The impact of high temperatures and heatwaves on health outcomes among working-age adults (15–64 years): a systematic review and meta-analysis

Background

High temperature is a well-documented public health threat affecting people of all age groups. While occupational studies have assessed heat impacts on workers, the broader health effects on the working-age population remain underexplored. This study systematically reviewed and quantified the health effects of high temperatures and heatwaves among working-age adults.

Method

Systematic searches were conducted in PubMed, Scopus, and Embase for peer-reviewed epidemiological studies published up to January 2025. Eligible studies examined the effects of high temperatures and heatwaves on all-cause and cause-specific morbidity and mortality in individuals aged 15–64 years. A random-effects meta-analysis was performed to pool relative risks (RRs) per 1°C increase in temperature and across heatwave intensities. The study protocol was registered with PROSPERO (CRD42024528637).

Findings

Of 4,755 identified studies, 165 met the inclusion criteria, with 138 eligible for meta-analysis. A 1°C increase in heat exposure was associated with a 2.3% increase in morbidity (RR 1.023 [95% CI 1.019–1.027], I2 = 99.7%) and a 1.6% increase in mortality (RR 1.016 [95% CI 1.013–1.018], I2 = 78.9%) among working-age adults. The risk of morbidity and mortality associated with rising temperatures was greater in lower-income countries. Heatwaves also significantly affected health among working-age adults, with a 5.3% increase in morbidity (RR 1.053 [95% CI 1.042–1.064], I2 = 90.7%) and a 3.8% increase in mortality (RR 1.038 [95% CI 1.020–1.057], I2 = 57.7%). The greatest risk of morbidity was observed during middle-intensity heatwaves, while the highest risk of mortality was found during high-intensity heatwaves. The risk of morbidity from heat-related illnesses and genitourinary disorders showed the strongest associations with rising temperatures and heatwaves.

Interpretation

High temperatures and heatwaves significantly increase morbidity and mortality among working-age adults (15–64 years), particularly due to occupational and environmental factors. Greater risks were observed in humid subtropical and Mediterranean climates, with notable increases in heat-related illnesses and genitourinary disorders. These findings highlight the need for broader heat vulnerability assessments and inclusive prevention strategies beyond workplace settings.