Research on Vegetarians & Vegans

Below is a summary of the research done on mortality and disease rates of vegetarians. There are also links to more detailed articles.

For a concise explanation of the different types of studies and their pros and cons, please see the article, Nutrition Research: What You Should Know.

There have been six large epidemiological studies looking at Western vegetarians. The first five were the Oxford Vegetarian Study, the Adventist Mortality Study, the Health Food Shoppers Study, the Adventist Health Study, and the Heidelberg Study. The abstract of a compilation of the data from these five studies can be found here, and is also discussed below under "1999 Meta-analysis."

The sixth study of British vegetarians and vegans, the Oxford component of the European Prospective Investigation into Cancer and Nutrition (EPIC-Oxford) is currently in progress. Preliminary results are discussed below under "2003 Epic-Oxford Preliminary Results."

A seventh prospective study, Adventist Health Study-2 (AHS-2), is now under way. As of 5/31/2007 there were 96,000 subjects recruited. Data analyzed to date suggest that 4.2% of subjects are vegans and 31.6% lacto-ovo vegetarians, making it the largest prospective study of Western vegetarians.

Adventist Health Study¹

The Adventist Health Study is the only major study on the general health and mortality of vegetarians in the U.S. Many members of the Seventh-day Adventist Church are vegetarian. Here are some details:

Data collected from 1976-1988
34,192 participants, members of the Seventh-day Adventist church
29% were vegetarian
7-10% of the vegetarians were vegan.

Results were:

	Men		Women
	Vegetarians	Non-vegetarians	Vegetarians	Non-vegetarians
BMI	24.3	26.2	23.7	25.9
Heart disease	38% Lower for Men		No Difference for Women
Overall mortality	Lived 3.21 more yrs		Lived 2.52 more yrs
BMI - Body Mass Index. A measure of healthy body weight. Lower than 20 is underweight, while ≥ 25 is overweight.

Compared to the non-vegetarians, vegetarians had about:

1/2 the high blood pressure and diabetes
1/2 the colon cancer
2/3 the rheumatoid arthritis and prostate cancer
Breast, lung, and uterine cancers tended to be lower in vegetarians but could have been due to random chance.

Life expectancies in the Adventist Health Study were published in 2001.² They showed that white, non-Hispanic Seventh-day Adventists live longer than other white Californians (7.28 years for men, 4.42 years for women). According to the researchers, this group of Seventh-day Adventists were the longest-lived, formally studied population in the world (with an average life span of 78.5 years for men, 82.3 for women).

The following variables were shown to increase life expectancy:

vegetarian diet
eating nuts regularly
physical activity
lower body weight
no smoking

The only other variable looked at was hormone replacement therapy for women which possibly contributed to increased life expectancy.

Vegetarian Mortality Rates

1999 Meta-analysis

In 1999, data were published from the 4 largest studies (the Adventist Health Study, the Adventist Mortality Study, the Oxford Study, and the Heidelberg Study) analyzing vegan mortality rates (the Health Food Shoppers Study was left out because it was not clear who was vegan and who was lacto-ovo vegetarian).³ The data compared the risk of dying from various diseases between people with different diets but who had similar lifestyles. The standardized mortality ratios (SMR) in 3 of the studies showed less mortality in these groups than in the population at large (no SMR was calculated for the 4th study). Most of this difference was thought to be due to lower smoking rates in the study groups, but some difference may have been due to a generally healthier diet overall than in the population at large.

Compared to 31,766 people who ate meat at least once per week:

Occasional meat eaters (8,135 people who ate meat less than once per week) had a 20% reduced rate of dying of heart disease and a 10% reduced rate of overall mortality.
Those who ate no meat other than fish (2,375 people) had a 34% reduced rate of dying from heart disease and an 18% reduced rate of overall mortality.
Lacto-ovo vegetarians (23,265 people) had a 38% reduced rate of dying from lung cancer, a 34% reduced rate of dying from heart disease, and a 15% reduced rate of mortality.
Vegans (753 people) had a 26% reduced rate of dying from heart disease (however the difference was not statistically significant, meaning that it could have been due to random chance) and their mortality was the same as the regular meat-eaters.

2003 Epic-Oxford Preliminary Results

In 2003, preliminary results from EPIC-Oxford comparing death rates of 46,562 subjects were reported. About 33% of the subjects were vegetarian (including many vegans). The results showed no statistically significant differences between the vegetarians and non-vegetarians in any of the mortality categories which included cancer, circulatory disease, ischemic heart disease, cerebrovascular disease (stroke), all other causes, and all causes combined.