Large analyses with more than one million participants show that sufficient physical activity almost completely neutralizes the mortality risk of prolonged sitting. The risk lies in the combination of sitting a lot and moving little, not in sitting itself. Increasing total physical activity volume is the most important measure, not reducing sitting time.
Sitting a lot is a real concern, but the good news is right there in the data: people who exercise enough almost completely neutralise the risk of prolonged sitting. In the largest analyses, involving more than one million participants, the most active people who also sat for more than eight hours a day had barely any higher risk of death than people who sit little. The problem, then, is not sitting itself, but the combination of a lot of sitting and very little movement.
The most direct lever is therefore to increase your total volume of physical activity, not necessarily to reduce your sitting time. The threshold at which risk starts to rise is around six to eight hours of sitting per day, but that figure is based on self-reporting, and people generally underestimate how much they sit, so in practice you are probably sitting more than you think. Getting up regularly or taking a walking break can help bring that actual sitting time down, but it is the movement that carries the most weight.
What that volume of physical activity specifically needs to be cannot be pinned down precisely on the basis of these records, but the studies show that the effect is already visible at levels that most people should find achievable, and that more consistently delivers more benefit. If you want to know objectively whether you are moving and sitting enough, wearables or activity trackers are considerably more accurate than your own estimate, although that data too is not without measurement noise.
Strong evidence, based on 4 source(s), including controlled or causal research.