Vitamin D pills may help reduce blood pressure in blacks, a new study suggests. Many blacks have low blood levels of vitamin D. With darker skin, less sunlight is available for the body to use to make vitamin D. Blacks also are more likely to have high blood pressure than whites. The study included 250 African-American adults. They were randomly divided into 4 groups. Three of the groups received daily vitamin D pills, in different doses. The fourth group took placebo (fake) pills. Three months later, researchers checked their blood pressure. Systolic blood pressure had dropped by 4 millimeters of mercury (mmHg) for people taking the largest vitamin D dose, 4,000 international units (IU). It fell 3.4 mmHg for those taking 2,000 IU. The drop was 0.7 mmHg for the smallest dose, 1,000 IU. Systolic pressure rose 1.7 mmHg for those who got placebo pills. Systolic blood pressure is the first and larger number in a blood pressure reading. Diastolic pressure, the second number, did not change for any group in this study. The journal Hypertension published the study online. HealthDay News wrote about it March 8.

By Howard LeWine, M.D.
Harvard Medical School

What Is the Doctor's Reaction?

On average, blacks have lower blood levels of vitamin D than whites. But their risk of osteoporosis and related fractures is lower than the risk for whites.

The average blood level of vitamin D for blacks is 20 nanograms per milliliter (ng/ml). For whites, it is close to 30 ng/ml.

This has made it difficult for experts to define one normal value for vitamin D blood levels. For bone health, a vitamin D blood level of at least 20 ng/ml for an African American is probably fine. But for overall health, this might not be true.

Here's why. African Americans have a higher rate of high blood pressure than whites do. And they have increased risks of stroke, heart disease and kidney failure. Lower blood levels of vitamin D are linked with a greater chance of developing high blood pressure in all races.

Could this be one of the reasons that blacks have more high blood pressure (hypertension)? If so, could taking a vitamin D supplement help treat and maybe prevent high blood pressure in blacks?

Prior studies looking at this question have showed varying results. The journal Hypertension has just published results of a new study. It strongly suggests that vitamin D pills can help lower blood pressure in blacks diagnosed with high blood pressure.

The study is a randomized clinical trial. Randomized trials are considered the gold standard of medical studies. This type of study takes a group of people who are similar and randomly assigns them to one sort of treatment or another.

All the study participants were African Americans. They were randomly assigned to receive one of four daily supplements:

• Vitamin D, 1,000 international units (IU)
• Vitamin D, 2,000 IU
• Vitamin D, 4,000 IU
• An inactive pill (placebo)

The 3 groups that received vitamin D had lower blood pressure readings during the study than the group that received a placebo. The changes were modest. A higher dose of vitamin D appeared to lower blood pressure the most. But the extra drop in blood pressure between the 2,000 IU dose and the 4,000 IU dose was quite small.

What Changes Can I Make Now?

This one study does not provide enough evidence to say that African Americans with high blood pressure should take a vitamin D supplement. Nor should they take it to prevent high blood pressure.

But it surely is something very reasonable to consider. Darker skin produces much less vitamin D than lighter skin when exposed to sunlight. Black people require about 6 times the amount of ultraviolet light that whites need to produce similar blood levels of vitamin D. Melanin, the pigment that turns skin dark, absorbs the UV rays. Fewer UV rays reach the cells that make active vitamin D.

So blacks would need to spend much more time in the sun than is practical to raise vitamin D levels. Only a few foods provide natural vitamin D. Many doctors already suggest that all their patients of any skin color take a vitamin D supplement. According to the Institute of Medicine, up to 4,000 IU daily is safe.

I have been more conservative in my recommendation. I suggest that people take no more than 2,000 IU daily unless they have vitamin D deficiency. Back to the question, should an African American with high blood pressure take a vitamin D supplement? There is no official answer. Personally, I would say it is quite reasonable to take vitamin D3 at a dose of 2,000 IU daily.

What Can I Expect Looking to the Future?

You will see a lot more about vitamin D during the next few years. We know how important it is for bone health. Whether it plays a role in high blood pressure, heart and blood vessel diseases, and cancer risk still needs to be determined.