In several of the less-well-punctuated corners of the internet (and on Fox News), I have found discussions of vegetarianism which posed the question, ‘Does being a vegetarian or vegan make your brain shrink?’ These discussions usually answered in the affirmative, and referenced an Oxford study. My interest was piqued by this for two reasons. First, I have read the much-publicized study BMJ study that found that high IQ children were more likely to become vegetarians as adults. Second, I am not a vegetarian or vegan, and it is always nice to feel that one’s preferences have scientific backing.
So, I went and found that Oxford study, which was published in Neurology in 2008, and which is un-excitingly titled, “Vitamin B12 status and rate of brain volume loss in community-dwelling elderly”.
Vitamin B12, also called cobalamin, is an essential vitamin. Plants and animals are unable to synthesize B12 themselves, which means that they must consume it. Herbivores accomplish this in two main ways, either by carrying around B12-producing bacteria in their rumen, or by fermenting plant material in their hindgut and then re-ingesting it (cecotropism).
Non-herbivorous animals get their B12 by eating herbivorous animals, or by eating their milk or eggs. This presents a problem for vegetarians, and an even bigger one for vegans. It’s been known for some time that a vitamin B12 deficiency during gestation can result in developmental delays of more or less severity in infants, and these deficiencies have been observed in vegetarian and vegan mothers (although I was unable to find evidence that it was wildly common). Vitamin B12 deficiency has deleterious effects on adult health as well, and can result in permanent nervous system and brain damage within six months.
However, nowadays worried vegetarians and vegans can take vitamin supplements to make sure that their B12 levels are within the normal range. The Oxford study (Vogiatzoglou, et al.) is intriguing because it looks at differences in aging in a population of elderly people all of whom had vitamin B12 levels within the normal range. The study examines differences in outcome based on relative “healthy” levels of B12, and they found that individuals with B12 levels in the bottom third of the healthy range had three times the risk of diminished brain volume than individuals in the top third. Put another way, low but normal B12 levels increase the risk of significant brain atrophy.
One proposed mechanism of action is that vitamin B12 deficiency causes white matter demyelination, or death of the myelin sheath on neurons. Myelin is a material that coats the projections of brain cells and nerves, and allows signals to move along them. That is how the cells of the nervous system communicate with one another, and without myelin they cannot do it. Without communicative input and ability, neurons die.
It is certainly conceivable that vegans and vegetarians, who do not get B12 in their diet and so must seek out supplements, might have lower average B12 levels and so an increased risk of brain atrophy in their old age. However, that is not that this study shows. The authors did not examine vegetarian diets, and so could not have demonstrated a link between vegetarian diet and low B12 levels. Even more, an increased risk of brain atrophy at the end of life is not the same as on-going cognitive impairment. So, if being a vegan makes you stupid, this study didn’t prove it.