Vitamin D and tuberculosis: hope or hype?
It may be worthwhile to test for and treat vitamin D deficiency in latent infection, but not in active TB
In this issue of the Journal, MacLachlan and Cowie advocate increased testing of vitamin D (serum 25-hydroxyvitamin D [25-OHD]) for people with risk factors for vitamin D deficiency and tuberculosis (TB).1 This pertinent suggestion is based on the assumption that vitamin D deficiency is a risk factor for progression from latent to active TB, and that correction of deficiency could reduce this risk (the demonstration by MacLachlan and colleagues2 of TB seasonality in Australia is consistent with this hypothesis). The proposal presents a timely opportunity to scrutinise evidence of an association between vitamin D deficiency and TB, temper the high hopes that vitamin D might be an important adjunctive treatment for active TB, and remind clinicians about problems with testing and interpreting 25-OHD levels.
Many communicable diseases are seasonal — for example, influenza, rotavirus and TB. But many potential risk factors are also seasonal — temperature, time spent indoors, household crowding, humidity, ultraviolet radiation (which has immunological effects independent of vitamin D),