By Chris Kaiser, Cardiology Editor, MedPage Today
Published: February 03, 2012
Reviewed by Zalman S. Agus, MD; Emeritus Professor
University of Pennsylvania School of Medicine and Dorothy Caputo, MA, RN, BC-ADM, CDE, Nurse Planner
NEW ORLEANS – Too much sunlight is bad for the skin, but not enough may be a risk factor for stroke, according to a study presented here at the American Stroke Association's International Stroke Conference.
Of the more than 16,000 black and white patients followed, those who lived in areas that had shorter exposure to sunlight had a 56% increased risk of stroke, Leslie McClure, PhD, from the University of Alabama at Birmingham, Ala., and colleagues found.
Interestingly, the protective benefit of sunlight was virtually eliminated in the Southeastern stroke belt and buckle, which comprises parts of the coastal plains of Georgia as well as North and South Carolina, McClure told MedPage Today.
“How do we resolve this paradox that increased sunlight leads to decreased stroke risk, but in the stroke belt where there is lots of sunlight, there is also an increase of stroke?” McClure asked.
The investigators obtained data from 16,529 participants in the REGARDS (Reasons for Geographic and Racial Differences in Stroke) study who were 45 years or older. The participants were interviewed at baseline and surveyed every six months for cardiovascular disease incidence. They also filled out a self-administered questionnaire for residential histories since birth. The average follow-up was five years.
Researchers used sophisticated satellite and ground monitor technology from NASA to calculate sunlight exposure and temperature. They matched these variables to geography and weighted them for the duration at each residential location.
Even after McClure and colleagues controlled for factors such as age, race, education, systolic blood pressure, region, gender, income, physical activity, time spent watching TV, and body mass index, they still found that lack of sunlight exposure and lower temperatures were associated with a risk of stroke. Extreme temperatures also were linked to an increased stroke risk.
“The sun gets a bad rap, but sensible sun exposure is probably the way to go,” McClure said.
The study was limited by unmeasured confounders such as air pollution, a single rather than repeated measures of exposures, and potential exposure misclassification.
McClure concluded that the mechanism through which sunlight exposure is related to stroke still needs to be explored. Her colleagues explored one such possibility: Vitamin D exposure.
Vitamin D and Stroke
In their Vitamin D study, researchers found that those with a higher level of vitamin D in their diet had a decreased risk of stroke and cognitive impairment.
Similar to the previous study, Suzanne E. Judd, PhD, from the University of Alabama in Birmingham, and colleagues surveyed roughly 21,400 black and white participants in the REGARDS study every six months for five years to assess the incidence of strokes and cognitive functioning declines. The mean age was 65.
The investigators measured vitamin D by using a food frequency questionnaire. Participants were asked once to give an average dietary intake for a year. Vitamin D supplements also counted toward total intake.
“As people age, their skin loses the ability to make the precursor of vitamin D,” Judd told MedPage Today. “In addition, African Americans have a harder time making vitamin D. Consequently, we hypothesized that dietary vitamin D levels might be a good proxy for blood levels in the elderly and in blacks.”
Judd and colleagues found that those with higher levels of vitamin D in their diets, when compared with those with lower levels, had an 11% reduction in stroke and a 24% reduction in cognitive impairment after adjustment for age, race, income, education, hypertension, diabetes, high cholesterol, heart disease history, and weight. There was no difference between blacks and whites. However, the 95% confidence intervals (four adjusted models) were fairly wide for the stroke risk.
“There is some evidence that vitamin D is cardioprotective, and it has some role in blood pressure and inflammation. So it makes sense to ask whether vitamin D has protective properties for the brain,” Judd said.
In late 201o, the Institute of Medicine (IOM) released recommendations for vitamin D intake, but only as it related to bone health. The IOM had concluded after reviewing nearly 1,000 scientific studies that the evidence for vitamin D's role in reducing cancer, heart disease, and stroke was inconclusive.
The IOM called for more research. As well, Harvard investigators have begun the Vitamin D and Omega-3 Trial (VITAL). This study will involve 20,000 men and women across the U.S. who will be randomized to either vitamin D and fish oil supplements or to placebo.
Judd said the VITAL trial, as well as others like it, are needed to further evaluate the potential of vitamin D as a neuroprotectant.
The study was limited by a one-time assessment of vitamin D status. Also, Judd noted the association of vitamin D with reduced risk of stroke and cognitive impairment could be due to unmeasured confounders, such as that those with higher levels of vitamin D also might have healthier diets.
Both studies were funded by the National Institutes of Health/National Institute of Neurologic Disorders and Stroke.
Neither McClure nor Judd had financial conflicts to report.
— Last Edited by Greentea at 2012-02-14 19:37:22 —