Physiological responses to heat exposure in a general population cohort in Denmark: the Lolland-Falster Health Study.

Background: Rising global temperatures due to climate change pose a health risk. Mortality and morbidity increase during heat events affects various organ systems. While warmer countries face higher risks, even colder regions show elevated mortality during hot periods. This study examines physiological responses to heat exposure using data from the general Danish population cohort Lolland-Falster Health Study (LOFUS) during the summers of 2016-2019.

Methods: In this cross-sectional study, we analysed health data from 3804 individuals aged ≥15 years. Data were analysed across organ systems: cardiovascular system, lung function, renal system, inflammation, coagulation, and liver function. Meteorological data from the Danish Meteorological Institute provided information on temperature and humidity. Heat exposure was defined as one day ≥28°C heat index the day prior to examination. Adjusted multiple linear regression was applied to analyse differences between the two groups.

Results: There were 46 of 368 days with temperatures ≥28°C heat index. In total, 396 participants were heat-exposed (exposure group), while 3408 constituted the unexposed group. Heat exposure was associated with lower systolic blood pressure (-3.82 mm Hg [-5.72; -1.93]), higher heart rate (1.71 beats/min [0.45; 2.98]), lower oxygen saturation (-0.28% [-0.45; -0.10]), higher sodium (0.56 mmol/l [0.33; 0.79]), and higher urine albumin (0.14 mg/l [0.02; 0.27]). No significant differences were observed in inflammation, coagulation, or liver function.

Conclusion: This study reveals early physiological responses to heat with one day of heat exposure ≥28°C, particularly in the cardiovascular, pulmonary, and renal systems. These findings underline the need for tailored strategies to mitigate health risks associated with rising temperatures.