Letters

Disease Prevention: Vitamin D Trials

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Science  16 Nov 2012:
Vol. 338, Issue 6109, pp. 883
DOI: 10.1126/science.338.6109.883-c

Although there is a debate on cut-offs for appropriate vitamin D supplementation (“Uncertain verdict as vitamin D goes on trial,” K. Kupferschmidt, News, special section on Disease Prevention, 21 September, p. 1476), clinicians universally agree that vitamin D deficiency is detrimental for bone health (1). We also know that vitamin D overdosing can be toxic. What quantity will prevent both deficiency and toxicity?

To find the ultimate vitamin D dose and to evaluate its effectiveness, researchers should learn from randomized controlled trials (RCTs) of drugs for diabetic or hypertensive patients, who were usually treated with the goal of achieving well-defined targets, such as certain HbA1c or blood pressure levels. In the case of vitamin D, this would mean performing RCTs in individuals with overt vitamin D deficiency and using doses to achieve optimal vitamin D levels.

Instead of performing these kinds of RCTs, the design of the ongoing vitamin D trials resembles previous (disappointing) vitamin trials, which attempted to establish a dose that should fit for the entire population (2). If the current vitamin D trials fail, we will ask ourselves why we did not perform RCTs exclusively in vitamin D–deficient patients rather than attempting to base conclusions on a heterogeneous population. Subgroup analyses of existing trials will not satisfy health authorities.

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