Quantifying the Effects of Time Spent Sitting on Mortality
The study noted here provides an interesting addition to the debate over whether time spent sitting is harmful to health independently of its contribution to time spent being sedentary. Time spent sitting increases mortality, while time spent active or undertaking exercise decreases mortality. The results of this large epidemiological study quantify how much additional exercise is required to mitigate the mortality increase resulting from time spent sitting. The results also have the look of common sense at the end of the day; the intuition that one should compensate for a desk job with additional exercise outside work turns out to be true.
To quantify health risks associated with prolonged occupational sitting and to determine whether there is a certain threshold of physical activity that may attenuate it. This prospective cohort study included participants in a health surveillance program in Taiwan who were followed-up between 1996 and 2017. Data on occupational sitting, leisure-time physical activity (LTPA) habits, lifestyle, and metabolic parameters were collected. The all-cause and cardiovascular disease (CVD) mortality associated with 3 occupational sitting volumes (mostly sitting, alternating sitting and nonsitting, and mostly nonsitting) were analyzed applying multivariable Cox regression models to calculate the hazard ratios (HRs) for all participants and by subgroups, including 5 LTPA levels and a personal activity intelligence (PAI)-oriented metric. Deaths occurring within the initial 2 years of follow-up were excluded to prevent reverse causality.
The total cohort included 481,688 participants (mean age 39.3 years). The study recorded 26,257 deaths during a mean follow-up period of 12.85 years. After adjusting for sex, age, education, smoking, drinking, and body mass index, individuals who mostly sat at work had a 16% higher all-cause mortality risk (HR, 1.16) and a 34% increased mortality risk from CVD (HR, 1.34) compared with those who were mostly nonsitting at work. Individuals alternating sitting and nonsitting at work did not experience increased risk of all-cause mortality compared with individuals mostly nonsitting at work (HR, 1.01). For individuals mostly sitting at work and engaging in low (15-29 minutes per day) or no (under 15 minutes per day) LTPA, an increase in LTPA by 15 and 30 minutes per day, respectively, was associated with a reduction in mortality to a level similar to that of inactive individuals who mostly do not sit at work. In addition, individuals with a PAI score exceeding 100 experienced a notable reduction in the elevated mortality risk associated with prolonged occupational sitting.