New research suggests that shoveling snow increases the risk of myocardial infection among men.
Snow shoveling is a particularly strenuous activity, and our cardiovascular system "knows" it, too.
The intense aerobic activity may be good exercise, but lifting too much heavy snow puts a disproportionate amount of strain on our arms compared with our legs, therefore increasing our heart rate, blood pressure, and oxygen demand. Together with the inhalation of cold air, this can lead to adverse cardiovascular events, also known as the "snow-shoveler's infarction."
A new study, published in the Canadian Medical Association Journal, examines the link between large snowfalls, long periods of snow, and the risk of myocardial infarction (MI).
Researchers led by Dr. Nathalie Auger, of the University of Montreal Hospital Research Centre in Montréal, Quebec, examined data from two databases, gathering a total of 128,073 patient admissions and 68,155 MI-induced deaths that occurred in Quebec between 1981 and 2014.
They analyzed the data only in areas prone to heavy snowfalls, and they collected information during the winter months between November and April. Furthermore, the researchers received detailed weather information from Environment Canada for each of the regions studied, such as daily snowfall and temperature.
Studying the link between snowfall and the risk of heart attack
Overall, Dr. Auger and team found an association between heavy snowfall and a higher risk of both nonfatal and fatal MI.
Specifically, heavy snowfall - defined as approximately 20 centimeters - correlated with a 16 percent relative increase in the chances of being admitted to the hospital due to an MI. Heavy snow was also associated with a 34 percent relative increase in the odds of dying from an MI in men.
Approximately 60 percent of al MI-related hospital admissions and deaths were in men, but no adverse cardiovascular effects were noticed in women.
The study also found that the probability of fatal MI increased proportionally with the consecutive number of snow days. The likelihood rose particularly in the day most close to the snowfall period, with a third of the MIs in men occurring the day following a snowfall. This association was even stronger for longer-lasting snowfalls - 2 to 3 days, for example.
As Dr. David Alter points out in an accompanying commentary to the study, this makes the possibility of causality between snow shoveling and MI very plausible.
Researchers adjusted for age, cardiovascular risk factors, and other health conditions. The risks remained high independent of these variables. However, the authors suggest that men over 50 who are at risk of cardiovascular disease or lead a sedentary lifestyle may have the highest risk of MI if they shovel large amounts of snow.
Despite study limitations, snow shoveling still a plausible cause
Lastly, the authors also point out some limitations to their observational study. There is no data on gender-specific snow-shoveling habits, or other behaviors that may have taken place immediately before the snowfall. Researchers were also unaware of how the snow removal was done - manually or with the help of a snow blower, for instance.
Furthermore, in his review, Dr. Alter points out that if snow shoveling was indeed accountable for the adverse health effects, the risks of comorbidities, frailty, and MI should have risen along with the risk of cardiovascular events.
Despite these "important considerations, the hypothesis that shoveling is associated with an increased risk of MI events among men remains plausible," the authors write.
"We suspect that shoveling was the main mechanism linking snowfall with MI. Men are potentially more likely than women to shovel, particularly after heavy snowfalls. Snow shoveling is a demanding cardiovascular exercise requiring more than 75% of the maximum heart rate, particularly with heavy loads."
Dr. Nathalie Auger
In fact, Dr. Auger and colleagues advise public officials to come up with awareness campaigns that dissuade people from this activity, especially if their health is already poor.