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Health Effects of Vitamin D: The "D"-bate Goes On

Does vitamin D deficiency itself underlie the association with cognitive decline (and other conditions), or does it reflect an unhealthy lifestyle?

Several health effects have been attributed to vitamin D, including lower rates of fractures, reduced rates of certain types of cancer, and diminished risk for diabetes and heart disease. Investigators used data from the InCHIANTI database collected in Italy from 1998 to 2006 to examine a possible relation between vitamin D levels and decline in mental function among the elderly.

A total of 858 subjects aged 65 and older underwent cognitive testing at baseline and after a median follow-up period of 6 years. At baseline, cognitive performance scores were significantly lower in participants deficient in vitamin D than in those with sufficient levels. Participants with severe deficiency (<25 nmol/L serum 25-hydroxyvitamin D) were more likely than those with sufficient levels (75 nmol/L) to experience declines in mental function over the observation period. The authors conclude that vitamin D supplementation may prevent mental decline in the vitamin-D–deficient elderly.

Commentators suggest that the broad range of conditions associated with vitamin D deficiency may not necessarily be caused by low vitamin D but may instead reflect a less healthy lifestyle. If so, vitamin D supplementation might not reduce cognitive decline or lower risks for cancer, diabetes, or heart disease. The commentators cite controlled clinical trials that demonstrated no benefit of vitamin D supplementation on overall risk for fractures, obesity, or type 2 diabetes.

Comment: Why is this important to dermatologists? Recommendations concerning exposure to sunlight are based on conclusions from similar epidemiologic studies. At present, the evidence is insufficient to conclude that sun exposure will — or will not — prevent diseases attributed to vitamin D deficiency. Without such evidence, it is impossible to assess the risk:benefit ratio of increased sun exposure. (However, it is quite clear that tanning bed exposure carries much greater risks than any benefit these devices might provide.) I agree with the editorialists' suggestion that randomized clinical trials be performed to carefully assess the health benefits of supplementation in vitamin-D–deficient patients.

— Craig A. Elmets, MD

Published in Journal Watch Dermatology July 23, 2010

Citation(s):

Llewellyn DJ et al. Vitamin D and risk of cognitive decline in elderly persons. Arch Intern Med 2010 Jul 12; 170:1135.

• Original article (Subscription may be required)
• Medline abstract (Free)

Grey A et al. A place in the sun? Arch Intern Med 2010 Jul 12; 170:1099.

• Original article (Subscription may be required)
• Medline abstract (Free)

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