A vitamin D deficiency doubles the risk of fatal strokes in whites, but has no effect on the risk in blacks, even though blacks are more likely to have vitamin D deficiencies and are 65% more likely to die from strokes, researchers said Sunday. The results were puzzling, said Dr. Erin Michos of the Johns Hopkins School of Medicine in Baltimore. "We thought maybe the lower vitamin D levels might actually explain why blacks have higher risks for strokes," she said.
Stroke is the third leading cause of death in the United States, killing more than 140,000 Americans annually and permanently disabling more than half a million.
Vitamin D, a fat-soluble vitamin involved in bone health, helps prevent rickets in children, protects against severe bone loss in adults, and may lower the risk of heart disese, cancer, multiple sclerosis, diabetes and other medical conditions. Natural sources include exposure to ultraviolet B rays in sunlight and eating fatty fish, egg yolk, and fortified foods such as milk and breakfast cereals.
Michos and her colleagues analyzed health records of 7,981 black and white adults who participated in the Third National Health and Nutrition Examination Survey of Americans, conducted between 1988 and 1994, following the participants for a median of 14 years. They reported at a Chicago meeting of the American Heart Assn. that, among the participants, 6.6% of whites and 32.3% of blacks had severely low levels of vitamin D in their blood, classified as levels below 15 nanograms per milliliter. During the period of the study, 116 whites and 60 blacks died of stroke. Accounting for age and other risk factors, blacks were 65% more likely to suffer a stroke. Higher levels of diabetes and hypertension probably account for some of the increased risk, but not this much, Michos said. "Something else is surely behind this problem. However, don't blame vitamin D deficits."
The lack of sensitivity to low levels of vitamin D may be an adaptation to historic low levels associated with the sun-blocking effects of skin pigments, she added. The blacks in the study also had fewer incidents of bone fracture and greater overall bone density than whites. "In blacks, we may not need to raise vitamin D levels to the same level as in whites to minimize their risk of stroke," she concluded.