New research from Harvard School of Public
Health (HSPH) suggests that seemingly small changes in summer temperature
swings -- as little as 1°C 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
study will be published online April 9, 2012 in the Proceedings of the National
Academy of Sciences.
"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," said
Antonella Zanobetti, senior research scientist in the Department of
Environmental Health at HSPH and lead author of the study. "This
variability can be harmful for susceptible people."
In
recent years, scientists have predicted that climate change will not only
increase overall world temperatures but will also increase summer temperature
variability, particularly in mid-latitude regions such as the mid-Atlantic
states of the U.S. and sections of countries such as France, Spain, and Italy.
These
more volatile temperature swings could pose a major public health problem, the
authors note.
Previous
studies have confirmed the association between heat waves and higher death
rates. But this new research goes a step further. Although heat waves can kill
in the short term, the authors say, even minor temperature variations caused by
climate change may also increase death rates over time among elderly people
with diabetes, heart failure, chronic lung disease, or those who have survived
a previous heart attack.
The
researchers used Medicare data from 1985 to 2006 to follow the long-term health
of 3.7 million chronically ill people over age 65 living in 135 U.S. cities.
They evaluated whether mortality among these people was related to variability
in summer temperature, allowing for other things that might influence the
comparison, such as individual risk factors, winter temperature variance, and
ozone levels. They compiled results for individual cities, then pooled the
results.
They
found that, within each city, years when the summer temperature swings were
larger had higher death rates than years with smaller swings. Each 1°C increase
in summer temperature variability increased the death rate for elderly with
chronic conditions between 2.8% and 4.0%, depending on the condition. Mortality
risk increased 4.0% for those with diabetes; 3.8% for those who'd had a previous
heart attack; 3.7% for those with chronic lung disease; and 2.8% for 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.
In
addition, the researchers found the mortality risk was 1% to 2% greater for
those living in poverty and for African Americans. The risk was 1% to 2% lower
for people living in cities with more green space.
Mortality
risk was higher in hotter regions, the researchers found. Noting that
physiological studies suggest that the elderly and those with chronic
conditions have a harder time than others adjusting to extreme heat, they say
it's likely these groups may also be less resilient than others to
bigger-than-usual temperature swings.
"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," said Joel Schwartz, professor of environmental epidemiology
at HSPH and senior author of the paper. "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."
Support
for the study was provided by the U.S. Environmental Protection Agency and the
National Institute of Environmental Health Sciences.
sciencedaily.com
No comments:
Post a Comment