A case-crossover study in Canada found that 7.87 in. (20 cm) of snowfall was associated with a 16 percent higher risk of hospital admission and a 34 percent higher risk of death due to MI the following day among men compared to snowless days.
Women had a 1 percent increased risk of hospital admission and a 4 percent increased risk of death due to MI. The increased risks occurred regardless of age, cardiovascular comorbidity or cardiovascular risk factors.
Lead researcher Nathalie Auger, MD, MSc, of the University of Montreal Hospital Research Center in Montreal, and colleagues published their results online in the Canadian Medical Association Journal on Feb. 13.
“We suspect that shoveling was the main mechanism linking snowfall with MI,” Auger said in a news release. “Men are potentially more likely than women to shovel, particularly after heavy snowfalls. Snow shoveling is a demanding cardiovascular exercise requiring more than 75 percent of the maximum heart rate, particularly with heavy loads.”
The researchers evaluated 128,073 hospital admissions and 68,155 deaths due to MI in Quebec from 1981 to 2014 using two databases. They restricted the analysis to the months of November through April because there is not much snowfall during the other months. They also obtained daily snowfalls and temperatures during that time period.
Approximately 60 percent of the participants were men, and approximately 4 percent of hospital admissions and deaths due to MI occurred when there was 3.94 in. (10 cm) or more of snow. Approximately 22 percent of hospital admissions and deaths due to MI occurred when snow fell six hours or longer.
The researchers found that 24 hours of snowfall was associated with an 8 percent increased risk of hospital admissions and a 12 percent increased risk for death the following day among men compared with no snow. However, there was no association with 24 hours of snowfall and hospital admission among women. They added that similar results were found for snowfall the day of MI, but there was no association between snowfall and MI two or three days later.
The associations with snowfalls were present regardless of the presence of cardiovascular morbidity or risk factors, according to the researchers. They mentioned that participants without comorbidity or risk factors had an increased risk of hospital admission with longer durations of snowfall.
Among men, one day of 1.97 inc (5 cm) or more of snowfall was associated with a 6 percent increased risk of hospital admission due to MI, while two to three consecutive days of 5 cm or more of snowfall was associated with a 9 percent increased risk of hospital admission due to MI. In addition, among men, one day of 1.97 inc (5 cm) or more of snowfall was associated with a 14 percent increased risk of death due to MI, while two to three consecutive days of 1.97 inc (5 cm) or more of snowfall was associated with a 20 percent increased risk of death due to MI.
“These results call for caution after snowfalls, particularly for men who may be at higher risk, and may have increasing relevance over time, considering climate change and pre- dictions that extreme weather will increase,” the researchers wrote.
The researchers mentioned a few limitations of the study, including that they could have misclassified MI events because they used administrative data. They also noted that the diagnostic criteria for MI and the sensitivity of biochemical assays for MU detection changed during the study period. In addition, they had no information of sex-specific shoveling habits, the size of areas shoveled or whether participants used snow blowers or shoveled the snow themselves. Further, they wrote that the results might not be generalizable to other areas with different snowfall levels.
“Both the quantity and duration of snowfall were associated with subsequent risk of hospital admission or death due to MI in the province of Quebec, particularly among men,” the researchers wrote. “These finings are most likely related to the increased cardiac demands of snow shoveling. Climate change and the predicted increase in the frequency and intensity of winter storms raise the possibility of a greater incidence of MI in the future. Clinicians and public health practitioners should consider awareness campaigns before the winter season to inform individuals of the risk of MI after a snowfall, and possibly advise against shoveling for the most at risk patients.”