Don’t sit for too long at a time — get up and move every now and then

Cost: It costs nothing; getting up a few times doesn’t take much time at all. The hard part is that once you sit down, you tend to lose track of time, so you need a reminder.
In plain terms: People who sit the longest have a 2.6 times higher chance of dying during the same period compared to those who sit the least. Sitting continuously for long stretches adds extra risk on top of that. However, if you get 60–75 minutes of moderate-intensity activity each day, this extra risk from prolonged sitting is largely offset.
Benefit: One U.S. observational study used accelerometers to measure activity levels without grouping participants. It divided people into four groups based on their total daily sitting time. Those in the group with the most daily sitting time had a 2.63 times higher risk of death than those in the group with the least (HR 2.63). The study also split participants into four groups based on the longest continuous sitting period; those in the group with the longest continuous sitting time had a 1.96 times higher risk than those in the group with the shortest continuous sitting time (HR 1.96). This shows that both total daily sitting time and the length of each continuous sitting period are independently linked to mortality risk. Another meta-analysis of millions of participants also used observational data without grouping. It found that people who sat for over 8 hours a day and did little to no exercise had a 1.59 times higher risk of death compared to those who sat for less than 4 hours a day and were the most active. For the most active group, even if they sat for over 8 hours a day, their risk ratio was only 1.04 — no statistically significant difference was observed.
Evidence grade: A
Sources:Diaz KM 等 (2017). Patterns of Sedentary Behavior and Mortality in U.S. Middle-Aged and Older Adults: A National Cohort Study. Annals of Internal Medicine. https://doi.org/10.7326/M17-0212；Ekelund U 等 (2016). Does physical activity attenuate, or even eliminate, the detrimental association of sitting time with mortality? A harmonised meta-analysis of data from more than 1 million men and women. Lancet. https://doi.org/10.1016/S0140-6736(16)30370-1
Notes: The reliable conclusion here is that how much you move matters more than how long you sit; when you get enough exercise, the extra risk from prolonged sitting largely disappears. It’s worth noting that these studies are purely observational, so many of the people who sit the most already have underlying health issues — the “2.63 times higher risk” partly reflects this pre-existing health condition. Additionally, the same meta-analysis found that watching TV for over 3 hours a day increases risk across all activity levels; for the most active group, this risk threshold only rises to 5 hours a day.