People with dark skin, particularly those who live at higher latitudes, may have increased risk of heart disease and stroke because vitamin D, which is produced in the skin by exposure to sunlight, is reduced in the deeper pigmentation leading to a nutritional deficiency.

Dr. Kevin Fiscella, a professor at the University of Rochester, co-authored the new study published in the January/February issue of the Annals of Family Medicine. Fiscella, along with Dr. Peter Franks of the University of California-Davis, reviewed data on more than 15,000 American adults from the third National Health and Nutrition Survey, conducted from 1988 to 1994. They found that 25% of the adults with the lowest levels of vitamin D had a 40% higher risk of cardiovascular death.

The authors then studied the link between low vitamin D and race. African Americans had a 38% higher incidence of heart or stroke-related death than that of white Americans.

Low levels of vitamin D are associated with the development of high blood pressure, kidney disease, obesity, and diabetes. It is not yet known if supplementation of vitamin D to reverse the deficiency will also lower the risk of cardiovascular disease. "We don't truly know the answer," Fiscella said. "That is the really pivotal question, what happens to cardiovascular risk if you correct blood levels of vitamin D. We do know that small supplements for middle-aged people don't seem to have any effect."

The current recommended daily intake of vitamin D for adults up to age 70 is 400 IU. For older adults, 600 IU is the guideline because levels decline with age. Currently, the RDI’s do not distinguish a different intake based on race.

Based on recent studies that show that as many as 30-50% of the American population are deficient in vitamin D, some experts feel the RDI should be increased. Dr. James O’Keefe, director of preventive cardiology at the Mid-America Heart Institute in Kansas City recommends 2,000 IU a day for white American adults, and 4,000-5,000 for African-Americans.

Twenty minutes of sunlight each day is recommended for optimal vitamin D production in whites. African Americans should aim for three to five times that much for adequate vitamin D. In addition to UVB exposure, vitamin D can also be found in fortified dairy foods and vitamin supplements.