Aug 01 2016

Exercise and Health

couchpotatoEveryone knows that it is better for your health to exercise regularly, and that a sedentary lifestyle is ultimately unhealthy. The science clearly supports this conclusion as well, so this is one area where popular belief and science are in accord.

Uncertainty sets in, however, when you try to drill down to more detail. The primary question is – can exercise undo or offset the negative effects of being sedentary? Is the problem with sitting only that you are not exercising, or is sitting a risk factor for death in and of itself?

A new review and reanalysis of data from 13 studies hopefully clarifies this question. There is some good and bad news in the results, but overall I think it is good.

The authors looked at the two variables of interest, exercise and sedentary time. Sedentary time includes driving, sitting at a desk, watching TV, and similar activity. Moderate exercise could be just taking a brisk walk, and they mostly considered the total time of exercise.

Not surprisingly, they found that exercise was associated with decreased risk of death from all causes in the 14 year follow up period, while time spent being sedentary was associated with increased risk of death.

But then they also looked at people who had sedentary jobs and hobbies, but also exercised. They found a decreased risk of death in this group. In fact, the risk of death in this group was lower than for those who did not have sedentary habits, but also did not exercise.

They conclude:

“High levels of moderate intensity physical activity (ie, about 60–75 min per day) seem to eliminate the increased risk of death associated with high sitting time. However, this high activity level attenuates, but does not eliminate the increased risk associated with high TV-viewing time. These results provide further evidence on the benefits of physical activity, particularly in societies where increasing numbers of people have to sit for long hours for work and may also inform future public health recommendations.”

So, if most of your sedentary time is sitting at a desk, you can essentially completely offset this with 60-75 minutes of moderate exercise per day. That is more than most people get, and could be difficult for most people to work into their schedule. The authors recommend that employers make it easier for their employees to grab some exercise during lunch, or immediately before or after work.

Less exercise is still extremely useful. Although it may not completely offset eight hours of desk work, even 20-30 minutes of exercise does reduce the negative effects. So the bottom line there is, do as much as you can with a goal of about an hour a day.

The other wrinkle in the data is that TV watching time is worse than desk time. The studies did not capture data that would tell them why there is this difference. They speculate that TV watching time may be associated with snacking or may be a marker for other bad health habits.

This makes some sense, as people have to work and their job may require sitting at a desk for long hours. People have more of a choice as to their TV watching time, and so that may be more predictive of other health lifestyle choices.

One obvious solution is – Pokemon Go. Seriously, this is a game many people find fun and requires a lot of walking around. To generalize this example, however, it helps to find fun and convenient activities that require at least not sitting, and preferably some physical activity like brisk walking.

TV watching is an easy pastime, and it’s easy to fall into a habit of relying on the TV for entertainment. If, on the other hand, you were in the habit of getting your entertainment on your feet that would reduce your risk of death.

As a general rule it is better (a more successful strategy) to improve your health by changing your default behavior or your habits, rather than using brute force will. The latter approach has a dismal record of success, generally less than 5% for pretty much any activity.

Hopefully we are entering out of the era of sedentary video and games and into an era of more virtual reality and augmented reality, which require physically moving. It remains to be seen what health effects this will have on the population, but I am hopeful.

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