Increasing vitamin D intake -- or getting more sun, which can spur the body to produce it -- may help lower the risk of stroke, according to new research from UAB.
The findings come from two studies presented today at the American Stroke Association International Stroke Conference in New Orleans. Both could lead to new insights on why strokes have previously been linked to extreme temperatures.
Researchers from the University of Alabama at Birmingham planned to make several presentations at the conference, including studies showing a link between poverty and stroke and that rural residents have a higher risk of stroke death. Most were drawn from the massive REGARDS study -- it stands for Reasons for Geographical and Regional Differences in Stroke, a national cohort of more than 30,000 people signed up between 2003 and 2007. The study is funded by the National Institutes of Health and housed at UAB and several other institutions.
Study author Suzanne Judd and others looked at Vitamin D, which was already linked to Alzheimer's and Parkinson's diseases, dementia, stroke, hypertension and diabetes.
They followed 26,039 people for an average of five years, tracking what they ate and figuring how much vitamin D they absorbed from food and supplements. Those who ate the most vitamin D -- between 382 and 1,774 international units a day -- had an 11 percent lower risk of stroke and a 24 percent lower risk of cognitive impairment compared with those who ate less than 53.1 IU/day. The recommended daily allowance is 600 IU for people older than 1 and younger than 70.
"Vitamin D has a lot of effects in the body," Judd said. "It lowers inflammation. It also acts as a blood pressure reductant,<CM+NT cq -NT> so it could be somehow having an effect on stroke that way."
And while some people struggle to take in about 600 IU a day through food, just 10 minutes in the sun in Birmingham in the spring or summer could provide residents with thousands of IU of the vitamin.
That could explain why people with less exposure to sunlight have higher risk of stroke, said Leslie McClure, one of the authors of the second study.
That research used data from NASA satellites to calculate how much sunlight 16,529 REGARDS participants received. People exposed to the highest and lowest temperatures had the highest risk of stroke, as did those who had the lowest average monthly sun exposure.
"We basically confirmed what others have shown (about temperature), but the sunlight is a new association," McClure said.
Both topics require more research, the authors said. Judd's team is already applying for funding that will let it test participants' blood for vitamin D, and McClure said the biology behind sun and stroke isn't clear, though she does recommend that people get about 10 minutes of exposure a day to their arms and legs without sunscreen.
But there could be some insight as to why the South -- where we stay inside in the summer and slather on D-blocking sunscreen -- has been named the "stroke belt." The fact that it's tougher to exercise outside in the heat may also weigh in, since inactivity, obesity and high blood pressure are also factors in stroke.
"Trying to disentangle this is really what REGARDS is all about," McClure said.