Background: Cold temperatures are associated with increased risk for cardiovascular and respiratory disease mortality. Due to limited temperature regulation in prisons, incarcerated populations may be particularly vulnerable to cold-related mortality.

Methods: We analyzed mortality data in US prisons from 2001 to 2019. Using a case-crossover approach, we estimated the association of a 10 °F decrease in cold temperature and extreme cold (days below the 10th percentile) with the risk of total mortality and deaths from heart disease, respiratory disease, and suicide. We assessed effect modification by personal, facility, and regional characteristics.

Results: There were 18,578 deaths during cold months. The majority were male (96%) and housed in a state-operated prison (96%). We found a delayed association with mortality peaking 3 days after and remaining positive until 6 days after cold exposure. A 10 °F decrease in temperature averaged over 6 days was associated with a 5.1% (95% confidence interval [CI]: 2.1%, 8.0%) increase in total mortality. The 10-day cumulative effect of an extreme cold day was associated with an 11% (95% CI: 2.2%, 20%) increase in total mortality and a 55% (95% CI: 11%, 114%) increase in suicides. We found the greatest increase in total mortality for prisons built before 1980, located in the South or West, and operating as a dedicated medical facility.

Conclusions: Cold temperatures were associated with an increased risk of mortality in prisons, with marked increases in suicides. This study contributes to the growing evidence that the physical environment of prisons affects the health of the incarcerated population.