New research suggests that colder months are associated with a substantial rise in deaths from heart attacks, strokes, and coronary artery disease, while heat also raises risk, but to a much lesser extent. Published in the American Journal of Preventive Cardiology, the study offers one of the most extensive looks yet at how temperature affects cardiovascular mortality across the United States.

Researchers analyzed monthly temperature data and cardiovascular death rates from 819 U.S. locations, covering about 80 percent of Americans older than 25 between 2000 and 2020. They identified 23°C, or about 74°F, as the temperature linked to the lowest cardiovascular death rate. As temperatures moved above or below that point, deaths increased, forming a lopsided U-shaped pattern. The cold side of that curve was far steeper than the hot side.

Cold temperatures were associated with about 40,000 additional cardiovascular deaths per year during the study period, or roughly 6.3 percent of all such deaths. By comparison, hot temperatures contributed about 2,000 extra deaths annually, or 0.33 percent. Over two decades, that adds up to an estimated 800,000 deaths linked to cold, compared with about 40,000 tied to heat.

The study also reinforces the biological danger of cold exposure. Lower temperatures can trigger inflammation and narrow blood vessels, making it harder for the heart to function and increasing the chance of a serious event. Older adults, and people with chronic conditions such as diabetes, heart failure, and chronic kidney disease, are especially vulnerable.

The researchers argue that public health planning should pay more attention to cold-weather risk, not just heat. Hospitals and emergency services may need to prepare for more demand during colder periods, and climate-health strategies should include cold-related protections alongside heat mitigation.