Do we really need epidemiology to tell us to get off our duffs?


The meme we hear in the news is that sedentary time, time spent sitting, is bad for us. I started out researching this week’s blog on inactivity, and ended up thinking about how to keep aspirations high and stay engaged with community.

Last week, the largest meta-analysis to date of inactivity was reported in the popular science press [for example]. The message is that even for people who exercise vigorously for part of each day, sitting still for long periods during the rest of the day poses an independent health risk. I found that evidence for this interpretation is weak. There is stronger evidence for the harm caused by sedentary behavior at the other end of the spectrum, for people who get little or no exercise.

I’ve been thinking about what that means, how “inactivity” is measured, and what we can do to avoid it.  I’m leaning toward the conclusion that getting up and moving frequently is good for us as part of a general program to avoid tunnel vision, to improve well-being and creativity even though the “independent mortality risk” is likely to be lost in the noise.

For people who don’t exercise at all, David Alter and colleagues at U of Toronto found a significant 46% additional mortality risk from too much time spent sitting.  But combining the statistical power of 41 separate studies, they found only an insignificant 16% added mortality risk for those with a vigorous exercise program.  In context 16% is not a lot–and here it was not statistically distinguishable from zero.  The failure of statistical significance in this case is not for lack of numbers, but because the different studies produced inconsistent results.

The reason 16% must be regarded as small is that all the different studies attempted to extract information about sedentary behavior from a diverse group of people who differed in many other ways. The statistical tool for separating out different causal factors is called “multivariate regression,” and it works reliably with 2 or 3 variables, but beyond this number, the statistical power is overwhelmed by the exponentially growing number of ways in which the different variables can interact.

Here’s what I mean (applied to the present case): All the studies here compiled were seeking information about time spent sitting, and how it might contribute to risk of mortality and disease. But the people being interviewed differed in many other ways as well, ways which had far more powerful effects on mortality risk than the time spent sitting. So for the study to produce meaningful results, it must disentangle such things as diet, obesity, exercise, family and social support, depression, and psychological passivity.

The researchers aren’t so dumb, so each of the studies that are included in this meta-analysis controls for just 2 or 3 other variables.  But these variables differ from one study to the next, making it hard for Alter and his team to draw meaningful generalizations.

Almost all these studies rely on self-reporting, which is notoriously inaccurate.  People are reluctant to admit how passive they are, and they are likely to be dishonest with themselves, let alone an anonymous researcher. The “good” response was supposed to be when people report less than 8 hours of sitting in a day. But what does this mean in a culture where our “society is engineered, physically and socially, to be sitting-centric.” [quote ref] Are these people who have jobs as sales clerks where they are on their feet all day, as opposed to desk jobs? Or are they just failing to mentally aggregate the time spent in a car, at a desk, at the kitchen table, and in front of the TV?

Translating the results into behavior change recommendations is also problematic.  The most obvious and frequently-recommended remedy is to get up from sitting, say once or twice in an hour, for some activity that gets the blood flowing.  But exactly none of the studies compared people who do this with people who sit through without getting up.  The questionnaires only asked about total time spent sitting.  We must take it on faith that briefly interrupting the sedentary period has benefits out of proportion to the time invested.

Though this is an article of faith (or theory – which is but another name for faith), I’m inclined to extend my faith in this direction.  In my own experience, while I’m reading or writing, I’m either pleasantly engaged in what I’m doing, or I’m in a stupor.  Either way, getting up to do something vigorous for a few minutes doesn’t seem at all appealing. But when I make the effort, it almost always invigorates me.  I come back, not just more alert, but often with a fresh idea or a change in my reference frame.

So I recommend taking 1 minute out of each hour for vigorous exercise, though I admit to finding this difficult myself. Getting up to think and walk is also something I can recommend from personal experience. The treadmill desk is something with which I have only vicarious experience.


Physical Passivity and Mental Passivity

About a third of the studies asked not about “time spent sitting” but about “time watching TV”.  In fact, TV has proven to be a robust predictor of mortality, with a clearer signal than the current emphasis on “sitting”.  Among the many studies in Alter’s meta-analysis, some of the largest effects came from those designed to study TV time, not sitting time.

Is there a difference between sitting behind a desk writing poetry, and sitting in front of a TV watching a program you don’t particularly like?  Emotional factors in mortality risk are huge, and depression is right up there.  Those who feel helpless and hopeless have far higher mortality risk than those who feel empowered, useful, and pro-active in their daily lives.

Watching TV brings on a dead state of mind for many people in our culture, who are numb while being passively entertained.  The relative risk for TV watching is far higher than the general risk of “sedentary behavior.” [ref].  Is mental passivity even worse than physical passivity?

In epidemiology and longevity studies, we have paid more attention to physilogical than to psychological variables, but psychology is at least as important. What is more, the physical and the mental are often difficult to disentangle, and there are other reasons to pay attention to the state of our wellbeing and empowerment and general satisfaction with life, even if there weren’t huge longevity benefits.

Depression is a huge risk factor for mortality–larger than obesity and sedentary life style combined.  Depression raises the risk of mortality by a factor of 3.1 for men, 1.7 for women [ref, ref].  For comparison, obesity (BMI>35) increases mortality by a factor 1.3 [ref]. Lack of exercise is associated with a similar risk factor of 1.3 in men and 1.4 in women [ref].

What is depression? I invite your comments on the subject.  I am convinced that depression is more a cultural than a psychological disease.  There are some countries in which depression is virtually unknown.  I think of depression as a lack of affect, a helplessness and detachment, a feeling that nothing I can do matters.  I imagine that the state of the American economy and politics contribute to feelings of isolation, disempowerment and hopelessness.

There is “clinical”, incapacitating depression that has afflicted people close to me.  Less extreme, there is walking through life like a zombie, afraid to feel and to act, unmotivated to change, unsure that anything that we do matters.  I have been there.  Closer to “normal” on the continuum, there is a general damping of the sense of wonder and zest for life that are our birthright.  Leaving this birthright behind, or at least putting it aside, seems to be a pre-condition for normal participation in work and social activities, (especially for white folks).  A video from The Onion helps me laugh about it.

From sedentary to television, from television to depression, from depression to powerlessness–these connections are my own, and I can’t claim the authority of science.  But I think they’re legitimate parts of the discussion if we’re looking for solutions that offer us more fulfilling lives on the way to health and longevity.  I welcome your perspectives in the comment section.


It doesn’t matter if I’m feeling blah, just so long as I’m not clinically depressed

Many of us in Western capitalist cultures not only have vague feelings of powerlessness, but we tend to feel powerless about our powerlessness.  We don’t want to think about it because there would seem to be nothing we can do about it. We don’t want to be stigmatized as a whiner, let alone as a psychiatric patient.

But the excesses of capitalism and the humdrum lives into which we are forced by economic conditions have profound effects on our wellbeing and also our longevity.  In other words, it’s not just that clinical depression has a huge effect on your health; the “subclinical” version that is so familiar to most of us is also harmful.  This is an understudied effect, because sublinical depression is the norm–what do you measure it against?  This week, another study from U of Toronto gave us a hint at how the subject can be approached.

Researchers have linked positive emotions–especially the awe we feel when touched by the beauty of nature, art and spirituality–with lower levels of pro-inflammatory cytokines, which are proteins that signal the immune system to work harder.

“Our findings demonstrate that positive emotions are associated with the markers of good health,” said Jennifer Stellar, a postdoctoral researcher at the University of Toronto and lead author of the study, which she conducted while at UC Berkeley. [Science Daily]

Interpolating between studies of depression and studies of inspired joy, I think there’s probably a continuum of psychological effect on health and longevity.

Elissa Epel shows us that feeling stuck in circumstances beyond our control accelerates aging of our telomeres, while meditation elongates telomeres.

I offer this in the spirit of an invitation, not an accusation: How many times have you experienced awe and wonder this week?  Why is it uncomfortable to even think about this question?  Why do we shrink from a perspective on life that may be expansively beautiful, but which interferes with our ability to play our familiar roles?

Can you be a better friend to yourself?


The Bottom Line

Your exercise program may be the most important factor for your mental health.

Get up and move because it interrupts your routine and encourages creativity, because it helps you feel empowered and connected.

Get your legs up in the air.  Renew the blood flow to your brain, and turn your habitual perspective on its head.

It’s reasonable to expect more from life than relief from depression and suffering.  Dare to reach for inspired joy.  Your life is an experiment.


This post originally appeared on Josh’s blog aging matters here.

Image: Shutterstock/Dave Clark Digital Photo