovo-vegetarians and vegans. | bIncluded semivegetarians (ate meat and fish < 1 time/wk) and pesco-vegetarians (ate meat < 1 time/mo, and fish > 1 time/mo).|
The variable causing the greatest difference in 25(OH)D concentrations was not diet, but ethnicity. This is likely due to people with dark skin needing much longer amounts of time in the sun to produce adequate vitamin D.
For many years, people thought that extra amounts of vitamin D made by the sun during the summer could be stored in the body and used during the winter. But it is important to remember that these days many of us spend very little time in the sun without sunscreen.
On average, it appears that most people, including vegans, are sustaining vitamin D levels over the winter that the Institute of Medicine considers healthy. In some cases, they are not.
For example, in a 2000 experiment, vegans in Finland were not able to maintain healthy levels of vitamin D during the winter (8). A follow-up study found an increase in lumbar spine density in 4 out of the 5 vegans who took 5 µg (200 IU) per day of vitamin D2 for 11 months (3). A dose of 5 µg (200 IU) per day was also required to keep vitamin D levels above 40 nmol/l (16 ng/ml) in Ireland during the winter (27).
It should be noted that the American Academy of Dermatology urges people not to get vitamin D via sunshine because of the increased risk of cancer (38). That said, not all researchers recommend complete avoidance of the sun.
According to Dr. Jacqueline Chan, increasing the surface of the skin exposed to the sun proportionately decreases the amount of time needed in the sun to produce the same amount of vitamin D. The duration of the sun exposure should be no more than about half the amount of time it takes for the skin to turn pink (38). Dr. Chan also says that in order to make vitamin D, "The sun must shine directly on skin without being blocked by sunscreen, glass and most plastics. Glass and most plastics block UVB, the part of the spectrum that converts pro-vitamin D3 but allow passage of UVA which contributes to skin cancer." (38)
An article in USA Today, Your Health: Skin color matters in the vitamin D debate (updated 4/19/2009), quotes vitamin D researcher Dr. Michael Holick as saying:
"Though someone in Boston with pale skin can get adequate vitamin D by exposing their arms and legs to the sun for 10 to 15 minutes twice a week in the summer, someone with the darkest skin might need two hours of exposure each time[.]"
This was the most specific statement I could find by a vitamin D researcher on how much sun a dark-skinned person needs to produce adequate vitamin D. As Holick notes in the article, this much sun is impractical and could cause skin cancer. While dark-skinned people have lower rates of skin cancer than whites, they are more likely to get diagnosed past the time that the cancer can be cured.
It is probably best for dark-skinned people to rely on vitamin D supplements rather than exposing themselves to the sun for more than a few minutes at a time. Monitoring vitamin D levels, if possible, would be ideal for knowing if supplements are needed.
Elderly people need 30 minutes a day of direct sunlight in order to produce adequate vitamin D (23).
A 2009 study from Ireland of people aged 64 years or older showed that 5 mcg (200 IU) per day was needed to keep most of the participants' vitamin D levels above 40 nmol/l (16 ng/ml) over the winter (based on the lower standard deviation; 22).
The abstract of a 1982 study indicates that a daily dose of 11.2 µg (450 IU) of vitamin D2 was able to increase vitamin D levels in elderly subjects (24)
Some tanning beds can produce vitamin D with the type of UV rays they emit, but most do not. Experts generally recommend against using tanning beds to produces vitamin D because of their inefficiency and an increased risk of skin cancer. Click here for more information on tanning beds, vitamin D, and skin cancer.
The Vitamin D Council has partnered with ZRT Labs to make a discounted take-home vitamin D test kit available (for $65 as of April 2010).
There are two types of vitamin D supplements:
- Vitamin D3 - cholecalciferol
- Derived from animals (usually from sheep's wool or fish oil). It is the form of vitamin D produced in the skin when exposed to UV rays.
- There is now a brand of vegan vitamin D3 on the market, manufactured by Vitashine (more info).
- Other companies claim to produce a vegan D3 but none have been verified to my satisfaction or by the UK Vegan Society (more info).
- Vitamin D2 - ergocalciferol
There has been a long-running debate on whether vitamin D3 supplements are more effective than vitamin D2. The research has been trickling in since 1998, and in 2012 a thorough meta-analysis by Tripkovic et al. was published making some things clear (53):
- In large boluses of 50,000 IU or more, vitamin D3 is much more effective than D2 at raising and maintaining vitamin D levels.
- In daily amounts of 1,000 to 4,000 IU per day, vitamin D3 is somewhat better than D2 at raising vitamin D3 levels.
There are some things to consider regarding this research, but first we need some background on vitamin D.
Vitamin D2 and D3 are not biologically active. Once ingested or created in the skin, in order to become biologically active, they have to be converted to the hormone, calcitriol. The first step in this process is for the liver to convert the vitamin into 25-hydroxyvitamin D, also known as 25(OH)D. When we talk about "vitamin D levels" going up or down, we are talking about the 25-hydroxyvitamin D. Then, when the body senses a need for more calcitriol, the kidney converts 25-hydroxyvitamin D into calcitriol.
Throughout this process, the part of vitamin D that distinguishes D2 from D3, also known as the side chain, stays attached to the molecule. So, calcitriol is either calcitriol-D2 or calcitriol-D3, and to our knowledge there is no difference in biological activity. However, there is a theory that once converted into calcitriol and then degraded, the calcitriol-D3 can be retroconverted back into 25-hydroxyvitamin D3, but the D2 version of calcitriol cannot be retroconverted or cannot be at nearly the rate of D3. This could explain why infrequent, large boluses of vitamin D2 quickly disappear from the system – the vitamin D is converted to calcitriol, used, and then degraded without replenishing the 25-hydroxyvitamin D.
There are some other things to consider about the research comparing D2 to D3, the most important of which is that vitamin D2 is probably adequate for most people. Even though D3 might increase vitamin D levels somewhat better than D2, D2 still increases the levels well into and beyond the range that is considered optimal by the Institute of Medicine.
Additionally, much of the research is done on people who already have adequate vitamin D levels. For example, in one of the more recent studies that was included in the meta-analysis mentioned above, a 2011 study by Binkley et al. (54), the average vitamin D levels started out above 72 nmol/l (29 ng/dl) which is well above adequate levels of 50 nmol/l (20 ng/ml) recommended by the Institute of Medicine. It could very well be that at levels this high, the degrading of the vitamin D2 is of no concern (unless someone goes a long time without being able to replenish stores).
All studies in the meta-analysis used vitamin D doses much higher than the DRI of 600 IU per day. At doses closer to the DRI, in people who have low vitamin D levels, it's possible that vitamin D2 and D3 might be virtually indistinguishable in their ability to raise vitamin D back to healthy levels.
Finally, there is some anecdotal evidence. Although I have heard from some vegans who have had a hard time raising their vitamin D levels using D2, many others have succeeded. For example, in June 2010, a vegan who had been diagnosed with vitamin D deficiency wrote me saying that his weekly 50,000 IU of vitamin D2 prescribed by his doctor for 12 weeks succeeded in raising his vitamin D levels from 32.5 nmol/l (13 ng/ml) in January to 180 nmol/l (72 ng/ml) in May. For long-term maintenance, his doctor recommended 1200 IU per day. I heard from another person in December 2010 who raised her levels from 30 to 67 nmol/l (8.1 to 27 ng/ml) with 4,000 IU of vitamin D2 per day for 2 months.
For those vegans whose vitamin D levels do not respond well to vitamin D2, there is a vegan vitamin D3 supplement available from Vitashine, mentioned at the top of this section.
For historical purposes and because some people might want more details, I have left in the research I previously discussed regarding D2 vs. D3 directly below, but I have already hit the important points above and you can click here to skip this research.
Dr. Jacqueline Chan sums up the studies on vitamin D2 vs. D3, "Treatment for most of the studies finding D2 to be less effective than D3 were extremely large boluses given only once, whereas in studies finding them equally effective, the treatment was daily amounts between 400 and 2,000 IU (38)." More recently, a study was published in which large boluses were given repeatedly, on a weekly basis, and D3 increased vitamin D levels more than did D2 (25). Details on this study are provided below, and it does not change my view that vitamin D2 taken consistently should be adequate for most people.
In a 2011 study from Germany, 28,000 IU of vitamin D2 was fed to subjects either in the form of a supplement or from mushrooms, one time per week for four weeks. Vitamin D levels increased from 34 to 57 nmol/l in the mushroom group, and from 29 to 58 nmol/l in the supplement group. The placebo group's vitamin D2 levels decreased over the course of the study (2).
In a 2004 study by Armas et al. (17), subjects were given one dose of 50,000 IU of vitamin D2 or vitamin D3. Vitamin D2 was absorbed just as well as vitamin D3. However, after three days, blood levels of 25(OH)D started dropping rapidly in the subjects who were given vitamin D2, whereas those who received vitamin D3 sustained high levels for two weeks before dropping gradually.
Similarly, a 2011 study by Heaney found that a weekly dose of 55,000 IU of vitamin D3 raised vitamin D levels significantly better than did a weekly dose of 48,000 IU of vitamin D2 (25). The differences in the amounts given were not enough to explain the discrepancy between the increases in vitamin D3. However, some things should be noted. 25(OH)D levels for the D2 group started out at 76.5 nmol/l (30.6 ng/ml), while those in the D3 group started out with levels at 65.0 nmol/l (26.0 ng/ml). In other words, both groups were already replete (according to the Institute of Medicine). The 25(OH)D levels in the D2 group increased to about 130 nmol/l (50 ng/ml) over the course of the study. Finally, two of the authors have financial ties to BTR Group, Inc., a manufacturer of Maximum D3. That is not to say that any data was fudged, just that financial ties can possibly bias one's perspectives.
Trang et al. (19) (1998) found that a daily dose of 4,000 IU of vitamin D3 for two weeks was 1.7 times more effective in raising 25(OH)D levels (which increased 22.5 ± 5 nmol/l (9.0 ± 2 ng/ml)) than 4,000 IU of vitamin D2 (which increased levels 10.5 ± 5 nmol/l (4.2 ± 2 ng/ml)).
Holick et al. (18) (2007) found that a daily dose of 1,000 IU of vitamin D2 over 11 weeks increased 25(OH)D levels from 42 to 67 nmol/l (16.9 to 26.8 ng/ml). Vitamin D3 increased levels similarly, from 49 to 72 nmol/l (19.6 to 28.9 ng/ml). It took 6 weeks for 25(OH)D levels to plateau on that regimen. The study was conducted in Boston and started in February.
Glendenning et al. (39) (2009) compared 1,000 IU of D2 vs. D3 in people with vitamin D insufficiency who had hip fractures. After three months, those who supplemented with D3 had a 31% or 52% (depending on how they were measured) greater increase in 25(OH)D levels than those supplementing with D2. However, parathyroid hormone levels (which can cause bone loss) did not differ between groups, leading the researchers to question whether the difference in 25(OH)D levels were of biological importance.
Gordon et al. (40) (2008), treated 40 infants and toddlers with vitamin D deficiency. Each were assigned to one of three 6-week regimens: 2,000 IU oral vitamin D2 daily, 50,000 IU vitamin D2 weekly, or 2,000 IU vitamin D3 daily. At the end of the trial, participants' 25(OH)D levels went from an average of 42.5 to 90 nmol/l (17 to 36 ng/ml), and there were no significant differences between treatment groups.
Thatcher et al. (41) (2009) gave children with rickets one oral dose of 50,000 IU of vitamin D2 or D3. After three days, 25(OH)D levels rose from approximately 50 to 72 nmol/l (20 to 29 ng/ml) for both groups. Calcitriol (the actual vitamin D hormone) levels also increased similarly in both groups (by about 70%), however, calcium absorption did not increase, leading the researchers to conclude the rickets were not caused by vitamin D deficiency. This should not be a surprise since the baseline average level of 50 nmol/l (20 ng/ml) of 25(OH)D should be adequate to prevent rickets.
Biancuzzo et al. (42) (2010) tested changes in 25(OH)D from a daily dose of 1,000 IU of vitamin D2 or D3 from either orange juice or supplement capsules for 11 weeks at the end of winter. The placebo group received nothing and their 25(OH)D levels decreased slightly. The average 25(OH)D levels of the other four groups (D2 from orange juice, D2 from capsules, D3 from orange juice, D3 from capsules) went up about 25 nmol/l (10 ng/ml) with no significant differences between groups.
Because vitamin D is a fat soluble vitamin, taking vitamin D supplements with foods that contain fat might increase absorption.
A 2010 study explored this (50). A group of people diagnosed with vitamin D deficiency had been prescribed supplements (some D2 and some D3) and were being monitored by the Cleveland Clinic Foundation Bone Clinic. Some of these patients' vitamin D levels had not increased to desired levels. Patients with stubborn vitamin D levels were then instructed to take the vitamin D with meals. After 2 to 3 months of taking with meals, the average vitamin D level went from 30 to 47 ng/ml (75 to 117 nmol/l).
This study had no control group, so it is not clear that the vitamin D levels increased due to taking with meals. It could have been simply because their levels took longer to respond to supplements or because they were exposed to more sunlight during the meal period (the time of year studied was not reported). It should also be noted that even though these subjects' vitamin D levels were more stubborn than other patients, their levels at the beginning of the study were well above those recommended by the Institute of Medicine; the stubborn levels might have been a result of the body regulating vitamin D once it had reached an ideal level rather than an inability to absorb it.
Food manufacturers are now creating large amounts of vitamin D2 in mushrooms by exposing them to commercial ultraviolet light or direct sunlight (55, 56). The vitamin D is well-retained in the mushrooms over the course of the typical storage life of fresh mushrooms, up to two weeks (55, 57). This vitamin D is effective in improving vitamin D status and no different from a vitamin D2 supplement (2).
- The Daily Value for vitamin D is 10 mcg (400 IU). Therefore, if a food label says it has 25% of the daily value, it means it has 2.5 mcg (100 IU) per serving.
- Vitamin D fortified soy, almond, or rice milk normally has 2-3 mcg (80-120 IU) per cup.
2. Urbain P, Singler F, Ihorst G, Biesalski HK, Bertz H. Bioavailability of vitamin D₂ from UV-B-irradiated button mushrooms in healthy adults deficient in serum 25-hydroxyvitamin D: a randomized controlled trial. Eur J Clin Nutr. 2011 Aug;65(8):965-71. doi: 10.1038/ejcn.2011.53. Epub 2011 May 4. | link
7. Bow CH, Cheung E, Cheung CL, Xiao SM, Loong C, Soong C, Tan KC, Luckey MM, Cauley JA, Fujiwara S, Kung AW. Ethnic difference of clinical vertebral fracture risk. Osteoporos Int. 2012 Mar;23(3):879-85. | link
8. Outila TA, Karkkainen MU, Seppanen RH, Lamberg-Allardt CJ. Dietary intake of vitamin D in premenopausal, healthy vegans was insufficient to maintain concentrations of serum 25-hydroxyvitamin D and intact parathyroid hormone within normal ranges during the winter in Finland. J Am Diet Assoc. 2000 Apr;100(4):434-41.
9. Barr SI, Prior JC, Janelle KC, Lentle BC. Spinal bone mineral density in premenopausal vegetarian and nonvegetarian women: cross-sectional and prospective comparisons. J Am Diet Assoc 1998 Jul;98(7):760-5.
13. Parsons TJ, van Dusseldorp M, van der Vliet M, van de Werken K, Schaafsma G, van Staveren WA. Reduced bone mass in Dutch adolescents fed a macrobiotic diet in early life. J Bone Miner Res 1997 Sep;12(9):1486-94.
14. Appleby P, Roddam A, Allen N, Key T. Comparative fracture risk in vegetarians and nonvegetarians in EPIC-Oxford. Eur J Clin Nutr. 2007 Dec;61(12):1400-6. Epub 2007 Feb 7.
15. Bischoff-Ferrari HA, Dawson-Hughes B, Baron JA, Burckhardt P, Li R, Spiegelman D, Specker B, Orav JE, Wong JB, Staehelin HB, O'Reilly E, Kiel DP, and Willett WC. Calcium intake and hip fracture risk in men and women: a meta-analysis of prospective cohort studies and randomized controlled trials. Am J of Clin Nutr. 2007 Dec;86( 6): 1780-1790.
16. Schwalfenberg G. Not enough vitamin D: health consequences for Canadians. Can Fam Physician. 2007 May;53(5):841-54.
17. Armas LA, Hollis BW, Heaney RP. Vitamin D2 is much less effective than vitamin D3 in humans. J Clin Endocrinol Metab. 2004 Nov;89(11):5387-91.
18. Holick MF, Biancuzzo RM, Chen TC, Klein EK, Young A, Bibuld D, Reitz R, Salameh W, Ameri A, Tannenbaum AD. Vitamin D2 is as effective as vitamin D3 in maintaining circulating concentrations of 25-hydroxyvitamin D. 2008 Mar;93(3):677-81. Epub 2007 Dec 18.
19. Trang HM, Cole DE, Rubin LA, Pierratos A, Siu S, Vieth R. Evidence that vitamin D3 increases serum 25-hydroxyvitamin D more efficiently than does vitamin D2. Am J Clin Nutr. 1998 Oct;68(4):854-8. (Abstract)
20. Key TJ, Appleby PN, Spencer EA, Roddam AW, Neale RE, Allen NE. Calcium, diet and fracture risk: a prospective study of 1898 incident fractures among 34 696 British women and men. Public Health Nutr. 2007 Nov;10(11):1314-20.
21. Chan J, Jaceldo-Siegl K, Fraser GE. Serum 25-hydroxyvitamin D status of vegetarians, partial vegetarians, and nonvegetarians: the Adventist Health Study-2. Am J Clin Nutr. 2009 May;89(5):1686S-1692S. Epub 2009 Apr 1.
22. Cashman KD, Wallace JM, Horigan G, Hill TR, Barnes MS, Lucey AJ, Bonham MP, Taylor N, Duffy EM, Seamans K, Muldowney S, Fitzgerald AP, Flynn A, Strain JJ, Kiely M. Estimation of the dietary requirement for vitamin D in free-living adults >=64 y of age. Am J Clin Nutr. 2009 May;89(5):1366-74.
23. Reid IR, Gallagher DJ, Bosworth J. Prophylaxis against vitamin D deficiency in the elderly by regular sunlight exposure. Age Ageing. 1986 Jan;15(1):35-40. (Abstract only.)
24. Toss G, Andersson R, Diffey BL, Fall PA, Larko O, Larsson L. Oral vitamin D and ultraviolet radiation for the prevention of vitamin D deficiency in the elderly. Acta Med Scand. 1982;212(3):157-61. (Abstract only.)
25. Heaney RP, Recker RR, Grote J, Horst RL, Armas LA. Vitamin D(3) is more potent than vitamin D(2) in humans. J Clin Endocrinol Metab. 2011 Mar;96(3):E447-52. Link
26. Smith SM, Gardner KK, Locke J, Zwart SR. Vitamin D supplementation during Antarctic winter. Am J Clin Nutr. 2009 Apr;89(4):1092-8. Epub 2009 Feb 18.
27. Cashman KD, Hill TR, Lucey AJ, Taylor N, Seamans KM, Muldowney S, Fitzgerald AP, Flynn A, Barnes MS, Horigan G, Bonham MP, Duffy EM, Strain JJ, Wallace JM, Kiely M. Estimation of the dietary requirement for vitamin D in healthy adults.Am J Clin Nutr. 2008 Dec;88(6):1535-42.
28. Calvez J, Poupin N, Chesneau C, Lassale C, Tomé D. Protein intake, calcium balance and health consequences. Eur J Clin Nutr. 2012 Mar;66(3):281-95. | link
29. Kerstetter JE, O'Brien KO, Insogna KL. Dietary protein, calcium metabolism, and skeletal homeostasis revisited. Am J Clin Nutr. 2003 Sep;78(3 Suppl):584S-592S. Review.
30. Ho-Pham LT, Nguyen PL, Le TT, Doan TA, Tran NT, Le TA, Nguyen TV. Veganism, bone mineral density, and body composition: a study in Buddhist nuns. Osteoporos Int. 2009 Apr 7. [Epub ahead of print]
31. Bow CH, Cheung E, Cheung CL, Xiao SM, Loong C, Soong C, Tan KC, Luckey MM, Cauley JA, Fujiwara S, Kung AW. Ethnic difference of clinical vertebral fracture risk. Osteoporos Int. 2011 Apr 2. [Epub ahead of print] (Abstract) Link
32. Ho-Pham LT, Nguyen ND, Nguyen TV. Effect of vegetarian diets on bone mineral density: a Bayesian meta-analysis. Am J Clin Nutr. 2009 Jul 1. [Epub ahead of print] PubMed PMID: 19571226.
33. Darling AL, Millward DJ, Torgerson DJ, Hewitt CE, Lanham-New SA. Dietary protein and bone health: a systematic review and meta-analysis. Am J Clin Nutr. 2009 Dec;90(6):1674-92. Epub 2009 Nov 4.
34. Krivosikova Z, Krajcovicova-Kudlackova M, Spustova V, Stefikova K, Valachovicova M, Blazicek P, Nemcova T. The association between high plasma homocysteine levels and lower bone mineral density in Slovak women: the impact of vegetarian diet. Eur J Nutr. 2009 Oct 7.
35. DRI Dietary Reference Intakes Calcium Vitamin D. Committee to Review Dietary Reference Intakes for Vitamin D and Calcium. Food and Nutrition Board. A. Catharine Ross, Christine L. Taylor, Ann L. Yaktine, and Heather B. Del Valle, Editors. Institute Of Medicine of The National Academies. The National Academies Press. Washington, D.C. 2011. Link
36. Crowe FL, Steur M, Allen NE, Appleby PN, Travis RC, Key TJ. Plasma concentrations of 25-hydroxyvitamin D in meat eaters, fish eaters, vegetarians and vegans: results from the EPIC-Oxford study. Public Health Nutr. 2011 Feb;14(2):340-6. Link
37. Michaëlsson K, Melhus H, Warensjö Lemming E, Wolk A, Byberg L. Long term calcium intake and rates of all cause and cardiovascular mortality: community based prospective longitudinal cohort study. BMJ. 2013 Feb 12;346:f228. | link
39. Glendenning P, Chew GT, Seymour HM, Gillett MJ, Goldswain PR, Inderjeeth CA, Vasikaran SD, Taranto M, Musk AA, Fraser WD. Serum 25-hydroxyvitamin D levels in vitamin D-insufficient hip fracture patients after supplementation with ergocalciferol and cholecalciferol. Bone. 2009 Nov;45(5):870-5. Epub 2009 Jul 23. (Abstract)
40. Gordon CM, Williams AL, Feldman HA, May J, Sinclair L, Vasquez A, Cox JE. Treatment of hypovitaminosis D in infants and toddlers. J Clin Endocrinol Metab. 2008 Jul;93(7):2716-21. Epub 2008 Apr 15.
41. Thacher TD, Obadofin MO, O'Brien KO, Abrams SA. The effect of vitamin D2 and vitamin D3 on intestinal calcium absorption in Nigerian children with rickets. J Clin Endocrinol Metab. 2009 Sep;94(9):3314-21. Epub 2009 Jun 30.
42. Biancuzzo RM, Young A, Bibuld D, Cai MH, Winter MR, Klein EK, Ameri A, Reitz R, Salameh W, Chen TC, Holick MF. Fortification of orange juice with vitamin D(2) or vitamin D(3) is as effective as an oral supplement in maintaining vitamin D status in adults. Am J Clin Nutr. 2010 Jun;91(6):1621-6. Epub 2010 Apr 28.
43. Urashima M, Segawa T, Okazaki M, Kurihara M, Wada Y, Ida H. Randomized trial of vitamin D supplementation to prevent seasonal influenza A in schoolchildren. Am J Clin Nutr. 2010 May;91(5):1255-60. Epub 2010 Mar 10. Link
44. Holick MF, Chen TC. Vitamin D deficiency: a worldwide problem with health consequences. Am J Clin Nutr. 2008 Apr;87(4):1080S-6S. Review. Link
45. Manson JE, Mayne ST, Clinton SK. Vitamin D and prevention of cancer--ready for prime time? N Engl J Med. 2011 Apr 14;364(15):1385-7. Link
46. Toner CD, Davis CD, Milner JA. The vitamin D and cancer conundrum: aiming at a moving target. J Am Diet Assoc. 2010 Oct;110(10):1492-500. Link
47. The American Academy of Dermatology. Position Statement on Vitamin D. Amended by the Board of Directors December 22, 2010. Link
48. Fenton TR, Lyon AW, Eliasziw M, Tough SC, Hanley DA. Meta-analysis of the effect of the acid-ash hypothesis of osteoporosis on calcium balance. J Bone Miner Res. 2009 Nov;24(11):1835-40. Link
49. Ho-Pham LT, Vu BQ, Lai TQ, Nguyen ND, Nguyen TV. Vegetarianism, bone loss, fracture and vitamin D: a longitudinal study in Asian vegans and non-vegans. Eur J Clin Nutr. 2011 Aug 3. [Epub ahead of print] Link
50. Mulligan GB, Licata A. Taking vitamin D with the largest meal improves absorption and results in higher serum levels of 25-hydroxyvitamin D. J Bone Miner Res. 2010 Apr;25(4):928-30. Link
51. Ströhle A, Waldmann A, Koschizke J, Leitzmann C, Hahn A. Diet-dependent net endogenous acid load of vegan diets in relation to food groups and bone health-related nutrients: results from the German Vegan Study. Ann Nutr Metab. 2011;59(2-4):117-26. Link
52. Herrmann W, Obeid R, Schorr H, Hübner U, Geisel J, Sand-Hill M, Ali N, Herrmann M. Enhanced bone metabolism in vegetarians--the role of vitamin B12 deficiency. Clin Chem Lab Med. 2009;47(11):1381-7. | link
53. Tripkovic L, Lambert H, Hart K, Smith CP, Bucca G, Penson S, Chope G, Hyppönen E, Berry J, Vieth R, Lanham-New S. Comparison of vitamin D2 and vitamin D3 supplementation in raising serum 25-hydroxyvitamin D status: a systematic review and meta-analysis. Am J Clin Nutr. 2012 Jun;95(6):1357-64. | link
54. Binkley N, Gemar D, Engelke J, Gangnon R, Ramamurthy R, Krueger D, Drezner MK. Evaluation of ergocalciferol or cholecalciferol dosing, 1,600 IU daily or 50,000 IU monthly in older adults. J Clin Endocrinol Metab. 2011 Apr;96(4):981-8. | link
55. Kalaras MD, Beelman RB, Elias RJ. Effects of postharvest pulsed UV light treatment of white button mushrooms (Agaricus bisporus) on vitamin D2 content and quality attributes. J Agric Food Chem. 2012 Jan 11;60(1):220-5. | link
56. Simon RR, Phillips KM, Horst RL, Munro IC. Vitamin D mushrooms: comparison of the composition of button mushrooms (Agaricus bisporus) treated postharvest with UVB light or sunlight. J Agric Food Chem. 2011 Aug 24;59(16):8724-32. | link
57. Roberts JS, Teichert A, McHugh TH. Vitamin D2 formation from post-harvest UV-B treatment of mushrooms (Agaricus bisporus) and retention during storage. J Agric Food Chem. 2008 Jun 25;56(12):4541-4. | link
58. Samelson EJ, Booth SL, Fox CS, Tucker KL, Wang TJ, Hoffmann U, Cupples LA, O'Donnell CJ, Kiel DP. Calcium intake is not associated with increased coronary artery calcification: the Framingham Study. Am J Clin Nutr. 2012 Dec;96(6):1274-80. | link
59. Heaney RP, Weaver CM. Calcium absorption from kale. Am J Clin Nutr. 1990 Apr;51(4):656-7. | link
60. Heaney RP, Weaver CM, Recker RR. Calcium absorbability from spinach. Am J Clin Nutr. 1988 Apr;47(4):707-9. | link
The oxalate content of spinach was calculated measured in this study to be 200 mg of Ca per 477.5 mg of oxalate. 1/2 cup of boiled spinach contains 122 mg of calcium per the USDA database and would, therefore contain
61. Zhao Y, Martin BR, Weaver CM. Calcium bioavailability of calcium carbonate fortified soymilk is equivalent to cow's milk in young women. J Nutr. 2005 Oct;135(10):2379-82. | link
62. Tang AL, Walker KZ, Wilcox G, Strauss BJ, Ashton JF, Stojanovska L. Calcium absorption in Australian osteopenic post-menopausal women: an acute comparative study of fortified soymilk to cows' milk. Asia Pac J Clin Nutr. 2010;19(2):243-9. | link
63. Weaver CM, Heaney RP, Nickel KP, Packard PI. Calcium Bioavailability from High Oxalate Vegetables: Chinese Vegetables, Sweet Potatoes and Rhubarb. Journal of Food Science. 1997 May;62(3):524-5. | link
64. Kenney JJ. Diet and Kidney Stones. Originally posted 4/01/2002. Accessed 3/26/2013. | link
65. Oxalic Acid Content of Selected Vegetables | link. Gives amounts of oxalate in 100 g of the raw, unprepared food (according to correspondence with the USDA Nutrient Data Library 05/13/2013).
66. Weaver CM, Plawecki KL. Dietary calcium: adequacy of a vegetarian diet. Am J Clin Nutr. 1994 May;59(5 Suppl):1238S-1241S. | link
Aloia JF, Patel M, Dimaano R, Li-Ng M, Talwar SA, Mikhail M, Pollack S, Yeh JK. Vitamin D intake to attain a desired serum 25-hydroxyvitamin D concentration. Am J Clin Nutr. 2008 Jun;87(6):1952-8.
Dawson-Hughes B. Racial/ethnic considerations in making recommendations for vitamin D for adult and elderly men and women. Am J Clin Nutr. 2004 Dec;80(6 Suppl):1763S-6S.
Fairweather-Tait SJ, Johnson A, Eagles J, Ganatra S, Kennedy H, Gurr MI. Studies on calcium absorption from milk using a double-label stable isotope technique. Br J Nutr. 1989 Sep;62(2):379-88. | link
Freedman BI, Wagenknecht LE, Hairston KG, Bowden DW, Carr JJ, Hightower RC, Gordon EJ, Xu J, Langefeld CD, Divers J. Vitamin d, adiposity, and calcified atherosclerotic plaque in african-americans. J Clin Endocrinol Metab. 2010 Mar;95(3):1076-83. Epub 2010 Jan 8. (Abstract)
Heaney RP, Davies KM, Chen TC, Holick MF, Barger-Lux MJ. Human serum 25-hydroxycholecalciferol response to extended oral dosing with cholecalciferol. Am J Clin Nutr. 2003 Jan;77(1):204-10.
Houghton LA, Vieth R. The case against ergocalciferol (vitamin D2) as a vitamin supplement. Am J Clin Nutr. 2006 Oct;84(4):694-7.
This paper argued that vitamin D2 should not be used for fortification or supplementation. The authors state:
"Vitamin D2, if given in high enough doses, prevents infantile rickets and is capable of healing adult osteomalacia. However, the inefficiency of vitamin D2 compared with vitamin D3, on a per mole basis, at increasing 25(OH)D is now well documented, and no successful clinical trials to date have shown that vitamin D2 prevents fractures (19 - 21, 47)."
But references 19-21 were not studies looking at whether D2 prevents fractures. They include references 19 (Trang et al.) and 17 (Aramas, et al.) cited above, as well as this study:
Mastaglia SR, Mautalen CA, Parisi MS, Oliveri B. Vitamin D2 dose required to rapidly increase 25OHD levels in osteoporotic women. Eur J Clin Nutr. 2006 May;60(5):681-7.
Their final citation was a book on vitamin D from 1985, and though I'm not certain, I'm skeptical that it includes any studies comparing D2 and D3's affects on bone fractures:
Norman AW, Schaefer K, Grigoleit H-G, Vaamonde J, eds. Vitamin D, chemical, biochemical and clinical update. Berlin, Germany: Walter deGruyter, 1985;3-12
Romagnoli E, Mascia ML, Cipriani C, Fassino V, Mazzei F, D'Erasmo E, Carnevale V, Scillitani A, Minisola S. Short and long-term variations in serum calciotropic hormones after a single very large dose of ergocalciferol (vitamin D2) or cholecalciferol (vitamin D3) in the elderly. J Clin Endocrinol Metab. 2008 Aug;93(8):3015-20. Epub 2008 May 20.