Heat has stronger effect on health in less developed cities, study finds

Compared to high income cities, less developed cities in Brazil have a higher hospitalization rate associated with increased heat exposure, according to a new study published this week in PLOS Medicine by Yuming Guo of the Monash University, Australia, and colleagues.

Heat exposure, which will increase with global warming, is associated with increases in mortality and morbidity but little is known about the socioeconomic disparities in vulnerability to heat. In the new study, researchers collected daily hospitalization and climate data in the hot season during 2000 through 2015 from 1,814 Brazilian cities covering 78.4% of the Brazilian population. 49 million hospitalizations were studied.

For cities of lower middle income, as classified by the World Bank, every 5°C increase in daily mean temperature during the hot season was associated with 5.1% (95%CI 4.4-5.7, p<0.001) increase in all-cause hospitalization. For cities of middle income, every 5°C temperature increase was associated with a 3.7% (95%CI 3.3-4.0, p<0.001) increase in hospitalization. While for cities of high income, the temperature increase was only associated with a 2.6% (95%CI 1.7-3.4, p<0.001) increase in hospitalization. The inter-city disparities in the association were strongest for children and adolescents, and the disparities were particularly evident for certain diseases including heart disease, asthma, pneumonia, renal diseases, mental health conditions and neoplasms.

"Increasing heat exposure along with global warming could be a potential driver for exacerbating inter-city health inequalities," the authors say. "More attention should be paid to less developed cities in Brazil to tackle the morbidity burden of heat exposure, in order to promote health equity under a global warming trend."