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.