Monday, October 27, 2014

Breaks in Sedentary Time

There are two, no three, disease or health related lifestyle factors that I pay the most attention to when scanning research updates: dietary intake, tobacco use and sedentary behavior.  Sedentary behavior is any activity that keeps the body relatively still, e.g., sitting  and- typing a blog post, watching TV, playing cards, reading a book, listening to an instructor/speaker, playing video games.  Past research has shown that the more a person sits the worse it is for their health, with health defined as all-cause mortality, chronic disease, metabolic dysfunction (high blood pressure, blood sugar, etc.).  I have already talked about the past studies, but to review (and I don’t recall who was in the sample studied, i.e., men, women, young, old, black, white), sitting for more than an hour without taking a break -getting up and moving - is associated with poor health outcomes and this is still true (with a weaker effect) if the person doing the uninterrupted sitting also exercises for an hour or so a day.  So physical activity is good, sedentary behavior is bad, and sedentary behavior is bad (deleterious) for inactive AND active people.

So that was old news.  This week I read another study about the benefits of breaking up sedentary time.  The study by Sardinha, Santos, Silva, Baptista, & Owen (2014) specifically focused on Portuguese adults between the ages of 65 and 94, but it is likely that the same metabolic processes happen in older adults of other races/nationalities though the effect may be higher or lower.  An example; if sedentary behavior increased the risk of all-cause mortality by 2% in one group, it would probably increase the risk in a similar group, but the increase (effect) might be 1% or 5% instead.  Sedentary behavior is still bad, just more or less so.

The current study was a little different from those that came before, and that is a good thing, because it makes the evidence stronger.  Here the researchers included measures specific to an older person’s physical activity level, physical functioning and physical independence.  The participants wore accelerometers on their hips during the day for four days.  The accelerators recorded information on movement that the researchers could turn into activity levels.  The researchers took several measures of physical functioning, including, how many times a person could sit and stand from a chair in 30sec, how many dumbbell curls they could do in 30sec, and how far they could walk in 6 minutes.  The researchers measured physical independence with a 12 item scale with a total of 0 to 24 points.  Items include questions about one’s ability to do an activity with or without assistance, e.g., bathe, do laundry, walk, etc.  I found an example of both tests, if you’d like to see them click here for the physical function test and here for independence test.

For the outcome of interest, Sardinha et al focused on differences in persons’ physical functioning abilities (e.g., the dumbbell activity) and a score that totaled all those physical function abilities. These measures matter because they are important indicators of successful vs usual aging.  Sardinha et al compared the functional measures, while controlling for persons’ physical activity levels (do they get the recommend 30 minutes a day of moderate to vigorous physical activity/ yes or no; based on the accelerometer data), independence test scores (described in the above paragraph), BMI, sex and some other things.  They wanted to see if peoples’ scores were different based on the amount of time they spent in sedentary behavior (sb) and whether or not that time is broken up; breaks in sedentary behavior (BST).

And of course, the scores were different.  In the analysis of the physical function components and the overall score, there were higher scores in the dumbbell curl, the chair test and the overall score, when people took breaks in their sedentary time. The researchers also looked at the direct and independent effect of moderate-vigorous physical activity (cycling, aerobics, running), sedentary time and breaks in sedentary time on the total physical function score and found that people who engage in at least 30 min of moderate to vigorous physical activity a day have higher scores, people who spend the most time in sedentary behavior have the lowest scores and those who take breaks have higher scores than those who do not.

I leave you with a quote from the authors’ conclusion section:
Therefore, PA [physical activity] guidelines for older adults might emphasize more strongly these two distinct behaviors to be considered together, such that even if a person were to comply with 30 min/d of MVPA, they should avoid too much sitting for the rest of the day. Periodic and small interruptions to SB [sedentary behavior] are likely to be of importance in preventing a decline in physical function.

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