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Arthur T Knackerbracket has processed the following story [arstechnica.com]:

Standing desks—and even biking desks [arstechnica.com]—are a response to a growing body of studies showing that a sedentary lifestyle creates many health risks. Regular physical activity appears to confer a degree of protection from various problems, both physical and mental, and many results indicate that this doesn't have to be Olympic-level training. Simply walking around the apartment a few times a day appears to help.

Now, a team of researchers has looked at the opposite question: Are all forms of inactivity equal? The answer is probably not. While the details depend on the health issues involved, there's likely to be some good news for people reading this, in that computer use appears to be somewhat protective against dementia.

The physical risks associated with inactivity are generally associated with lower cardiovascular health, either directly or via obesity. Even a small amount of physical activity appears capable of limiting these impacts, although increased exercise generally seems to be even better (details vary depending on the study and the exact risk being examined).

But exercise also seems to improve mental health. It can be an effective therapy for depression and other disorders, and appears to help stave off some of the unfortunate impacts of aging. "Exercise and physical activity have shown promise in reducing rates of cognitive decline, structural brain atrophy, and dementia risk in older adults," the authors write, citing the work done in other studies.

One of the oddities of some of the studies noted in the new one is that several of them used hours watching the television as a stand-in for the amount of time spent inactive. While that may have been true a few decades back, we've since greatly diversified our inactivity, with computers and mobile devices offering new ways of feeling like you're doing something without the need to do anything.

So, the researchers decided to look into this in more detail and tackle some related questions. Their study design separated computer use and TV viewing, and it looked at how each influenced the onset of mental problems associated with aging. It also examined whether physical activity could influence the association between sedentary behavior and aging-associated problems.

To do so, the researchers took advantage of the UK Biobank, a large database that combines anonymized demographics and health outcomes for hundreds of thousands of UK citizens. For this work, the team excluded people under 60 years old and focused the work on about 75,000 people who had filled in detailed information about their level of activity and leisure pursuits.

Before we get into the results, a small reminder: The work focused on the influence of sedentary behavior on mental issues. Physical health issues weren't examined—it's possible for something that looks relatively good in this analysis to be an overall negative once physical issues are factored in.

That out of the way, what did they see? With age and gender controlled for, time spent watching TV was associated with an increased risk of dementia (a hazard ratio [wikipedia.org] of 1.3, meaning they were 1.3 times more likely to be diagnosed with indications of dementia). Physical activity lowered the risks very slightly. In contrast, computer use lowered the risk by quite a bit more, dropping the hazard ratio to 0.8.

The same trend held when the researchers divided the group into thirds and compared high, medium, and low TV viewing and computer use. Controlling for additional factors like diet, alcohol use, and obesity didn't change the outcome either.

Although the impact of physical activity was minor, the researchers tested whether it might offset some of the problems associated with high TV viewing or low computer use. High levels of exercise appear to have a somewhat protective effect, but it's a minor one.

Overall, the results suggest that we need to separate how we think about the problems associated with sedentary activity. In terms of physical health, any type of inactivity may be roughly equivalent. But regarding mental issues, how you spend your inactivity matters—some means of being a couch potato involve passive consumption, and others involve a greater degree of mental activity.

In this sense, the results fit neatly into a large body of research that indicates that remaining mentally active can provide a degree of protection from dementia. Things like reading and playing vocabulary games appear to generally reduce dementia risk, and the benefits seem to build up even if the reading happens when people are relatively young. So, there's some reason not to be surprised by this general outcome.

That said, there are still a fair number of reasons for caution. Among other potential issues, the researchers note that activity levels were only checked at one point in the participants' history and were self-reported, which tends to be less accurate. It's also important to recognize that computer time will include a vast range of activities, some significantly more involved than others. So still some work to do here. But the next time someone yells at you for wasting time reading Ars, you can tell them you're protecting your mental health.

Journal Reference:
Just a moment..., (DOI: 10.1073/pnas.2206931119 [doi.org])

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