We've heard many claims in the past decade — and much debate — about the role of vitamin D in the prevention and treatment of conditions as varied as brittle bones, heart disease, cancer, diabetes and dementia.
Now researchers at Brigham and Women's Hospital in Boston have what they think may be another tantalizing lead: Their study suggests moderate doses of vitamin D supplements might help reduce high blood pressure.
It was a small study in a particular group — roughly 250 African-American adults. "African-Americans have a much higher likelihood of being vitamin D deficient compared to other races, and also a higher likelihood of having high blood pressure," says nephrologist John Forman, who led the study.
The risks of high blood pressure are long-established. Among other complications, hypertension in some people is thought to double the risk of having a heart attack or stroke. Earlier studies in animals and people have hinted that vitamin D supplements might mitigate that cardiovascular risk for some.
Forman and his colleagues randomly divided their study's participants into four groups. One group took 1,000 international units of vitamin D a day, another group took 2,000 IU and another 4,000. The fourth group got a placebo; no one at the time knew which dose they'd been given. After three months of daily treatment, Forman checked everyone for changes in blood pressure.
"We found that vitamin D supplementation modestly but effectively lowered blood pressure," he says. "And people who were taking a placebo had a slight increase in their blood pressure."
Specifically, those taking the maximum dose — 4,000 IU per day — saw a four-point drop in their systolic blood pressure. That's the important top number in a blood pressure reading, and represents the force of the blood pushing against the arteries as the heart beats. Those taking lower doses of the vitamin experienced a smaller drop in blood pressure, and those who got the placebo saw a 1.7-point increase in systolic pressure.
Now, a four-point drop in blood pressure isn't huge. But if the effect holds up in bigger studies, Forman says, it might be important.
"If vitamin D does lower blood pressure in African-Americans, it can have a significant public health impact," Forman says, adding that the finding may apply to other racial groups, too.
The Brigham and Women's study wasn't designed to look into the physiology behind the effect, though Forman says vitamin D might ease constriction of blood vessels, or boost the kidneys' ability to rid the body of salt — another known risk factor for hypertension.
"We have been looking for reasons why vitamin D replacement seems to have a positive benefit in the cardiovascular arena," says Vincent Bufalino, a cardiologist and spokesman for the American Heart Association. "And now here we have some clear evidence it actually lowers blood pressure."
Does that mean everyone should rush to the pharmacy to buy vitamin D supplements? Not exactly, says Bufalino. Moderate doses in supplement form are benign, he says, and may be helpful for people whose blood levels of the vitamin are low. But first, check with your doctor, who may give you a blood test to see if you're truly deficient.
While we're waiting to see if the findings pan out in bigger studies, Bufalino says, there are already well-established steps that can ease wear and tear on arteries through changes in lifestyle.
"Lowering salt intake, caffeine, weight, [getting more] exercise — all [are] positive ways to impact blood pressure," he says.
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In Your Health today, strokes in young adults. But first, preventing one of the leading causes of stroke, high blood pressure. Over the past decade we've heard a lot of claims about the value of vitamin D, both pro and con. Well, now a new study suggests vitamin D supplements may help lower blood pressure among African-Americans.
NPR's Patti Neighmond reports.
PATTI NEIGHMOND, BYLINE: First off, this was a small study. Just 250 African-American adults. Dr. John Forman at Brigham and Women's Hospital in Boston headed the research.
DR. JOHN FORMAN: African-Americans have a much higher likelihood of being vitamin D deficient compared with other races, and also have a higher likelihood of having high blood pressure compared with other races.
NEIGHMOND: And high blood pressure doubles the risk of having a heart attack or stroke. Earlier studies in both animals and humans showed fewer heart attacks and strokes when Vitamin D supplements were taken.
Cardiologist Vince Bufalino is a spokesperson for the American Heart Association.
DR. VINCENT BUFALINO: We have been looking for reasons why vitamin D replacement seems to have a positive benefit in the cardiovascular arena. And here we now have some clear evidence that it actually lowers blood pressure.
NEIGHMOND: In the study, participants were divided into four groups. One took 1,000 units of Vitamin D a day; another, 2,000 units; and another, 4,000. The fourth group took a placebo. After three months, researcher Forman measured blood pressure to see if there were any changes.
FORMAN: We found that vitamin D supplementation modestly but significantly lowered blood pressure. And the people who were taking the placebo pill had a slight increase in their blood pressure.
NEIGHMOND: The highest dose of Vitamin D lowered systolic blood pressure by four points. Forman doesn't know exactly how vitamin D did this, but he says it may relax blood vessels so they don't constrict so much. It could also boost the kidneys' ability to rid the body of salt - a known risk factor for high blood pressure.
Now, a four-point drop in blood pressure isn't huge, but Forman says it's still beneficial.
FORMAN: If vitamin D does lower blood pressure in African-Americans, it could have a significant public health impact.
NEIGHMOND: There are other reasons why African-Americans suffer increased rates of hypertension. But if vitamin D helps even a little bit, it's worth looking at. And it's likely to offer some benefit to other racial groups as well.
Both Bufalino and Forman say lots more research needs to be done - larger studies with different racial groups. In the meantime, cardiologist Bufalino says lots of people have unexpectedly low levels of vitamin D. It's measured by a simple blood test. So he says it's a good idea to have your vitamin D levels checked. If they're low, Bufalino says, there's no harm in taking moderate doses of D supplements.
BUFALINO: You know, it has a positive influence; it's a benign treatment in that it's not some big toxic drug; and in fact, you know, it's beneficial together with lifestyle - again, lifestyle's still an effective way to lower blood pressure. Lowering your salt intake, lowering your caffeine intake, losing weight, exercise - all of those are positive ways to impact your blood pressure. And now vitamin D may be an additional helper to reduce your blood pressure.
NEIGHMOND: Does that mean you should race to the pharmacy to buy vitamin D supplements? Well, not exactly, says Bufalino. Check your levels with your doctor first. See if you need more vitamin D. And wait for the big studies to see if these preliminary findings pan out.
Patti Neighmond, NPR News. Transcript provided by NPR, Copyright NPR.