Setareh Salehi Omran, MD
Leisure sedentary time is increasing in the western world, particularly among young adults. While the association between physical activity and lower risk of stroke is well-known, data is limited on the association between sedentary time and stroke. It is also unclear whether an association between sedentary time and stroke can be modified with higher levels of physical activity.
Joundi et al. used a large cohort of healthy individuals from the nationwide Canadian Community Health Survey (CCHS) with linked administrative records to determine whether excess leisure sedentary time was associated with elevated long-term risk of stroke. The CCHS represents 97% of the Canadian household population and collects health-related information, including self-reported sedentary time and baseline covariates. The authors used nine cycles of the CCHS to identify healthy individuals >40 years of age without prior stroke, heart disease, or cancer history. Information was only available on sedentary time that was spent for leisure (not school- or work-related) and was categorized as <4 hours, 4 to <6 hours, 6 to <8 hours, and ≥8 hours/day.
The authors also measured weekly leisure-time physical activity by calculating the frequency and duration of each type of physical activity, as well as the metabolic equivalent value of the activity. The majority of the CCHS population is linked to administrative records, where hospitalizations and emergency department visits can be followed. All patients were followed for a minimum of 5 years. The primary outcome was acute stroke during follow-up or until December 31, 2017. Cox proportional regression models were used to obtain the risk of stroke by category of leisure sedentary time while assessing for modification by physical activity, age, and sex, and adjusting for demographics and vascular risk factors.
A total of 143,180 participants were included. The majority (67%) of participants were <60 years of age, and mean leisure sedentary time was 4.08 hours. There were a total of 2965 stroke events during a median follow-up of 9.4 years. The authors found a three-way interaction between leisure sedentary time, physical activity, and age. The risk of stroke with excess leisure sedentary time ≥8 hours was elevated in individuals <60 years of age with low physical activity. This association was still present after adjusting for demographics and vascular risk factors (fully adjusted hazard ratio 4.50, 95% CI 1.64-12.3), as well as in sensitivity analyses adjusting for mood disorders and competing risk of death. There was no significant association between any sedentary time category and risk of stroke among individuals >60 years of age.
The study has several noteworthy limitations, including lack of data on occupational sedentary time, inability to account for mobile device use, and reliance on self-reported measurements of sedentary time. The results add to the urgency of public health efforts of increasing physical activity and minimizing sedentary time as a way of decreasing the risk of cardiovascular events in young adults.