Outdoor heat has been associated with increased mortality and increases in COPD hospitalizations, say researchers.

People with chronic obstructive pulmonary disease (COPD) may experience fewer symptoms and better overall health if they stay out of the heat this summer, according to a new study.

Conducted by researchers at Johns Hopkins University and presented at the 2014 American Thoracic Society International Conference, the study found that COPD patients exposed to warm indoor temperatures “had greater disease-related morbidity, including an increase in symptoms, a rise in the use of rescue medications, and a decline in lung function.” Outdoor heat exposure was also associated with increased COPD symptoms, researchers said.

COPD is a term used to describe a wide range of progressive lung diseases, often caused by smoking, second-hand smoke, or other pollutants. According to the COPD Foundation, an estimated 24 million Americans have COPD.

“Understanding the effect of heat on susceptible populations is increasingly important to anticipate health effects related to climate change,” study authors wrote. “Outdoor heat has been associated with increased mortality and increases in COPD hospitalizations in population studies. Less is known about individual-level exposure to heat and the impact on disease-specific outcomes.”

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Researchers studied 84 former smokers with moderate to severe COPD throughout three one-week periods, with three months between each period. Participants were monitored daily during the observation periods and were asked to complete assessments of common COPD symptoms, including breathlessness, cough and sputum production, rescue-inhaler use, and lung function.

Researchers then looked at the time participants spent indoors and outdoors during the warm season in Baltimore, where the study took place. They defined “warm season” as the time between the first and last day of temperatures higher than 90 degrees Fahrenheit. The study included a total of 602 observation days, and participants reported going outdoors on just 48 percent of those days.

“Although participants spent most of their time indoors, outdoor temperature was associated with increased symptoms on days participants went outdoors,” according to the study authors.

However, outdoor heat exposure was not associated with medication use or lung function, the researchers said.

According to the study’s press release, these results remained the same even after researchers accounted for air-pollution concentrations.

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“The findings of clinically significant changes in disease-specific indicators of COPD morbidity support the need for adaptive approaches to protect such individuals from adverse respiratory health effects of heat exposure,” the study authors wrote.

“Future work is needed to understand the mechanism by which heat impacts individuals with COPD and to identify the most effective intervention strategies,” said lead study author Meredith McCormack, M.D., MHS, in a press release. “The need for novel approaches is especially critical in the face of anticipated climate change.”

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