A possible role for vitamin D deficiency in contributing to the winter increase in cardiovascular disease mortality was investigated by testing the effect of vitamin D supplementation on blood pressure and other cardiovascular risk factors during winter.
Randomised double-blind trial of vitamin D supplementation in winter.
Men and women, mean age 70 years (range 63-76) recruited from general practitioner age-sex registers in Cambridge (UK).
95 people received a single oral dose of 2.5 mg cholecalciferol and 94 received the placebo at baseline interviews during December 1991. Follow-up assessment was 5 weeks later during January 1992.
Comparing follow-up with baseline assessment, serum 25-hydroxyvitamin D increased in the treated group and decreased slightly in the placebo group [mean (s.d.) change: 7.2 (+/- 3.8) vs -1.4 (+/- 1.1) ng/ml, P = 0.0001]; while parathyroid hormone decreased in the treated, and increased in the placebo, group [-0.27 (+/- 0.78) vs 0.13 (+/- 0.75) pmol/l, P = 0.0004]. However, the mean change in blood pressure was similar in both groups: systolic -5 (+/- 13) vs -5 (+/- 16) mmHg, P = 0.81; diastolic -1 (+/- 9) vs -1 (+/- 9), P = 0.92; as was the mean change in serum cholesterol [-0.07 (+/- 0.52) vs -0.05 (+/- 0.60) mmol/l, P = 0.81]. In contrast, the mean change in radial pulse was significantly decreased in the treated group compared with placebo [-2 (+/- 9) vs 1 (+/- 7) beats per min, P = 0.030].
The failure of vitamin D supplementation to change blood pressure or serum cholesterol suggests that the winter increase in these factors is not caused by decreased vitamin D levels.