The research: Yale University investigators cross-referenced local temperature and dew point data with 134,510 ischemic stroke hospitalizations taken from the Nationwide Inpatient Sample Database. They found that days with extreme temperature and dew point fluctuations yielded higher incidence of stroke hospitalization—regardless of region, season, or patient factors like high blood pressure or diabetes. Stroke occurs when blood flow to a part of the brain stops. What it means: Whether it’s very cold or very hot, humid weather can cause significant stress on the body. As blood vessels work to adapt to quick, extreme temperature changes, blood pressure and blood clotting speeds can be affected and increase the risk for stroke, says lead researcher Judith H. Lichtman, PhD, an associate professor at the Yale School of Public Health. But it’s not a one-forecast-fits-all scenario: Rather than a specific high or low temperature creating a bigger stroke danger for everyone, “it’s about how your body may be adjusting to the changes where you live,” Dr. Lichtman says.  The bottom line: We often think of things like blood pressure and cholesterol levels as predictors of stroke, but the environment may be another important factor. And though it’s impossible to control polar vortexes or heat waves, we can be more aware of the risks posed by rapid temperature swings. “We can’t ignore the fact that more extreme weather challenges our bodies,” Dr. Lichtman says. “We have to be aware that under extreme temperature conditions, we should be more vigilant in looking for signs of stroke in ourselves and in our loved ones.” Here’s what you need to know about the signs and symptoms of stroke.  More from Prevention: 9 Ways To Never Have A Stroke