S u m m a r y :
Cold air temperatures might be an external trigger for heart attacks, suggests a new study presented today, August 30, at European Society of Cardiology Congress.
“Nothing burns like the cold”. Apparently, (one of the characters of) George R.R. Martin was right. Cold air temperatures might be freezing hearts—according to the new study, winter might be associated with an increasing trend of heart attacks: the daily average number of such cases are significantly higher during colder days than when it is warmer. The findings encompass data collected over a period of 16 years, entailing over 280,000 patients.
Fewer Heart Attacks in Summer
The incidence of heart attacks declines in summer and peaks during winter, constituting a seasonal variation in their occurrence, explains study first author Dr Momam A. Mohammad from Lund University, Skane University Hospital, Lund, Sweden. The cause behind this link remains unclear though; it might be anything associated with winter, from the colder temperatures to the behavioural changes.
Mohammad and his team, led by Prof David Erlinge, aimed at understanding the connections between heart attack occurrence and weather conditions, the latter including variables like air temperature, sunshine duration, precipitation, and air pressure.
The Heart Does Not Like the Cold
Mohammad and his colleagues studied data from the Swedish myocardial infarction registry (SWEDEHEART) that documented heart attacks treated from January 1998 to December 2013. Together with this, the specific weather conditions during which the heart attacks happened were recorded from the Swedish Meteorological and Hydrological Institute (SMHI).
The findings show that the average number of heart attacks per day was much greater when the temperatures were colder. This link was seen throughout the different healthcare regions from which the data was collected. According to the researchers, this meant that 4 more heart attacks would happen daily in Sweden when the average daily temperature was under 0 °C than when it was over 10 °C. Another correlation entails other weather aspects: heart attacks would be more frequent during days of higher wind velocities, limited sunshine duration, and higher air humidity. Again, this association was found to be consistent throughout the different subgroups.
“Our results consistently showed a higher occurrence of heart attacks in sub-zero temperatures. The findings were the same across a large range of patient subgroups, and at national as well as regional levels, suggesting that air temperature is a trigger for heart attack,” says Dr Mohammad.
If You’re Healthy, Does the Cold Bother Your Heart?
One of the explanations of the link between heart attacks and cold temperatures is that cold causes the constriction of surface blood vessels resulting in decreased heat conducted throughout the skin. This, then, increases blood pressure in arteries, heart rate, and responses like shivering might also be generated. All of this increase metabolism, in turn increasing body temperature. While these are normal mechanisms, people with blocked coronary arteries know a different story: the reactions might lead to heart attacks in their cases, says Dr Mohammad.
However, he does add that other factors might have also been at play.
“Respiratory tract infections and influenza are known risk factors for heart attack that have a clear seasonal variation. In addition, seasonal-dependent behaviours such as reduced physical activity and dietary changes could play a role in the increased occurrence of heart attack during colder weather.”