Vegan For Life
by Jack Norris, RD &
Ginny Messina, MPH, RD
Mild B12 Deficiency - Dementia & Depression
Last updated October, 2011
Summary: There is evidence that long-term, mild B12 deficiency can lead to impaired cognitive function, dementia, and depression.
Two literature reviews from 2000 (1, 2) note that people with Alzheimer's disease have elevated homocysteine (a marker of low folate, B12, or vitamin B6 status), elevated methylmalonic acid (MMA, a metabolite indicating low B12 status), low blood B12 levels, or low blood folate levels; although the data is somewhat mixed (3). A 2009 meta-analysis of prospective studies (4) showed elevated homocysteine to be associated with risk of Alzheimer's disease. In some cases, B12-deficient dementia (which is a concern in itself) may be misdiagnosed as Alzheimer's disease (5).
A 2008 meta-analysis of vitamin supplementation and cognitive function found little benefit for people already diagnosed with dementia, but did improve cognition in elderly people with elevated homocysteine but who were not diagnosed with dementia (6). Another 2008 study found that vitamin supplementation did not slow cognitive decline in people with mild to moderate Alzheimer's disease (7).
While the data is still preliminary, it appears that homocysteine and dementia might follow a similar pattern to cardiovascular disease: lowering homocysteine can prevent problems for people who have not yet developed dementia, but once someone has dementia it might be too late for vitamin supplementation to help.
A 2011 study from Chicago Health and Aging Project (9), found that poor vitamin B12 status in older age is frequently missed by measuring serum vitamin B12 levels alone. Their findings suggested that MMA, the specific marker of B12 deficiency, may affect cognition by reducing total brain volume, whereas the effect of elevated homocysteine on cognition may be caused by increasing white matter hyperintensity volume (WMHV) and strokes.
A 2002 report from the Oxford Vegetarian Study (8) showed that while overall mortality was the same between vegetarians and non-vegetarians, vegetarians had 2.2 times the death rate from mental and neurological diseases (the finding barely reached statistical significance). A low vitamin B12 intake seems like a likely explanation for this finding.
There is evidence that depression is often related to B12 deficiency. Some evidence suggests B12 deficiency can be confined to the brain. In such cases, massive doses of methylcobalamin might be necessary to replete B12 stores in the brain.
Syd Baumel, a vegan activist and science writer from Winnipeg, Canada, has written an article on this topic, A Shot in Time Saves Mind: Vitamin B12 and Depression.
1. Nourhashemi F, Gillette-Guyonnet S, Andrieu S, Ghisolfi A, Ousset PJ, Grandjean H, Grand A, Pous J, Vellas B, Albarede JL Alzheimer disease: protective factors. Am J Clin Nutr. 2000 Feb;71(2):643S-649S.
4. Van Dam F, Van Gool WA. Hyperhomocysteinemia and Alzheimer's disease: A systematic review. Arch Gerontol Geriatr. 2009 May-Jun;48(3):425-30. Epub 2008 May 13. Review. (Abstract)
6. Malouf R, Grimley Evans J. Folic acid with or without vitamin B12 for the prevention and treatment of healthy elderly and demented people. Cochrane Database Syst Rev. 2008 Oct 8;(4):CD004514.
7. Aisen PS, Schneider LS, Sano M, Diaz-Arrastia R, van Dyck CH, Weiner MF, Bottiglieri T, Jin S, Stokes KT, Thomas RG, Thal LJ; Alzheimer Disease Cooperative Study. High-dose B vitamin supplementation and cognitive decline in Alzheimer disease: a randomized controlled . JAMA. 2008 Oct 15;300(15):1774-83.
8. Appleby PN, Key TJ, Thorogood M, Burr ML, Mann J. Mortality in British vegetarians. Public Health Nutr. 2002 Feb;5(1):29-36. Abstract
9. Tangney CC, Aggarwal NT, Li H, Wilson RS, Decarli C, Evans DA, Morris MC. Vitamin B12, cognition, and brain MRI measures: A cross-sectional examination. Neurology. 2011 Sep 27;77(13):1276-82. Link