Study reports that a 1°C increase in summer mean temperature is correlated to a 2.5% increase in death rate for seniors in the southeast U.S. while a 1°C increase in winter mean temperature is associated with a 1.5% decrease.
With summer now in full swing, the hot weather prompts many people to seek relief from the sun under the shade, with a cold drink, or in the comfort of air conditioning. Hot summer temperatures can threaten the health of many people, particularly vulnerable populations like those over the age of 65. While there have been numerous studies on the impact of acute (a few days) hot weather on mortality, the impact of long-term temperatures is unknown. A group of researchers from Harvard University recently studied and reported their findings on the chronic effects of mean seasonal temperatures and within-season variability on the annual mortality of seniors residing in the southern U.S.
The health of 13 million elderly Americans (65+ years old, Medicare cohort) was examined along with ambient air temperature data from weather stations for the Southeastern U.S. during the period between the year 2000 and 2013. This climate region was of interest to the researchers as many older Americans choose to reside in states like Florida during their retirement, with the belief that a warmer climate will be more beneficial to their health compared to colder climes. The temperature variability, or standard deviation from seasonal daily temperatures in the summer months (June, July, August) and winter months (December, January February), was also assessed. Annual mortality rates were gathered for each ZIP code and compared to temperature data.
The results showed that a 1°C rise in summer mean temperature was correlated with a 2.5% increase in death rate for seniors in the southeast U.S. The death rate was higher in years and in areas with high summer temperatures and the researchers suggest that this indicates little acclimatization of seniors to hot weather. In contrast, a 1°C rise in winter mean temperature in this region was correlated with a 1.5% decrease in death rate. Therefore, living in an area with a warmer summer mean temperature had adverse health effects.
Variations in daily temperatures from the average during the summer and winter season, manifested as heat waves or cold waves, were harmful to health overall. A 1°C rise in temperature variability during summer or winter was correlated with a 3.7% and 0.6% increase in death rate, respectively. These results suggest that there is a higher risk for mortality in years with variable weather compared to the overall 14-year study mean temperature.
Location and demographic data revealed that seniors residing in low population density areas or poor areas were more sensitive to seasonal mean temperature changes compared to those in the city. This may be due to a lack of health care access or being unable to afford air conditioning and heating. In addition, the older cohort of seniors aged 75 and up was particularly sensitive to seasonal mean temperature changes and this was reflected in mortality data.
The study concludes that chronic hot temperatures and increased temperature variability of the southern U.S. were correlated with increased mortality in seniors. Interestingly, the high prevalence of air conditioning in this region didn’t seem to reduce mortality rates. The results presented in this work are very timely, as climate change is slowly increasing global temperatures – last year was America’s warmest on record according to The Third National Climate Assessment. Thus, this and future studies will allow researchers to better understand the link between air temperature and human health in different climate zones, and in turn reduce resulting adverse health effects to vulnerable populations.
Written By: Fiona Wong, PhD