If You’re Hot, Cold And Then Hot Again, Your Life’s In Danger

If you live in an area where the temperature varies greatly, hot days followed by cool spells followed by a heat wave, those fluctuations may be shortening your life expectancy.

New research from Harvard School of Public Health (HSPH) suggests that seemingly small changes in summer temperature swings — as little as 1° Centigrade (about 2° Fahrenheit) more than usual — may shorten life expectancy for elderly people with chronic medical conditions, and could result in thousands of additional deaths each year. While previous studies have focused on the short-term effects of heat waves, this is the first study to examine the longer-term effects of climate change on life expectancy.

“The effect of temperature patterns on long-term mortality has not been clear to this point. We found that, independent of heat waves, high day to day variability in summer temperatures shortens life expectancy,” says researcher Antonella Zanobetti with HSPH. “This variability can be harmful for susceptible people.”

The study found that, within each city, when the summer temperature swings were larger the death rates climbed. Each 1°C increase in summer temperature variability increased the death rate for elderly with chronic conditions between 2.8 percent and 4 percent, depending on the condition. Mortality risk increased 4 percent for those with diabetes, 3.8 percent for those who’d had a previous heart attack, 3.7 percent for those with chronic lung disease, and 2.8 percent or those with heart failure. Based on these increases in mortality risk, the researchers estimate that greater summer temperature variability in the U.S. could result in more than 10,000 additional deaths per year.

“People adapt to the usual temperature in their city. That is why we don’t expect higher mortality rates in Miami than in Minneapolis, despite the higher temperatures,” says researcher Joel Schwartz, professor of environmental epidemiology at HSPH. “But people do not adapt as well to increased fluctuations around the usual temperature. That finding, combined with the increasing age of the population, the increasing prevalence of chronic conditions such as diabetes, and possible increases in temperature fluctuations due to climate change, means that this public health problem is likely to grow in importance in the future.”