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In the present issue of the Canadian Respiratory Journal, Gilbert et al (1) ( pages 75–80), review the potential roles of vitamin D in lung disease. They point out the considerable current interest in the subject, related to multiple, potentially useful actions of the vitamin in bench-type experiments. Apparently, vitamin D has anti-inflammatory and immunomodulating properties, and blood levels are often decreased in patients with chronic lung disease. In The National Health and Nutrition Examination Survey of healthy Americans (2), spirometric values were inversely related to vitamin D levels, after correction for potential confounders. Vitamin D binding proteins have been implicated in the development of chronic obstructive pulmonary disease (COPD), with certain genetically determined variances in these proteins both increasing and decreasing COPD risk (1). Asthma has been believed either more or less likely to develop in people with low vitamin D levels; this appears to be a very active field of investigation.
Indeed, the May 1, 2009, issue of the American Journal of Respiratory and Critical Care Medicine contained two articles with accompanying editorials regarding vitamin D and lung diseases, one concerning asthma (3,4), the other concerning tuberculosis (TB) (5,6). The asthma paper (3) was an epidemiological study showing that low vitamin D levels were associated with asthma in Costa Rican children, while the TB article (5) reported a negative trial of supplemental vitamin D in West Africa. The editorials (4,6) were both confusing and enlightening. They pointed out that the merits of vitamin D were controversial, with evidence that it may actually promote both asthma and allergies, and while severe vitamin D deficiency might promote TB, less severe deficiency may not. Furthermore, they pointed out that ‘normal’ vitamin D levels are controversial, and that levels usually found in disease are higher than those associated with frank bone disease – the classic outcome of vitamin D deficiency. Therefore, if supplemental vitamin D trials are to be performed, the dose and the desirable serum levels that result are also difficult questions. We are left with the certainty that vitamin D can influence immune responses, whether this is for good or ill is unclear. It is also unclear whether this influence is readily achievable with the usual levels of vitamin supplementation.
The vitamin D issue seems particularly relevant in Winnipeg, Manitoba, this year. We have had a long, cold and dark winter, followed by a dark, wet spring that was not particularly warm. These are just the kind of conditions that deplete one’s vitamin D; clothing and lack of sunlight have been postulated as causes of the asthma epidemic (ST Weiss, personal communication). I am feeling vulnerable, and my mood was not improved by an article that appeared in the the Winnipeg Free Press (7) reporting that vitamin D was good for the aging brain. Perhaps I should go and buy some.