ORLANDO—Vitamin D supplementation may reduce blood pressure (BP) in African-American patients with hypertension in a dose-dependent manner, regardless of the intensity of antihypertensive treatment, researchers announced at the American Heart Association Scientific Sessions 2011.

“The findings, if confirmed in future studies, will have huge therapeutic and public health implications because vitamin D can potentially be a very useful adjunct to conventional antihypertensive treatment,” John Flack, MD, Chairman of the Department of Internal Medicine at Wayne State University in Detroit, told Renal & Urology News.  

For the study, the investigators examined the longitudinal relationship between vitamin D supplementation and BP change and control independent of antihypertensive drug treatment intensity in a largely African-American referral hypertensive cohort. African-Americans have a high prevalence of vitamin D deficiency and hypertension.

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While vitamin D levels have repeatedly been shown to correlate inversely with blood pressure and hypertension risk both in cross-sectional and prospective epidemiological studies, previously reported vitamin D supplementation studies have been “mostly but not exclusively” negative, Dr. Flack pointed out.

He was quick to emphasize, however, that the earlier studies have not typically required randomized participants to have vitamin D deficiency (defined as a vitamin D level 20 ng/mL or less) or hypertension and they have also used relatively low levels of vitamin D ingestion (1000 IU/day or less).

The present study included 648 patients with a mean baseline blood pressure of 156/92 mm Hg, and a mean baseline serum vitamin D level of 17.6 ng/mL, about two thirds of whom were women. The median duration of follow-up was 10.6 months, or five clinic visits.

Results showed that subjects who ingested 2000 IU/day or more of vitamin D had a BP reduction of 10/7 mm Hg. Subjects who took less than 2000 IU/day had a BP reduction of 4/3 mmHg.

Overall, the BP-lowering effect was most pronounced at vitamin D doses of 2000 IU/day or higher in those with baseline serum vitamin D levels of 15 ng/mL or less. 

The findings are consistent with two positive randomized trials of vitamin D supplementation for BP lowering on multiple counts, Dr. Flack said. The three studies had similar prospective BP reductions with vitamin D supplementation. In addition, in all three studies, those individuals with the lowest baseline vitamin D levels who received higher levels of supplementation also had the largest BP reductions. Additionally, in all three studies, vitamin D had a more marked effect on systolic than diastolic blood pressure.

“To our knowledge, ours is the largest prospective report of the blood pressure response to vitamin D supplementation in African-Americans,” Dr. Flack said.  “Though generalizability to the broader population is limited, our results are strengthened by the fact that we followed a high-risk cohort and had a relatively long period of follow-up and used relatively high daily doses of vitamin D.”

Potential limitations, he added, include the study’s non-randomized design. Further, residual confounding, despite the inclusion of multiple potential confounding variables, may have influenced the results.

Finally, he said that the findings apply mostly to black hypertensives, especially women, given the demographic composition of the study cohort.