Out of the shadows: A sunny outlook on TB
Link asserted between vitamin D, recrudescence
Does vitamin D deprivation hasten the development of TB disease? If you’re ready for a long and thoughtful answer to that question, you might want to call up William W. Stead, MD, longtime TB clinician and the now-retired director of TB control in Arkansas.
Stead says he was attending a conference in Washington, DC, last December, when the import of one of the presentations struck him like a bolt of lightning. A presenter was talking about foreign-born health care providers, all skin-test positive, who had opted to skip preventive therapy and subsequently were diagnosed with active TB. The diagnoses didn’t come just any time of year, mind you, but in the summer, after — Stead hypothesizes — a winter’s worth of sunlight deprivation may have precipitated their illness.
"I was quivering with excitement," says Stead. "After the presentation I jumped to my feet and said, I hope you’ll forgive an 81-year-old man who’s as excited as hell!’" The audience appeared glad to indulge him.
For years, Stead explained, he’s followed the connections between vitamin D, its apparent effects on the immune system, and TB.
It started with researcher A. Stewart Douglas, who explored the connection between time of year, sunlight deprivation, and the recrudescence of TB among immigrants to England from the Indian subcontinent. "These people come from a tropical area where there’s lots of sun, and where people wear light clothing," Stead explains. "Then they go to Liverpool or Birmingham, where it’s cold and wet, and they suffer sunlight deprivation." Douglas found a strong link between chronology and time of diagnosis: That is, after enduring a dark and chilly English winter, they’d turn up with disease the following summer.
Caucasians don’t think much about the vitamin D connection, because they are protected against the vitamin shortage by drinking fortified milk. "But 80% to 90% of dark-skinned people are, to some extent, lactose intolerant; they generally eschew milk," Stead adds.
Stead turned up more research that bolstered the argument. In vitro studies showed a considerable effect of vitamin D on macrophages and T cells; what’s more, Stead’s longtime friend and colleague, TB expert Alfred J. Crowle, found another curious link: macrophages of healthy African-Americans, even when not vitamin D-deprived and otherwise healthy, appeared to be more "permissive" in the laboratory of the multiplication of TB than macrophages of healthy whites. If the same holds true in vivo, that would leave dark-skinned, lactose-intolerant people even more vulnerable to sunlight deprivation, the reasoning goes.
Still not convinced? Stead directs listeners to a recent account (in the New England Journal of Medicine) of a boy from Marshall Islands found (in summer) to have cavitary disease — a rarity in one so young, but again, Stead suggests, perhaps linked to the striking difference in latitudes between the sunlit Marshall Islands and the chilly reaches of North Dakota.
An account in Annals of Internal Medicine may hold a similar moral: An unusual number of cases of TB occurred in a jail over a two-year period; inmates there, most of them African-American, had spent long months indoors, where their chief recreation was lots of basketball played in — guessed it already? — an indoor court, artificially lit.
References
1. Rook G. The role of vitamin D in tuberculosis. Am J Respiratory Dis 1988; 138:766-70.
2. Provvodini, Manalagos. 125-Dihydroxy Vitamin D: A novel immunoregulatory hormone. Science 1984; 124:1,338-1,341.
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