US researchers investigating the disparity between blacks and whites in heart and stroke-related deaths have suggested that vitamin D deficiency may be partly responsible.

The National Heart Lung and Blood Institute funded study was led by Dr Kevin Fiscella of the University of Rochester Medical Center (URMC), New York, and is to appear in the January-February 2010 issue of the journal Annals of Family Medicine, which goes online on 11 January.

Fiscella is a national expert on disparities in health care and a professor of Family Medicine and Community and Preventive Medicine at URMC.

He and his colleagues decided to investigate vitamin D because there is growing evidence that low levels of the vitamin in the bloodstream is linked to diabetes, high blood pressure, kidney disease, heart disease, and other serious illnesses.

For the study, they looked at data on more than 15,000 American adults, including measurements of blood levels of vitamin D and death rates due to cardiovascular disease.

They also looked at other cardiovascular health factors such as BMI (body mass index), smoking status and levels of C-reactive protein (a measure of inflammation in the body).

Vitamin D gets into our bodies through diet, exposure to the sun and from supplements. The liver converts it to 25 hydroxyvitamin D or 25(OH) D, which is what is measured by a blood test.

Vitamin D deficiency is usually defined as having less than 20 nanograms per milliliter, with 30 ng/ml regarded as sufficient. The mean blood level among the participants in this study was 29.5 ng/ml.

The researchers also found that:

  • Deficiency in vitamin D was linked to higher rates of death among all participants.
  • Those most deficient in vitamin D had a 40 per cent higher risk of death from cardiac illness.
  • Adjsuting for race showed that blacks had a 38 per cent higher risk of death than whites.
  • However, this risk of death went down as vitamin D levels went up.
  • Adjusting for poverty had a similar effect.

The authors said these findings suggest that vitamin D may be a modifiable, independent risk factor for heart disease, and that vitamin D and poverty exert separate effects.

Commenting on the disparity between blacks and whites, Fiscella said there was a complex host of genetic and lifestyle factors among blacks that might explain why they have lower vitamin D levels across the lifespan compared to other races.

Some black people have genetic factors that stop vitamin D being absorbed efficiently. One of these is higher lactose intolerance, which has an indirect effect in that people with this factor tend to exclude vitamin-enriched milk from their diet. Another is having darker skin pigment, which significantly reduces the amount of vitamin D made in the body.

Fiscella said that the findings suggest:

“The next step would be to intervene to boost vitamin D levels safely, with supplements.”

In September 2009, a review article in The American Journal of Medicine pointed out that vitamin D deficiency was a global health problem, occurring in about 36 per cent of otherwise healthy adult Americans and 57 per cent of general medicine hospitalized patients.

Most of the tissue and cells in our bodies have receptors for vitamin D: it plays a key role in controlling cell activity and growth. Deficiency in vitamin D helps cause inflammation associated with heart disease, cancer and bone illnesses.

Fiscella urged caution in interpreting these findings without a doing proper trial, however. This is an observational study and not a controlled clinical trial: some findings from observational studies don’t bear out in clinical trials, as certain studies on links between vitamin E and beta-carotene and poor heart health have shown.

However, Fiscella said the evidence here was convincing enough to warrant further investigation of the potential link between vitamin D and heart disease, particularly among blacks.

Annals of Family Medicine

Source: UMRC News.

Written by: Catharine Paddock, PhD