In a finding that surprised and puzzled researchers, a new study shows that low levels of vitamin D double the risk of dying of a fatal stroke in whites but not in African Americans.
Because darker skin blocks more of the sun's rays, African Americans are more likely than whites to be deficient in vitamin D. Researchers at Johns Hopkins thought low levels of vitamin D might help explain why African Americans have a higher risk of stroke than whites.
The team analyzed the health records and vitamin D levels of nearly 8,000 black and white adults with no history of heart attack or stroke, using data collected between 1988 and 1994. They followed the participants, who were enrolled in a long-running national study, for an average of 14 years. They then looked at the number of fatal strokes.
"Stroke is more common in blacks than whites," says Erin Michos, M.D., lead author of the study. But even adjusting for their higher rates of hypertension and diabetes, blacks have higher rates of stroke. "So we thought that since blacks also have lower levels of vitamin D, that might cause the excess risk," she continues. "Much to our surprise, we found no relationship between low levels of vitamin D and death from stroke in blacks."
The study had some important limitations. It looked only at fatal stroke, which happened infrequently, according to Michos. In addition, vitamin D levels, which fluctuate, were measured only once by a blood test so they may not have reflected lifetime patterns.
Stroke is the nation's number three cause of death, so Michos says it's important to at least consider low vitamin D as a risk factor for stroke in whites.
The Johns Hopkins team presented its findings this week in Chicago at the annual Scientific Sessions of the American Heart Association, where several other new studies on vitamin D produced intriguing results, including:
- Living longer and healthier with vitamin D
Vitamin D deficiency has been linked to high blood pressure, type 2 diabetes, heart attack and heart failure. But a new study reports that people with low levels of D also had less of a chance of surviving these diseases when they got them. University of Kansas researchers looked at the records of more than 10,000 people, average age 58, who had either normal or low vitamin D levels. Importantly, the researchers found when those with low levels were given added vitamin D, they lived longer.
- Vitamin D and blood pressure
Low levels of vitamin D are associated with prehypertension, borderline high blood pressure.
Researchers at West Virginia University looked at the records of more than 9,000 men and women — who did not suffer from high blood pressure — to determine their vitamin D levels. They found that lower levels of D were associated with prehypertension independent of smoking, weight, cholesterol levels, type 2 diabetes and physical inactivity.
The next step will be to establish whether increasing the levels of vitamin D can block the development of full blown high blood pressure.
Nissa Simon, who lives in New Haven, Conn., writes about nutrition and medical issues.