Danger in Shifting Summer Temperatures

Summer temperatures that spike up and down may boost the risk of death in older people who have long-term illnesses, a new study suggests.

Most people get used to the temperatures where they live, whether cold Connecticut or muggy Mississippi. When summer heat waves strike, death rates can climb for at-risk people, such as those who are very young, very old or ill. But scientists have been unsure about the effects of sudden temperature changes. Climate models predict that big day-to-day shifts in summer temperatures may become more common.

To take a closer look, NIH-funded scientists analyzed Medicare data on more than 3.7 million at-risk people, ages 65 and older, in 135 U.S. cities. All had been released after hospitalization for a long-term illness, such as diabetes or a heart attack. Patients were tracked for up to 21 years.

The scientists found that greater swings in summer temperatures were linked to shorter survival. The link between temperature shifts and death was especially strong in those 75 and older. Survival times were longer in cities with higher proportions of green space, including parks and tree-filled areas. Shorter survival times were seen in densely populated cities.

“We found that, independent of heat waves, high day-to-day variability in summer temperatures shortens life expectancy,” says Dr. Antonella Zanobetti of the Harvard School of Public Health. “This variability can be harmful for susceptible people.”