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Published: Apr 11, 2013
By Crystal Phend , Senior Staff Writer, MedPage Today
Action Points
- Blacks have higher rates of hypertension than whites in the U.S. and also have lower circulating levels of 25(OH)D.
- In this study, 3 months of vitamin D supplementation had a small to modest effect to lower systolic blood pressure.
Vitamin D supplements may modestly lower blood pressure for black adults, a clinical trial showed.
Systolic pressure fell by 1.4 mmHg more per 1,000 international units of cholecalciferol given per day than with placebo over a 3-month period (P=0.04), John P. Forman, MD, MSc, of the Brigham and Women’s Hospital’s Kidney Clinical Research Institute in Boston, and colleagues found.
That impact lost statistical significance after adjusting for baseline blood pressure, the group reported in the April issue ofHypertension.
However, the 0.2-mmHg greater reduction in systolic pressure per 1-ng/mL in plasma 25(OH)D levels remained significant, “supporting a true causal association.”
Larger, longer studies are needed to confirm an effect, Forman’s group cautioned.
But if confirmed, boosting vitamin D could be a good avenue to reduce blood pressure or prevent hypertension in this population, which has higher prevalence of hypertension but lower circulating vitamin D levels than reported in whites, the group suggested.
The best-supported mechanism for vitamin D to impact blood pressure is via downregulating the renin-angiotensin system, which is believed to be a stronger mediator of blood pressure among blacks, they explained.
Vitamin D supplement trials have had mixed blood pressure results but included relatively few black participants.
So Forman’s group conducted a randomized trial in an exclusively black cohort drawn from a community-based colorectal cancer prevention study, community and faith-based organizations, and a refer-a-friend program.
The 250 participants with follow-up through the 3 months of treatment had been randomized double-blind to placebo or one of three doses of cholecalciferol (vitamin D3): 1,000, 2,000 or 4,000 IU daily.
Treatment started in early winter to control for major seasonal differences in sunlight-derived vitamin D.
Vitamin D levels rose in a dose-dependent manner as expected and then declined after the end of active treatment to 6 months, although remaining higher than baseline.
The change in systolic blood pressure over 3 months was:
- An increase of 1.7 mmHg on placebo
- A decline of 0.66 mmHg with 1,000 IU of cholecalciferol per day
- A decrease of 3.4 mmHg with 2000 IU per day
- A drop of 4.0 mmHg with 4,000 IU per day
Supplement dose didn’t show a durable impact at 6 months, but the higher serum levels over the longer run appeared to have a persistent benefit on blood pressure.
Each 1-ng/mL higher 25-hydroxyvitamin D at month six compared with baseline remained associated with a 0.2-mmHg lower systolic pressure, albeit of borderline significance atP=0.05.
No significant impacts were seen on diastolic blood pressure at any point.
In a sensitivity analysis excluding the 42% of participants taking antihypertensive medications, results were similar but not significant (-1.2 mmHg per 1,000 IU/day, P=0.24), “possibly owing to the restricted sample size.”
The effect was similar for those with a blood pressure above 120 mmHg as for those below that threshold (median was 122/78 mmHg).
While the treatment groups didn’t differ significantly at baseline in blood pressure, the highest vitamin D dose group did have what would be considered a clinically significantly higher systolic pressure, which raised the possibility that part of the effect was due to regression to the mean.
After adjustment for baseline, each 1,000 IU cholecalciferol per day was associated with only a 0.7 mmHg decline in systolic pressure compared with placebo, which wasn’t statistically significant at P=0.29.
The researchers cautioned that 3 months may not have been long enough to fully assess the effect of vitamin D on blood pressure and that antihypertensive medications could have masked the impact of vitamin D supplements.
The trial was funded by the National Heart, Lung and Blood Institute, the National Cancer Institute, the Department of Defense Prostate Cancer Research Program, the American Society of Clinical Oncology Career Development Award, and Pharmavite.
The authors did not report conflicts of interest.
Primary source: Hypertension