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Health

Vitamin D responsible for racial disparities in health?

Gene ExpressionBy Razib KhanJanuary 7, 2010 2:23 PM

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I got interested in vitamin D a few years ago because I was trying to figure out a plausible explanation for why many of the genetic variants implicated in lighter skin seem to have risen in frequency relatively recently, 10,000 years ago, when modern humans have been extant at higher latitudes on the order of 30,000 years. So I started mooting the speculative idea that the switch to agriculture might have reduced vitamin D levels. Initially I assumed that rickets was the main issue, but over the past few years there has been a veritable explosion in the medical literature pointing to correlations between ill health and low vitamin D levels. The proportion of these which are randomized controlled trials are low. Unfortunately, health related topics tend to go through fads, so I've not been posting much about vitamin D. But this report is interesting, Study Links Vitamin D, Race and Cardiac Deaths:

Lead author Kevin Fiscella, M.D., said a complex host of genetic and lifestyle factors among blacks may explain why this population group has lower vitamin D levels across the lifespan than other races. People get vitamin D through their diets, sun exposure, and oral supplements. Genetic factors common to blacks sometimes preclude vitamin D absorption, such as a higher incidence of lactose intolerance, which can eliminate vitamin-D fortified milk from the diet, and darker skin pigment that significantly reduces vitamin D synthesis. ... Overall, the analysis showed that, as expected, a vitamin D deficiency was associated with higher rates of death among all people in the sample. In fact, those adults with the worst deficiency had a 40 percent higher risk of death from cardiac illness. This suggests that vitamin D may be a modifiable, independent risk factor for heart disease, Fiscella said. Most striking, however, was that when researchers adjusted the statistics to look at race, blacks had a 38 percent higher risk of death than whites. As vitamin D levels rose, however, the risk of death was reduced. The same was true when researchers analyzed the effect of poverty on cardiovascular death rates among blacks, which suggests that vitamin D deficiency and poverty each exert separate risk factors, the study said.

The abolition of poverty is going to be a herculean task, but vitamin D supplementation is doable. But even the lead author expresses caution about these sorts of supplementation silver bullets:

Fiscella cautions, however, that not all observational studies of vitamin deficiency are borne out by subsequent clinical trials. For example, previous observational studies of vitamin E and beta-carotene that were associated with poor heart health did not hold up in later clinical studies. The need to further assess the vitamin D connection to heart disease is convincing, however, particularly among blacks, he added.

Slate just published a piece on vitamin crazes. It concludes:

That's not to say that vitamins aren't important. Vitamins are critical to all sorts of bodily functions, and we have to get them through diet because our bodies can't make them on their own. The Office of Dietary Supplements at the NIH recommends that we get certain levels of a variety of kinds of vitamins, and that recommendation is sound. But encouraging us to get a complete suite of vitamins is not the same as suggesting that we get them by popping a pill. In fact, the reports littering the ODS site seem to converge upon the same point: There is some good news for supplements, but it's extremely limited. The 2006 NIH panel, for instance, concluded that postmenopausal women should probably take calcium and vitamin D to safeguard their bones; that pregnant women should keep taking folate; and that adults with age-related macular degeneration, an eye disease, should take a combination of antioxidants and zinc. But beyond that, the panel's strongest recommendation was that scientists conduct further research on the risks and benefits of vitamins. For every study that turns up disconcerting vitamin side effects, there seem to be two more that conclude that we simply don't know enough yet about supplements to make evidence-based recommendations.

No one doubts the relationship between vitamin D deficiency and rickets at least.

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