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Vitamin D and Tuberculosis Incidence in Spain

In commenting on our article (1), Dr. Pérez-Trallero and colleagues present data from two ecological studies describing an association between decreased exposure to sunlight and susceptibility to tuberculosis in Spain. While such studies are potentially subject to confounding, their interesting findings are consistent with the hypothesis that vitamin D deficiency contributes toward susceptibility to tuberculosis in this setting. We note that mean 25 hydroxyvitamin D [25(OH)D] concentration associated with increased incidence of tuberculosis among Basque valley-dwellers (18.6 ng/ml, or 46.5 nmol/L) was significantly higher than among TB contacts in London, United Kingdom (12.0 ng/ml, or 30.0 nmol/L). If this association is causal, then it may be that the threshold 25(OH)D concentration required for optimum protection against tuberculosis is higher than the 20-nmol/L cutoff which defines profound deficiency (2). Vitamin D "insufficiency" [serum 25(OH)D < 75 nmol/L] (3) is widely reported in the Middle East and India, where it is associated with poor nutrition, veiling, and urbanization (4). The importance of low vitamin D status as a risk factor for tuberculosis in sunny countries may be underestimated.

Adrian R. Martineau

Queen Mary's School of Medicine and Dentistry
Barts and The London
London, United Kingdom

Robert J. Wilkinson

University of Cape Town
Cape Town, South Africa

Christopher J. Griffiths

Queen Mary's School of Medicine and Dentistry
Barts and The London
London, United Kingdom

FOOTNOTES

Conflict of Interest Statement: None of the authors has a financial relationship with a commercial entity that has an interest in the subject of this manuscript.

REFERENCES

1. Martineau AR, Wilkinson RJ, Wilkinson KA, Newton SM, Kampmann B, Hall BM, Packe GE, Davidson RN, Eldridge SM, Maunsell ZJ, et al. A single dose of vitamin D enhances immunity to mycobacteria. Am J Respir Crit Care Med 2007;176:208–213.[Abstract/Free Full Text]
2. Compston JE. Vitamin D deficiency: time for action. Evidence supports routine supplementation for elderly people and others at risk. BMJ 1998;317:1466–1467.[Free Full Text]
3. Dawson-Hughes B, Heaney RP, Holick MF, Lips P, Meunier PJ, Vieth R. Estimates of optimal vitamin D status. Osteoporos Int 2005;16:713–716.[CrossRef][Medline]
4. Lips P. Vitamin D status and nutrition in Europe and Asia. J Steroid Biochem Mol Biol 2007;103:620–625.[CrossRef][Medline]

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