Vitamin D: Ten Beliefs

Abstract

What the authors failed to realize is that many of the clinical trials were based on the guidelines for pharmaceutical drugs. Such trials have two main assumptions: (1) that the trial is the only source of the agent and (2) that there is a linear doseresponse relation. Neither assumption is satisfied for vitamin D trials. Heaney recently outlined the guidelines for trials of nutrients such as vitamin D.2 They include that the baseline 25-hydroxyvitamin D [25(OH)D] concentration should be measured, only those with low concentrations should be enrolled in the study, sufficient vitamin D should be given to raise concentrations to achieve significant reductions in the risk of health outcomes, and the achieved concentration should be measured. In addition, meta-analyses should only compare trials with similar conditions. A typical 25(OH)D concentration-health outcome relation is given for breast cancer in Figure 2 in a recent paper.3 Risk decreases rapidly from 10 to 30 nmol/l, at a moderate rate from 30 to 60 nmol/l and slowly above 60 nmol/l. The percentile values of 25(OH)D concentrations for women aged over 50 years in the US for [2001][2002][2003][2004][2005][2006] 4 can be used with the 25(OH)D-breast cancer incidence relation to estimate the reduction in breast cancer rates if all women achieved 100 nmol/ l, which could take about 4000 IU/day vitamin D 3 . The result is a 35 % reduction. This value compares well with the results from the Women's Health Initiative for those women not taking vitamin D or calcium prior to enrollment: taking 1500 mg/day calcium plus 400 IU/day vitamin D 3 by them significantly decreased the risk of total, breast and invasive breast cancers by 14-20 %.