Lack of Sun Exposure and Vitamin D Linked to Stroke Risk
Vitamin D is produced by your skin in response to exposure to ultraviolet radiation from natural sunlight. A group of researchers at the University of Alabama conducted two studies that found that lack of both sun exposure and vitamin D may be risk factors for stroke.
Both studies were presented at the 2012 American Stroke Association's International Stroke Conference and used data from the Reasons for Geographic and Racial Differences in Stroke (REGARDS) study.
The first study examined 16,529 participants who were 45 years or older. In order to obtain personal history, the researchers distributed self-administered questionnaires. The participants were also interviewed at the onset of the study and then re-interviewed every six months for an average of five years to see if they suffered a cardiovascular incident.
Satellite and ground monitor technology from NASA was used to calculate average sun exposure and outdoor temperature for each participant. After controlling for a variety of lifestyle factors, the researchers found that lack of sun exposure and lower temperatures were directly correlated with higher stroke risk. Extreme temperatures were also correlated with higher stroke risk.
The researchers then conducted a study to determine if vitamin D could be one of the mechanisms behind the link between sun exposure and stroke risk. Approximately 21,400 participants with a mean age of 65 participated in the second study.
The participants were asked to estimate their yearly intake of vitamin D, including supplements. They were interviewed every six months for five years to assess the incidence of strokes and cognitive function declines.
Participants with the highest intake levels of vitamin D saw an 11% reduction in stroke risk compared to participants with the lowest intake levels. Additionally, they saw a 24% reduction in cognitive impairment risk compared to the lowest group.
The researchers concluded that sun exposure and vitamin D levels are both important risk factors for stroke. They recommend that people get a “sensible amount of sun exposure” in order to increase vitamin D levels and reduce the risk of stroke.