Temperatures below 23°C are associated with 20 times more deaths than hotter weather, according to a study by scientists from the Icahn School of Medicine at Mount Sinai. The findings were published in the American Journal of Preventive Cardiology (AJPC).

Researchers analyzed more than 14 million cardiovascular-related deaths among people over the age of 25 across 819 U.S. counties. The dataset covered the period from 2000 to 2020 and included about 80% of the country’s population. Scientists compared mortality statistics with local temperature data to assess how deviations from the “optimal” temperature affect the risk of death.

The analysis showed that the lowest cardiovascular mortality occurs at around 23°C. When temperatures deviate from this level, the risk increases—but cold has a significantly stronger impact than heat.

According to the researchers, temperatures below 23°C are linked to approximately 40,000 deaths per year, accounting for about 6.3% of all cardiovascular deaths. In contrast, higher temperatures are associated with around 2,000 deaths annually (about 0.33%).

“In total, over two decades, this amounts to roughly 800,000 deaths related to cold weather, compared to about 40,000 linked to heat. Approximately one in 16 cardiovascular deaths is associated with cold weather, whereas the effect of heat is seen in about one in 300 cases,” the scientists calculated.

The researchers note that cold weather can increase strain on the heart in several ways. Low temperatures cause blood vessels to constrict and raise blood pressure. In addition, people are more likely to engage in sudden physical exertion during winter—such as shoveling snow—which can trigger heart attacks or strokes in individuals with underlying cardiovascular conditions.