Independent and combined effect of sitting time and physical activity on all-cause mortality in Spain: a population-based prospective study

The extent to which physical activity (PA) may offset the risks associated with sedentarism is not yet well understood. We evaluated the independent and the combined effects of PA and sitting time (ST) on all-cause mortality in the Spanish population. Prospective study with 31 100 participants aged 18-69 years from the 2011-2012 and 2017 National Health Surveys; data were linked to mortality records through December 2022. ST was categorized as ≤4 h/day, >4-6 h/day, and >6 h/day, and PA was assessed using the International Physical Activity Questionnaire. PA was classified as (i) low, moderate, or high and (ii) adherence to World Health Organization (WHO) recommendations. Relative risks (RR) were estimated using Poisson regression models. The median follow-up time was 5.7 years, recording 1128 deaths. Individuals with ST >6 h/day had an RR (95% confidence interval) of 1.60 (1.34; 1.92) compared to those with ST ≤4 h/day. In contrast, those with high vs. low PA had an RR of 0.63 (0.51; 0.79), and those meeting WHO recommendations had an RR of 0.60 (0.50; 0.73). When analyzed jointly, individuals who met recommendations and had low ST, compared to those with moderate and high ST, had estimated RRs of 1.17 (0.75; 1.85) and 1.30 (0.83; 2.05), respectively. Among those who did not meet recommendations, the RR increased to 1.51 (1.19; 1.92), 2.06 (1.59; 2.68), and 2.65 (2.06; 3.42) for low, moderate, and high ST, respectively. PA and ST are independently associated with mortality. The risk associated with sedentarism can be partially offset by being physically active.