New study suggests vitamin D deficiency linked to increased stroke risk

New study suggests vitamin D deficiency linked to increased stroke risk
February 3, 2012 -- Dr John Cannell

On February 2nd, researchers at the University of Alabama announced that sunlight is inversely associated with stroke: the more sunlight the fewer strokes. The authors also commented on the poor wisdom of avoiding all sunlight; that is, they implied the dermatologists have done us harm.

Lack of Sunlight May Raise Stroke Risk

Strokes are the third leading cause of death in the USA, but the leading cause of disability. High blood pressure is the single most important modifiable medical risk factor, but inflammation (as measured by CRP) and diabetes are major medical risk factors as well. Blacks are twice as likely as Whites to suffer a stroke, even after scientists account for all the socioeconomic and medical risk factors. Why do so many more Blacks die from strokes as Whites?

It is not vitamin D, according to Dr. Erin Michos and colleagues in a paper just published in the journal Nutrition. However, the researchers found that vitamin D levels were a major risk factor for Whites but not for Blacks. Whites with low vitamin D levels (<15 ng/ml) had a threefold higher risk for stroke compared to Whites with higher levels. This is one of those studies where they collected blood in the late 1980s and early 1990s, froze it, and then waited to see who died of what and when over the next 14 years.

Michos ED, et al. 25-Hydroxyvitamin D deficiency is associated with fatal stroke among whites but not blacks: The NHANES-III linked mortality files. Nutrition. 2012 Jan 18. [Epub ahead of print]

For Whites, all the traditional risk factors were strongly influenced by 25(OH)D levels (p= <0.0001) including, you guessed it, CRP. For Whites in the highest quartile of vitamin D levels (mean = 44 ng/ml), they had much lower CRP (.35 vs. .48), less diabetes (4.1 % vs. 8.9%), less hypertension (22% vs. 35%) and less cholesterol problems (22% vs. 31%) than the Whites in the lowest quartile of vitamin D (mean=17 ng/ml). They could not find similar robust finding for Blacks, and they hypothesized that perhaps Blacks can get along with less vitamin D than Whites can. That certainly does not appear to be the case in equatorial Africa.

I suspect they couldn’t find the relationship here because American Blacks have such low vitamin D levels, that the range in blood levels is not large enough to show clinical or statistical significance. That is, so many American Blacks are deficient and at risk of stroke, the number with vitamin D levels high enough to help prevent stroke are negligible. As I said, the authors note another possibility, that vitamin D metabolism is different in Blacks. Although possible, I think it’s best to treat the massive deficiency in the Black community first. I suspect researchers will find that deficiency is deficiency, no matter the skin color.