Extreme and prolonged heat waves have long been linked to an increased risk of hospitalizations and deaths from cardiovascular disease events like heart attacks and strokes, particularly in regions of the world where temperatures are typically milder. But much of this research has been inconclusive about how age and sex influence the odds of these heart-related deaths. For the new study, researchers examined 15 years of data on 39,912 heart-related summertime deaths among men and women in England and Wales and 488 similar fatalities among U.S. men in the Seattle metropolitan area. These places are at parallel latitudes, with comparable climates and similarly low usage of residential air-conditioning, the study team noted. RELATED: Hydration Calculator: How Much Water Do You Need to Drink a Day? Scientists also looked at historical meteorological data to identify summer heat waves when temperatures climbed above historical averages. In the United Kingdom, each 1 degree Celsius (1.8 degrees Fahrenheit) increase above typical summer nighttime temperatures was associated with a 3.1 percent higher risk of heart-related deaths among men 60 to 64 years old. Hotter nights didn’t appear to change the odds of these fatalities among women or older men, however. For the U.S. cohort, each 1 degree Celsius spike in temperatures on summer nights was linked to a 4.8 percent higher risk of heart-related deaths among men 65 and under. Older men, however, didn’t appear to have a greater risk as temperatures rose. “Considering the growing likelihood of extreme summers in western USA and UK, our results invite preventive population health initiatives and novel urban policies aimed at reducing future risk of cardiovascular disease events,” the researchers wrote in their article in BMJ Open, published March 28. One limitation of the study is that researchers lacked the data necessary to determine if the risk of heart-related deaths was worse during heat waves in urban areas. Some previous research suggested that heat waves disproportionately impact city dwellers because the population density, miles of asphalt, and canyons created by tall buildings can create so-called “heat islands” where already hot temperatures soar even higher. The study also wasn’t a controlled experiment designed to prove whether or how extreme heat might directly cause fatal heart attacks, strokes, or other cardiovascular-disease-related events. It’s also not clear from the study why heat waves appeared to impact only men in their early sixties. “We hesitate to conclude from our analysis that only men are at risk,” says a coauthor of the study, Haris Majeed, a global and planetary health researcher at the University of Toronto. “We would require further data incorporating a much larger study population to study this.” It’s possible that these heart-related deaths are happening at least in part because heat waves make it hard to sleep, the study team writes. Dehydration and disrupted sleep can increase the risk of heart attacks and strokes, especially in people with underlying heart disease, Majeed says. “Dehydration could reduce blood volume and increase the risk of clotting,” Majeed adds. “And, sleep deprivation, whether due to heat, noise, or air pollution if windows are kept open, could also be stressful.” People can’t control the weather, but they can take steps to minimize the chance that a heat wave will give them a heart attack. “Just be sensible,” Majeed advises. “During heat waves: hydrate, stay cool, and avoid direct exposure to sunlight as well as excessive sweating. Those with known heart disease should be particularly cautious and follow the advice of their physician.”
