Rising temperatures increase health risks

Summer is almost here, and with it likely some blistering hot days. A recent study suggests the elderly should beware when the temperature spikes, because they face an increased risk of winding up in the emergency room short of breath on those days. And that's just a taste of what health problems to expect as global climate change cranks the heat up in many places.

Researchers for Johns Hopkins, Harvard and Yale universities reviewed a nationwide health database of 12.5 million older Americans on Medicare and found that increases in outdoor temperatures raise the risk for the elderly of being rushed to the hospital with respiratory disorders.


"All else being equal for the same time in summer, a day that's 10 degrees hotter will tend to have 4.3 percent more hospitalizations," said G. Brooke Anderson, the study's lead author and a postdoctoral biostatistics researcher at Hopkins' Bloomberg School of Public Health. The findings appeared in the March issue of the American Journal of Respiratory and Critical Care Medicine.

It's well-known that extreme heat can cause heat stroke and that the elderly are especially vulnerable. Maryland recorded 46 heat-related deaths last year, the majority in the Baltimore area and more than two thirds of them 61 years old or older.


But beyond those grim statistics, this study shows that for every person killed by extreme heat there are others whose health is jeopardized.

"It's pretty well recognized that that's just the tip of an iceberg, that high heat puts stress on people for a whole range of diseases," said Dr. John M. Balbus, senior adviser for public health with the National Institute for Environmental Health Sciences in Bethesda. This study, which received some of its funding from the institute, is one of the first to begin to quantify the role heat plays in causing or aggravating non-fatal health problems, Balbus said.

"It's pretty clear when somebody dies or comes in with heat stroke," he said. But it's less clear, he added, what role heat played when someone shows up in an emergency room with chronic obstructive pulmonary disease, a progressive disorder that makes it hard to breathe.

Anderson said she and her colleagues found higher hospitalizations on hot days nationwide, but the effect was more pronounced in the Pacific Northwest and other regions with cooler climates, compared with the South and other places that tend to be hotter anyway.

Anderson said there are at least a couple of possible explanations for the regional variations. People's bodies tend to adjust to constant heat after a while, she noted, by sweating at lower temperatures or making other metabolic changes. Routinely hot communities also tend to have more air-conditioned homes and buildings than cooler regions, she said, so they've got more shelter from it. Northern residents caught in a sudden heat snap may have fewer places to cool down.

Other research has found that air pollution — particularly summer smog, or ground-level ozone — can trigger breathing problems and even cause premature deaths among people with compromised health. Hot temperatures can cause potentially harmful higher ozone levels, but Anderson said researchers took the effects of air pollution into account and still saw an increase in hospitalizations linked solely to heat. They similarly looked at, but ruled out, the possibility that humidity rather than just heat sent more people to the ER. They saw similar increases with or without considering humidity, she explained.

Respiratory disorders are just one type of health problem that may be caused or worsened by hot temperatures. Next up, Anderson said, researchers are looking to see if heat is linked to an increase in hospitalizations for cardiovascular disease.

"It looks like there might actually be an increase in deaths, not necessarily an increase in hospitalizations," she said. That could be because heat may affect the heart differently than the airways.


With scientists projecting more heat waves from climate change, Anderson said, studies like theirs can help identify and explain resulting changes in people's health.

Such climate-related health shifts can have economic impacts. Balbus pointed out another study that has predicted that the risk of getting kidney stones, now highest in the Southeast, is likely to spread northward as average temperatures rise. Dehydration, a greater risk in hot places, can trigger the kidney blockages.

The number of cases of this painful condition could grow by up to 30 percent in some areas, the study said, and nationwide the cost, in terms of lost work as well as treatment, could exceed $1 billion a year.

"We see in these places that are hotter maybe we can adapt some," Anderson said. Researchers are still trying to tease out the various impacts, she added, "but from a global perspective I think there's pretty good evidence you could expect a health effect from heat waves in the future."