Long Term Effects on Health: is it the Sitting, or the Immobility?

Today I'll point out a study whose authors believe that the the fairly new consensus on sitting as a bad influence on long-term health is essentially mistaken. That there is a correlation between time spent sitting and mortality has been one of the more interesting results to emerge in recent years from the sea of statistical data on long-term health in humans. If this was just a matter of more time spent being sedentary correlating with higher mortality rates this would not be remarkable; that is the expected outcome in the middle range of the dose-response curve for moderate levels of exercise. No, what drew attention was the fact that time spent sitting seemed to be an independent risk factor for common causes of mortality, unrelated to the time spent exercising. In that model, you can be diligently jogging every day, but spend an extra hour in a chair while your equally diligent peers are standing and your life expectancy is worse.

If you look at the last five years you'll see a sudden blossoming of studies correlating time spent sitting down with telomere length, cancer rates, arterial stiffness, and all sorts of other measures of health and the slow slide into old age and disease. Given that people who are more sedentary do sit more we should probably take it as read that many of these studies are essentially unrelated to the interesting point above - they are picking up on the standard, well-worn correlation between poor health, lower life expectancy, and sedentary behavior. Still, some very large data sets show signs of this independent relationship between sitting and higher mortality rates.

One of the other interesting results to come out of large statistical studies of health in the past few years is the degree to which low levels of activity appear to make a difference. Things along the lines of puttering around in the garden or washing dishes have only been well quantified in large studies with the comparatively recent advent of low-cost accelerometers such as those present in mobile devices nowadays. With that data in hand, this sort of low-level exercise seems to be beneficial enough to need to be taken into account.

This leads us back to sitting: is it is the sitting, or is it the lack of puttering around that is contributing to this correlation, assuming that causation is involved and flows from the level of activity to quality of health? The researchers here argue that past conclusions on sitting are misinterpreting the issue, and immobility is the problem - sitting makes no difference if considered independently of exercise levels. That said, this is one study of a few thousand people, which at the moment is to be weighed against opposing studies with probably somewhere near a hundred times as many participants. As ever, more research is needed, but hopefully the whole business of how to eke out an extra year or three of health in old age via lifestyle choices of this sort will become a moot point soon enough to matter for those of us considering it today.

Sitting for long periods not bad for health

New research has challenged claims that sitting for long periods increases the risk of an early death even if you are otherwise physically active. The study followed more than 5000 participants for 16 years, making it one of the longest follow-up studies in this area of research, and found that sitting, either at home or at work, is not associated with an increased risk of dying. The participants included 3720 men and 1412 women drawn from the Whitehall II study cohort.

The study participants provided information on total sitting time and on four other specific types of sitting behaviour (sitting at work; during leisure time; while watching TV; and sitting during leisure time excluding TV) as well as details on daily walking and time spent engaged in moderate to vigorous physical activity. Age, gender, ethnicity, socioeconomic status, general health, smoking, alcohol consumption and diet were all taken into account. The study showed that over the 16 year follow-up period none of these five sitting measures influenced mortality risk. Future work will consider whether long periods of sitting are associated with increased incidence of diseases such as heart disease and type II diabetes, and will investigate the biological mechanisms that underpin previously observed associations between sitting time and health outcomes.

Associations of sitting behaviours with all-cause mortality over a 16-year follow-up: the Whitehall II study

Sitting behaviours have been linked with increased risk of all-cause mortality independent of moderate to vigorous physical activity (MVPA). Previous studies have tended to examine single indicators of sitting or all sitting behaviours combined. This study aims to enhance the evidence base by examining the type-specific prospective associations of four different sitting behaviours as well as total sitting with the risk of all-cause mortality.

Over 81,373 person-years of follow-up (mean follow-up time 15.7 ± 2.2 years) a total of 450 deaths were recorded. No associations were observed between any of the five sitting indicators and mortality risk, either in unadjusted models or models adjusted for covariates including MVPA. Sitting time was not associated with all-cause mortality risk. The results of this study suggest that policy makers and clinicians should be cautious about placing emphasis on sitting behaviour as a risk factor for mortality that is distinct from the effect of physical activity.

Comments

From my own little experience, I'd tend to think that sitting for long hours is the problem.

I've had the bad habit of sitting in front of the computer for many consecutive hours a day, for most of the day, and for a entire decade; I can attest that such behaviour has taken its toll on my back.

A physiotherapist recently told me how important it was to regularly switch positions. And advice that makes sense to me. Our bodies aren't optimised for sitting to begin with.

It'd be comparatively better to remain immobile - within alternating positions.

Posted by: Nico at October 14th, 2015 11:41 PM

The reason why a person is spending a lot of time sitting is also a potential factor. If, for example, it's because it's a necessary component of a job someone really hates, and they'd much rather be doing something else, their overall stress levels are going to be pretty high, and that stress is going to be quite damaging to health.

Posted by: Arcanyn at October 15th, 2015 10:41 AM

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