The Women's Health Initiative Calcium/Vitamin D Trial.

The Women’s Health Initiative Calcium/Vitamin D Trial To the Editor: We appreciate the excellent review of research pertaining to vitamin D and hypertension by Vaidya and Forman in the recent issue of Hypertension.1 We agree with nearly all of their comments regarding the limitations of the Women’s Health Initiative Calcium/Vitamin D Trial regarding the effect of vitamin D supplementation on blood pressure (BP) and incident hypertension. However, we disagree with their final listed limitation that initiation of antihypertensive medication during follow-up was not taken into account in the analysis. In the analysis of incident hypertension, we excluded all of the women who had evidence of hypertension at trial enrollment (selfreported antihypertensive treatment, antihypertensive medication recorded in the medication inventory, or measured BP 140/ 90 mm Hg before randomization.) Trial participants received semiannual mailed questionnaires that inquired about initiation of antihypertensive medication, and BP was measured annually. Incident hypertension was defined as self-reported new antihypertensive treatment or measured BP 140/90 mm Hg after randomization. Thus, initiation of antihypertensive medication was taken into account, and there was no difference in incident hypertension between the calcium/vitamin D supplement and the placebo groups (hazard ratio: 1.01 [95% CI: 0.96 to 1.06]) There was also no difference between the groups in starting antihypertensive medications (hazard ratio: 1.04 [95% CI: 0.93 to 1.16]). In the analysis of BP change, which also did not differ between the treatment groups, there was no difference in antihypertensive treatment between the groups at randomization (28%).2 Because this was an intention-to-treat analysis of a randomized trial, we did not adjust for initiation of antihypertensive therapy, but it is highly unlikely that this would have differed between the 2 groups given the results described above for incident hypertension.