Modest swings in high temperatures can increase mortality risk

Extended heat waves, with sudden spikes in temperature that may last for more than a week, can be deadly, particularly for the elderly, whose bodies often do not respond to changes in temperature as well as younger people, health officials say.

But even the day-to-day fluctuations of summer temperatures above and below what is average for an area might shorten the life expectancy of older patients with chronic diseases, a recent study shows.

For every 1 degree Celsius increase in the day-to-day change in an area's average summer temperature, the death risk of the elderly with chronic conditions rose between 2.8% and 4%, depending on an individual's medical condition, according to the 24-year study published online April 9 in Proceedings of the National Academy of Sciences.

The study assessed year-to-year variations in the summer temperatures of 135 U.S. cities.

“People adapt to the usual temperatures in their city. … But people do not adapt as well to increased fluctuations around the usual temperature,” said senior author Joel Schwartz, PhD. He also is professor of environmental epidemiology at the Harvard School of Public Health in Boston.

Fluctuating summer temperatures can add stress to the heart and other organs as the body tries to regulate its internal temperature, said internist Gary Rogg, MD, assistant professor and assistant director of the Dept. of Medicine at Montefiore Medical Center in New York.

That process is further complicated among the elderly, who often take medication, such as beta blockers, that can impede sweat production and cause the body temperature to rise to unhealthy levels, said Georges Benjamin, MD, executive director of the American Public Health Assn.

“The effect of temperature patterns on long-term mortality has not been clear to this point,” said lead study author, Antonella Zanobetti, PhD. “We found that, independent of heat waves, high day-to-day variability in summer temperatures shortens life expectancy.” Zanobetti is a senior research scientist in the Dept. of Environmental Health at the Harvard School of Public Health.

Many scientists predict that temperature variability will become more common as carbon dioxide and other pollutants continue collecting in the Earth's atmosphere and trapping the sun's heat.

Data show that the average global temperature has increased at the fastest rate in recorded history during the past 50 years.

“We know that the Earth is continuing to get warmer, and there are a compilation of health issues that we're concerned about,” Dr. Benjamin said.

Between January and March, the average temperature of 42 degrees Fahrenheit in the contiguous United States was 6 degrees higher than the long-term average for this period, according to the National Oceanic and Atmospheric Administration.

March alone featured the warmest temperatures on record for that month since the agency began tracking the temperature in 1895.

For the Proceedings of the National Academy of Sciences study, researchers used Medicare data from 1985 to 2006 to follow the long-term health of 3.7 million chronically ill people older than 65 who lived in 135 U.S. cities. After adjusting for ozone levels within each city, they found that the years when the summer temperature swings were higher had more elevated death rates than the years with smaller fluctuations.

Risk increase factors

Mortality risk was highest for people with diabetes (4%) followed by those who had a previous myocardial infarction (3.8%), patients with chronic lung disease (3.7%) and those with heart failure (2.8%).

Based on those increases in mortality risk, the researchers estimate that greater summer temperature fluctuations in the U.S. could result in more than 10,000 additional deaths each year.

The mortality risk was as much as 2% higher for those living in poverty and for blacks, data show. Green space in cities lowered people's mortality risk.

These findings, “combined with the increasing age of the population, the increasing prevalence of chronic conditions 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,” Schwartz said.

To help prevent medical complications related to climate change among the nation's growing elderly population, Dr. Rogg encourages primary care physicians to remember to discuss with patients how to stay safe during the summer.

He recommends that doctors explain to such patients, “As we age, there are natural changes in the body that reduce the body's natural abilities to cope” with increased temperatures.

Dr. Benjamin recommends that doctors be familiar with which patients in their practices have chronic diseases and other issues, such as living alone, that raise the risk of developing heat-related health problems.

He encourages physicians to help those patients and their families create plans for how to handle modest temperature increases and heat waves. Such a plan could include making sure the individual has an air conditioner or windows that open, and enough water and medication to last three days in case of an emergency.

The American Medical Association has hosted state-based continuing medical education courses on climate change to ensure that physicians and other health professionals understand the rise in climate-related illnesses and injuries so they can prepare and respond to them. The Association also is promoting environmentally responsible practices that would reduce waste and energy consumption.