Most epidemiological studies that have examined the detrimental effects of ambient hot and cold temperatures on human health have been conducted in high-income countries. In India, limited evidence on temperature and health risks has focused mostly on the effects of heat waves and has mostly been from small scale studies.

A goal of a study published in PLoS Medicine was to quantify heat and cold effects on mortality in India using a nationally representative study of the causes of death and daily temperature data for 2001-2013.

In this study, distributed-lag nonlinear models were applied with case-crossover models to assess the effects of heat and cold on all medical causes of death for all ages from birth, as well as on stroke, ischemic heart disease (IHD) and respiratory diseases among adults aged 30-69 years. Here, the attributable risk fractions were calculated by mortality cause for extremely cold (0.4 to 13.8°C); moderately cold (13.8°C to cause-specific minimum mortality temperatures); moderately hot (cause-specific minimum mortality temperatures to 34.2°C); and extremely hot temperatures (34.2 to 39.7°C). Furthermore, the temperature-attributable deaths were calculated using the United Nations death estimates for India in 2015.

Mortality from all medical causes, stroke and respiratory diseases showed excess risks at moderately cold temperature and hot temperature. For all examined causes, moderately cold temperature was estimated to have higher attributable risks for all medical deaths; 27.2% for stroke; 9.7% for IHD; and 6.5% [3.5 to 9.2] for respiratory diseases – than extremely cold, moderately hot and extremely hot temperatures. In the year 2015, 197,000 (121,000-259,000) deaths from stroke, IHD and respiratory diseases at ages 30-69 years were attributable to moderately cold temperature, which was 12- and 42-fold higher than totals from extremely cold and extremely hot temperature, respectively.

From the results, it was inferred that public health interventions aimed to mitigate temperature effects need to focus not only on extremely hot temperatures, but also on moderately cold temperatures. Future absolute totals of temperature-related deaths are likely to depend on the large absolute numbers of people exposed to both, extremely hot and moderately cold temperatures.

Source: PLoS Medicine. 2018 Jul 24;15(7):e1002619. doi: 10.1371/journal.pmed.1002619.