You may have seen the recent article in New York Magazine called Sitting is Bad for You. So I Stopped. For a Whole Month. I understand that humor is part of the intention of this article, but its very premise – that sitting is indeed bad for you – is now widely accepted by lay people (there are people in my office now who have redesigned their workspaces so they can stand while working) and I kind of wonder why.
Usually this sort of health hokum is based on a cohort study, with weak findings, that are misinterpreted as causal.
But let’s look for ourselves. This Time articles from 2012 cites a large cohort study. The cohort study finds an increase in time spent sitting and all cause mortality (so for instance those who self-report a lot of sitting are more likely to be murdered, or commit suicide, or die in a car accident). But not much more likely. The associations are quite weak. Those (above age 45) who sit up to 11 hours per day are only 15% more likely to die in 3 year period than those who sit practically not at all – less than 4 hours a day.* But that didn’t stop the report’s authors from making statements like this:
That morning walk or trip to the gym is still necessary, but it’s also important to avoid prolonged sitting. Our results suggest the time people spend sitting at home, work and in traffic should be reduced by standing or walking more.
* How does one sit less than four hours a day? How is that even possible?
That’s a very small gap, 15%. It is so small that it ought not be trusted one bit.
Very small effects (weak findings) tend to disappear or invert if you look at the data more closely. Here are some examples from this very study where the data suggests that more sitting lowers mortality:
- Age 55-64: lower mortality among those who sit 8-11 hours/day than those who sit 4-8 hours
- Ages 75+: lower mortality among those who sit 4-8 hours per day than those who sit <4 hours per day
- Participants with cardiovascular disease or diabetes: lower mortality among the 4-8 hours group than among the <4 hours group
- Overweight participants: lower mortality among the 4-8 hours group than among the <4 hours group
- Among those with higher levels of physical activity: lower mortality among the 4-8 hours group than among the <4 hours group
Were the premise correct, none of these should be the case, right?
Now, those who sit A LOT (11+ hours a day) do have significantly higher mortality rates, but we ought to wonder about them, being at one extreme end of the spectrum. We might reasonably wonder if they have other problems that cause them to both sit around a lot and to die.
That’s one hypothesis. This data set suggests all manner of hypotheses to be rigorously explored. But as evidence to support a forgone conclusion – that sitting harms health – it is unconvincing in the extreme.
So relax. Take a load off.