Nighttime Cold Stress and Cardiovascular Emergency Hospitalizations: A Time-Series Analysis by Sex and Age in a...

Cold temperature can increase cardiovascular risks even in subtropical regions, where infrequent exposure and limited infrastructure may limit cold adaptation. Risks may intensify at night because of declining temperature and reduced thermoregulatory capacity during sleep, yet the impact of nighttime cold exposure remains underexplored.

A time-series ecological study using quasi-Poisson regression and distributed lag nonlinear models assessed associations between cold exposure and 417 044 emergency hospitalizations for cardiovascular diseases, including acute myocardial infarction, congestive heart failure, and cerebrovascular diseases), in Hong Kong (2012-2022). Cold days and nights were defined as periods with hourly temperature below the 5th percentile of daytime maximum or nighttime minimum. Cold intensity was quantified using cold day excess and cold night excess; models were adjusted for air pollution, relative humidity, and temporal trends.

Cold night excess was associated with stronger hospitalization risks than cold day excess across all cardiovascular outcomes, with the highest risks for congestive heart failure, followed by acute myocardial infarction and cerebrovascular diseases. Relative risks for cold night excess versus cold day excess were 1.44 (95% CI: 1.40-1.48) versus 1.19 (1.18-1.21) for congestive heart failure, 1.26 (1.22-1.30) versus 1.12 (1.10-1.30) for acute myocardial infarction, and 1.06 (1.04-1.08) versus 1.03 (1.02-1.03) for cerebrovascular disease (all P<0.01). From 2012 to 2022, 201 cold nights were linked to 6805 (6045-7536) excess cardiovascular disease hospitalizations. Relative risks increased with age, especially among those aged ≥90 years.

Public health strategies need to address not only heat but also nighttime cold stress. Targeted interventions are crucial to mitigate risks in subtropical cities.