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19th June 2022
The cardiovascular (CVD) risk associated with prolonged periods of sitting is higher among for individuals from lower and lower-middle income countries compared to high-income countries. This was the conclusion of an analysis of data from the Prospective Urban Rural Epidemiology (PURE) study by Chinese researchers.
The World Health Organization guidelines on physical activity and sedentary behaviour acknowledge the effect on CVD risk of prolonged sedentary behaviour in both adults and children, noting that higher amounts of sedentary behaviour are associated with detrimental effects on all-cause mortality, cardiovascular disease mortality and cancer mortality and incidence of cardiovascular disease, type 2 diabetes and cancer. Although increased levels of physical activity are generally required to improve CVD risk among the population, a 2019 systemic review concluded that higher levels of total daily sitting time were associated with an increased risk of cardiovascular disease and diabetes, independent of physical activity. However, the evidence to date that sedentary behaviour is linked with an increased CVD risk has been largely derived from high-income countries and which therefore highlights the need to examine the generalisability of these findings to low or middle-income countries.
In the present study, the Chinese team sought to determine the association between self-reported sitting time and CVD risk in countries of varying income levels using data from PURE, a large-scale, prospective cohort study which has recruited individuals aged 35 to 70 from 21 countries across regions of Africa, Asia, Europe, the Middle East, and North and South America. Information on sitting time and total physical activity were collected using a validated questionnaire and daily sitting time was categorised into four groups: < 4 hours/day; 4 to 6 hours/day; 6 to 8 hours/day and > 8 hours/day. For the current analysis, the primary outcome of interest was an assessment of CVD risk, based on a composite of all-cause mortality and major cardiovascular events (CV mortality, non-fatal myocardial infarction, stroke or heart failure) whereas for secondary outcomes, the individual components of the composite were examined.
CVD risk and sitting time
A total of 105,677 individuals with a mean age of 50.4 years (58.6% female) were included and followed for a median of 11.1 years. At baseline the median sitting time was 4 hours but ranged from 2.6 to 7.3 hours. Overall, 13.7% of individuals came from a high income country, 47.2% from a low-middle income and 9.8% from a low income country.
During the follow-up period, there were 6233 deaths and 5696 major cardiovascular events. Using a sitting time of under 4 hours as the reference point, the fully adjusted risk of the composite outcome was highest, not surprisingly, for those sitting for > 8 hours (hazard ratio, HR = 1.19, 95% CI 1.11 – 1.28, p < 0.01) and this risk was significantly elevated above 6 hours. A similar elevated risk when sitting for > 8 hours was also seen for all-cause mortality (HR = 1.20, 95% CI 1.10 – 1.31, P < 0.01) and each of the separate components of the primary composite.
Interestingly, when researchers stratified the data by country income levels, the association between sitting time and the composite outcome was greater for individuals from low-income/low middle income countries compared to high-income/upper middle-income countries, for periods of sitting exceeding 8 hours (HR = 1.29, 95% CI 1.16 – 1.44, vs HR = 1.08, 95% CI 0.98 – 1.19, low income vs high income countries).
The authors concluded that while the data confirmed earlier studies on the adverse sequelae of prolonged sitting, this was more prominent in low-middle and low-income countries. They suggested that increased physical activity represented an important strategy to reduce CVD risk due to prolonged sitting.
Li S et al. Association of Sitting Time With Mortality and Cardiovascular Events in High-Income, Middle-Income, and Low-Income Countries JAMA Cardiol 2022.