Threshold Effect for Vitamin D in CVD

BOSTONThere is an inverse association between low circulating vitamin D levels and risk of cardiovascular disease (CVD), but the effect is subject to a dosing threshold, according to researchers from Brigham and Women's Hospital, Boston. Their results were published Nov. 13 ahead of print in Circulation: Cardiovascular Quality and Outcomes, an American Heart Association (AHA) journal.

For their analysis, researchers searched MEDLINE and EMBASE from 1966 through February 2012 for prospective studies looking at the association of 25(OH)-vitamin D concentrations with risk of CVD. Of the 24 studies meting their inclusion criteria, 19 were factored into the meta-analysis; they involved almost 66,000 patients and more than 6,000 CVD. Comparing the lowest and highest vitamin D levels, they found a pooled relative risk of 1.52 (95% confidence interval, 1.30-1.77) for total CVD, 1.42 (95% confidence interval, 1.19-1.71) for CVD mortality, 1.38 (95% confidence interval, 1.21-1.57) for coronary heart disease, and 1.64 (95% confidence interval, 1.27-2.10) for stroke.

Looking at the linear nature of dose compared to risk for CVD, they discovered  CVD risk rose as the vitamin D level declined below 60 nmol/Lrelative risk was 1.03 per 25-nmol/L decrement in 25(OH)-vitamin D. However, CVD risk was not affected above 65 nmol/L doses, suggesting a threshold effect. Further, the association between vitamin D and CVD risk was greater in studies with fewer than 10 years of follow up.

They concluded, "Our meta-analysis of prospective observational studies allows an evaluation of the dose-response association between vitamin D and CVD risk over a broad range of vitamin-D levels, which will not only complement findings from ongoing randomized trials but also help to inform future trials that test the effect of vitamin-D supplements on CVD in terms of the optimal doses."

See also: Slide Show on 15 Reasons to Take Vitamin D