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Vitamin D and stroke

COPENHAGEN, DENMARK. Vitamin D deficiency as measured by 25-hydroxyvitamin D (25(OH)D) levels is associated with risk factors for stroke such as hypertension, thrombosis, atherosclerosis and inflammation. Consistent with this, observational studies have suggested that the risk of ischemic (clot induced) stroke increases with reduced vitamin D status, although the results have been inconsistent.

A new study has just reported what appears to clarify this matter significantly. Approximately 10,000 residents of Copenhagen for whom baseline 25(OH)D has been obtained were followed for 21 years, during which 1256 ischemic strokes were observed. A stepwise increase in ischemic stroke was found associated with a stepwise decrease in 25(OH)D levels. A comparison of those deficient (< 6 mg/dL) with those considered sufficient (equal to or greater than 30 mg/dL) yielded an increase in relative risk of 36% (absolute risk increase of 2%). If the comparison was with percentile categories, then individuals in the lowest category (severely deficient) had an 82% relative risk increase (absolute risk increase of 5%) compared to subjects in the highest groups (50% to 100% group). These risk increases were obtained after adjusting for confounding. Cumulative incidence increased exponentially with age with the incidence associated with vitamin deficiency always higher than that for sufficiency.

The authors also performed a meta-analysis (weighted pooled analysis of 10 studies including theirs). Increases in risk of a stroke due to deficiency ranged from 46% to 56% depending on the model used. These results were statistically significant with fairly tight confidence limits. Thus the association appears confirmed and adds to the importance of maintaining adequate vitamin D levels.

Supplementation with vitamin D was unusual in the study population. If one accepts that 50 ng/dL is optimum, then all subjects fell considerably below this level. One can only speculate regarding the results if the study had included subjects with ideal levels. But the prevalence of stroke is rather low, and if studies were now undertaken to clarify these issues, a very large intervention cohort would be required to obtain significant results. Vitamin D is not a money making prescription drug and thus we may never know the answer.

Brondum-Jacobsen P, Nordestgaard BG, Schnohr P, Benn M. 25-hydroxyvitamin D and symptomatic ischemic stroke: an original study and meta-analysis. Ann Neurol 2013 January;73(1):38-47

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