Fall, winter weather linked to increased risk of MI

Colder temperatures, stronger winds and fewer hours of sunlight could all raise a person’s risk of myocardial infarction, researchers reported this week in JAMA Cardiology.

Corresponding author David Erlinge, MD, PhD, of Lund University in Sweden, and coauthors said a tenuous connection between weather and adverse cardiovascular events has existed for nearly a century, stemming back to a 1926 report that concluded more cases of coronary thrombosis occurred in New England during the winter.

“In the last decades, evidence linking the incidence of MI to colder temperatures and snow has been published,” Erlinge et al. wrote in the journal. “However, most studies have used surrogate variables, such as the International Statistical Classification of Diseases, Tenth Revision codes, as indicators of MI, and many studies have only looked at air temperature and snow. Other meteorological parameters have not been as widely investigated.”

To add to the existing body of research, Erlinge and his colleagues launched an observational study of the SWEDEHEART database, a collection of information from heart patients in Sweden. They considered data from 1998 to 2013, which spanned 274,029 consecutive MI patients treated at Swedish hospitals. Around a third of patients presented with ST-segment elevation MI (STEMI).

The researchers merged patient information with daily weather data from the Swedish Meteorological and Hydrological Institute, taking into account factors like average daily air temperatures, wind velocity, sunshine duration, snow, rain, humidity and air pressure. 

Erlinge and coauthors found, in their pool of patients who were on average in their early 70s, incidence of MI increased with lower air temperature, lower atmospheric air pressure, higher wind velocity and shorter sunshine duration. Temperature proved the strongest link—each standard deviation increase of 7.4 degrees Celsius resulted in a 2.8 percent reduced risk of MI.

MI was most common on days when the air temperature sank lower than 0 degrees Celsius, and risk seemed to decline when it rose to about 3 or 4 degrees Celsius. Results were consistent across subgroups and healthcare regions, including a pronounced positive association of MI with snow and wind in the northernmost regions of the country.

“A number of physiologic mechanisms have been proposed to explain the association of cold weather and MI, among which coronary vasoconstriction is the most probable cause,” Erlinge et al. wrote. “Cold as a pressor for coronary vasoconstriction was proposed as early as the 1970s, and whereas cold did not alter coronary vascular resistance in healthy individuals, it was significantly altered in patients with coronary heart disease.”

Other conditions associated with cold weather, including the flu and respiratory tract infections, also raise the average person’s risk of MI, the authors said, which could partly explain their results. Season-dependent behavioral patterns, like reduced activity, depression and dietary changes, could also contribute.

“In this large, nationwide study, low air temperature, low atmospheric air pressure, high wind velocity and shorter sunshine duration were associated with risk of MI, with the most evidence association observed for air temperature,” Erlinge and colleagues said. “This study adds to knowledge on the role of weather as a potential trigger of myocardial infarction.”