Antihypertensive Medications and Risk of Heat-Related Illness During Heatwaves: Self-Controlled Case Series

To investigate whether antihypertensive medications modify the risk of heat-related illness during heatwaves among adults with hypertension in Japan.

We identified adults with hypertension in Tsukuba City administrative claims data between April 2014 and March 2019. Average daily temperature was derived from Japan Meteorological Agency data. We used a self-controlled case series (SCCS) design to estimate incidence rate ratios (IRRs) for heat-related illness during 5-day pre-heatwave, heatwave and 5-day post-heatwave periods compared to baseline within individuals. The main analysis was stratified by person-time prescribed antihypertensives (angiotensin-converting enzyme [ACE] inhibitors/angiotensin II receptor blockers [ARBs], calcium channel blockers [CCBs] or non-loop diuretics) and person-time not prescribed antihypertensives, with drug-temperature interaction assessed. Subgroup analyses were conducted for each antihypertensive class. All models were adjusted for age and season.

We observed a greater increase in the rate of heat-related illness during heatwaves versus baseline among person-time prescribed antihypertensives (IRR: 1.64, 95% CI: 1.53-1.75) than among person-time not prescribed antihypertensives (IRR: 1.42, 95% CI: 1.27-1.58), with evidence of drug-temperature interaction (p < 0.01). When examining individual drug classes, ACE inhibitors/ARBs and CCBs were associated with an increased risk of heat-related illness during heatwaves, whereas there was no evidence of an effect with diuretics.

Our findings indicate that people taking antihypertensives are more vulnerable to heat-related illnesses during heatwaves. More research is required to explore whether this is a causal effect of the medication or due to differences between those who are treated and untreated with antihypertensives that are related to the outcome.