Passively sitting supported by “ergonomic” chairs has been associated with a host of health problems: poor posture, weakened core, metabolic syndrome, and even some forms of cancer. It’s a worrisome list, and taken altogether makes a strong case for sitting less, or at least sitting differently.
But a recent paper in the prestigious medical journal JAMA1 ups the ante, adding still another condition to the list of sitting associated diseases. Researchers in the UK studied almost 50,000 older adults, and found that those who sat the most had a much greater risk of dementia. Although the association of dementia with passive sitting was non-linear, those who sat the most the risk of dementia was three times higher than the group that spent the least time sitting.
Discouragingly, this study found that exercising did nothing to reduce the risk of dementia. As the noted professor of biological sciences and anthropology at the University of Southern California David Raichlen observed in a recently published Washington Post article, “It looks like you can’t exercise your way out of the risk.”2 In fact, sitting seems to actually undermine exercise: people who work out but then sit for the rest of the day wind up erasing some of the expected metabolic benefits of their exertions. It seems unjust that the sitting that your job requires robs you of the benefits of the work you put in at the gym, but biology isn’t always fair.
It also turns out that occasionally getting up from your desk for a stroll or some squats doesn’t reduce the risk of dementia. Such brief “movement snacks” help lessen many of the adverse effects of sitting, but it seems that dementia is uniquely problematic. Because the risk of dementia seems to be increased by the number of hours spent sitting, the only protection is reducing the amount we sit. Or, perhaps changing how we sit. More on this below.
This most recent report in JAMA isn’t the first to note a relationship between sedentary time and dementia. A review article published in 20203 combined 18 previous studies in a single meta-analysis that included over 250,000 subjects. The authors concluded increased sedentary time was associated with an increase in dementia, and further, that this effect was not small: on average a 27% higher rate of dementia.
The authors of the JAMA paper note that their finding accords with this previous research. So, altogether the case for correlation between sitting and dementia seems strong.
But correlation does not prove causation. Indeed, it might be that impending dementia makes people more likely to stay seated, perhaps because they are afraid of falling or getting lost. In this case dementia would “cause” sitting, rather than the more obvious link that sitting causes dementia. The authors are aware of this problem, and were careful to establish the sitting pattern of subjects four years before they were allowed into the study. This simple maneuver allowed the authors to exclude patients who were about to develop dementia from the dataset. It’s a standard correction, but, as the authors admit, “reverse causality cannot be fully ruled out.”
It’s possible to sort out the problem of reverse causality experimentally, but this would require a randomized trial in which subjects were randomly assigned to sit for more or fewer hours each day. Unfortunately, such an experiment cannot be performed, because we already have very strong evidence that prolonged sitting is a health risk; thus, it would not be ethical to assign subjects to sit more given the known risks.
Would sitting differently help? We don’t know that active sitting decreases the risk of dementia compared to passive sitting, but because the biochemistry induced by active sitting is closer to walking than sitting it might well be that active sitting provides some protection. Riddling this out will take a well-designed study and several years and massive funding to complete, so we’re unlikely to have an answer soon.
But, in the meantime, it seems wise to sit less, and to sit actively whenever possible. Because, while dementia has a host of contributing factors, dialing down any of them helps protect against this devastating condition. And because dementia is so common in the USA (3% of 70-year-olds, rising to 33% of 90-year-olds)4 the stakes couldn’t be higher.
It turns out that there’s also a “to do list” for avoiding dementia, a list that thankfully is pretty short: According to the Alzheimer’s Society one need only stay physically active, eat healthy, avoid smoking, and stay mentally and socially active.5 It’s a shockingly non-technical list, stuff your grandmother would have recommended. But note that “stay physically active” is placed first on this well thought out list, likely because it’s the most important.