DHA Recommendations Follow-Up
After I published my last post, DHA Recommendations Updated (A Bit), I received comments from a reader saying that there is no evidence that vegans need to supplement with DHA. So, I went digging for the evidence.
The first bit comes from the experience of Joel Fuhrman, MD, which I blogged about in November of 2010 in the post DHA Supplements: A Good Idea, Especially for Older Vegan Men, in which Dr. Fuhrman said that he has been seeing numerous elderly vegans with severe DHA deficiency, and he believes it may have exacerbated Parkinson’s disease and tremors in some of his patients.
Is there any evidence for a connection here? I’m not an expert on the literature regarding DHA and the brain, but here is an excerpt from a 2005 study that indicates it’s plausible:
“Docosahexaenoic acid (DHA), a dietary essential omega-3 fatty acid concentrated in membrane phospholipids at synapses and in retinal photoreceptors is decreased in [the Alzheimer disease] brain. This deficiency may be due to enhanced free radical–mediated lipid peroxidation, decreased dietary intake, and/or impaired liver DHA shuttling to the brain. Decreased DHA serum content correlates with cognitive impairment. Moreover, epidemiologic studies suggest neuroprotective consequences of diets enriched in omega-3 fatty acids (1).”
Note the part, “impaired liver DHA shuttling to the brain.” I would assume, then, that an important way that DHA gets to the brain is by being produced by the liver (or eaten) and shuttled via the blood. So if vegans have low blood levels of DHA (as they do, without supplementation), that could mean they are not getting enough to the brain.
The second bit is less strong, but comes from the paper, Mortality in British Vegetarians, a 2002 report showing that vegetarians in the Oxford Vegetarian Study had twice the risk of dying from a mental or neurological disease as did non-vegetarians (see Disease Rates of Vegetarians and Vegans). A different report, from the Adventist Health Study, found the opposite: vegans and lacto-ovo vegetarians had half the risk of dementia (2).
I tend to think the culprit in these disparate findings is vitamin B12 (not DHA), as Seventh-day Adventists have traditionally known to supplement with vitamin B12 whereas other populations of vegans have neglected it. But I would not completely rule out DHA at this time.
My sense is that kids who are raised vegan are rarely supplemented with DHA and to our knowledge most of them develop normally. This would indicate that dietary DHA is not necessary for optimal health. But none of these children have made it to old age (that I am aware of) to know if the situation changes as they get older. It could be that people born without a source of DHA past infancy become highly efficient at converting ALA to DHA, an ability that might not be developed in people who become vegetarian as adults.
While I would love nothing more than to dispense with the entire DHA/omega-3 issue, I just don’t believe we can do that unless future research proves there is nothing to be concerned about.
1. Lukiw WJ, Cui JG, Marcheselli VL, Bodker M, Botkjaer A, Gotlinger K, Serhan CN, Bazan NG. A role for docosahexaenoic acid-derived neuroprotectin D1 in neural cell survival and Alzheimer disease. J Clin Invest. 2005 Oct;115(10):2774-83. | link
2. Giem P, Beeson WL, Fraser GE. The incidence of dementia and intake of animal products: preliminary findings from the Adventist Health Study. Neuroepidemiology. 1993;12(1):28-36. | link