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Environmental Factor

Environmental Factor

Your Online Source for NIEHS News

May 2016

Who lives and dies in a hotter world, challenges for researchers

Joel Schwartz, Ph.D., discussed the challenges of studying direct effects of temperature, and impacts on different populations.

Temperature variability is a key factor affecting mortality associated with climate change, according to Joel Schwartz, Ph.D., from the Harvard T.H. Chan School of Public Health. Schwartz, who is also the director of the Harvard Center for Risk Analysis, discussed the challenges of studying direct effects of temperature and impacts on different populations.

His March 28 talk, “Who Will Live and Who Will Die: Temperature and Mortality in a Warming World” was part of the NIEHS Keystone Science Lecture Seminar Series.

The need for better models

Current models for studying physical responses to temperature change are not ideal, according to Schwartz. “We need to understand how the relationship between temperature and mortality changes as temperature changes,” he said.

“Temperature isn’t air pollution,” said Schwartz. “The dose-response curve really varies depending on the prevailing weather. People adapt.” Acclimatization, which is the process by which people gradually adjust to more extreme temperatures, is not addressed by most models, he pointed out.

Available temperature data also limits current models. Monitoring stations are frequently located at airports, so they may be far from where most people live and work, and may not account for the urban heat island effect. “I live in Boston,” said Schwartz. “The airport is on a peninsula sticking out into the Atlantic Ocean, where it is a lot warmer than I am in the winter, and cooler than I am in the summer.”

Furthermore, rural populations are under-studied, he said, because they live away from monitoring stations and away from the populous cities studied most frequently.

Certain populations will be especially vulnerable

Another challenge Schwartz highlighted is accounting for how temperature changes affect populations differently. Medical conditions such as Alzheimer’s disease, atrial fibrillation, or diabetes are associated with higher heat mortality. Schwartz also pointed to studies showing that socially disadvantaged populations face higher cardiovascular mortality on hot days.

Effects also vary by geographic region. Acclimatization depends on consistency, so in areas with variable temperatures people are less able to acclimate, compared to regions with consistently warmer or colder temperatures. “People adapt, but there’s probably some limit,” he said, explaining that beyond an annual summer mean temperature of about 77 degrees Fahrenheit, it appears that people do not acclimate.

For this reason, Schwartz explained, as temperatures in the U.S. increase, residents of the Northeast and Midwest may acclimate, and fewer people will die in heatwaves. However, the Southern U.S. may fare worse, with more heat-related mortality.

Key actions may help people adjust

Schwartz shared dose-response curves from studies showing that more people die during moderate heat days in cooler months than extreme heat days in summer months. “Our public health interventions for dealing with heat are focused on dealing with heatwaves, which is not where most of the deaths are,” said Schwartz. Adjusting heat warnings to account for this may reduce mortality, he suggested.

Another promising option is to increase the number of trees and the amount of green space, especially in urban areas. Schwartz pointed to data showing that such areas are associated with lower mortality, perhaps because green spaces help reduce high temperatures.

(Samantha Hall is a postbaccalaureate Cancer Research Training Award fellow in the National Cancer Institute Center for Cancer Research Laboratory of Toxicology and Toxicokinetics.)


Greenness around homes linked to lower mortality

By Virginia Guidry

Women live longer in areas with more green vegetation, according to new research funded by NIEHS and similar to that discussed by Schwartz. Women with the highest levels of vegetation, or greenness, near their homes had a 12 percent lower death rate compared to women with the lowest levels of vegetation near their homes. Analyses suggested that improved mental health, more social engagement, increased physical activity, and reduced air pollution contribute to the effect.

The study, conducted at the Harvard T.H. Chan School of Public Health and Brigham and Women’s Hospital in Boston, examined greenness around the homes of 108,630 women in the long-term Nurses’ Health Study. The researchers used high-resolution satellite imagery to determine the level of vegetation within 250 meters and 1,250 meters of each participant’s home. They followed the women from 2000 to 2008, tracking changes in vegetation and the 8,604 deaths that occurred.

The researchers observed different mortality rates for specific causes of death as well as a lower overall mortality rate. When comparing women in the areas with highest greenness to women in the lowest, the death rate from kidney disease was 41 percent lower, respiratory disease was 34 percent lower, and cancer deaths were 13 percent lower.

“It is important to know that trees and plants provide health benefits in our communities, as well as beauty,” said NIEHS director Linda Birnbaum, Ph.D. “The finding of reduced mortality suggests that vegetation may be important to health in a broad range of ways.”

Citation: James P, Hart JE, Banay RF, Laden F. 2016. Exposure to greenness and mortality in a nationwide prospective cohort study of women. Environmental Health Perspectives; doi:10.1289/ehp.1510363 [Online 14 Apr 2016].

(Virginia Guidry, Ph.D., is a technical writer and public information specialist in the NIEHS Office of Communications and Public Liaison and a regular contributor to the Environmental Factor.)

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