Myocardial Infarction More Likely to Occur in Colder Weather

Another reason to hate the cold weather: in a new prospective study, lower air temperatures were associated with an increased risk of myocardial infarction (MI). 

Researchers collected daily weather data for all MIs reported to the Swedish nationwide coronary care unit registry, Swedish Web-System for Enhancement and Development of Evidence-Based Care in Heart Disease Evaluated According to Recommended Therapies (SWEDEHEART), between 1998 and 2013. This data was combined with MI date of symptom onset and coronary care unit. The final analysis included 274,029 patients (mean age, 71.7 years). 

Researchers took into account the nationwide daily mean air temperature, minimum air temperature, maximum air temperature, wind velocity, sunshine duration, atmospheric air pressure, air humidity, snow precipitation, rain precipitation, and change in air temperature. 

Myocardial infarction was more likely to occur in the presence of lower air temperature, lower atmospheric air pressure, higher wind velocity, and shorter sunshine duration, with the strongest association observed for air temperature. MI incidence was greatest on days when temperatures were < 0°C, and risk started to decline when temperatures were > 3°C to 4°C. A 1-SD increase in air temperature (7.4°C) decreased MI risk by 2.8% (unadjusted incidence ratio, 0.972; 95% CI, 0.967-0.977; P <.001). 

Study author Dr. David Erlinge told CNN by email, “When minimum temperature decreases from +20° to 0° (68°F to 32°F) the risk of suffering a heart attack increased by 14%.” 

One possible correlation researchers pointed out is that the risk of other conditions associated with increased MI risk, such as respiratory tract infections and influenza, also increases in the colder weather. 

“Season-dependent behavioral patterns, such as reduced physical activity, dietary changes, and depression, may also contribute to the increased occurrence of MI during cold weather. Vitamin D has been proposed to play an important role in the seasonality of cardiovascular disease and mortality, and this could explain the associated risk of MI and sunshine duration,” the authors wrote, adding, “However, randomized studies have failed to show any effect of vitamin D supplementation on MI risk.” 

Sources: JAMA CardiologyCNN