On 4 October this year, A/Prof Emmanuel Stamatakis of
Sydney University released a study claiming that swapping just
1 hour of daily sitting with standing is linked to a 5% reduction
in the risk of premature death.
This is not so surprising. Stamatakis is an excellent and well-
respected epidemiologist, and we’ve heard the sitting message
before. Fore example, a large American study found that people
who sit more, and who sit for prolonged periods, are more likely
to have wider waists, higher blood fats, higher levels of inflam-
mation and greater overall risk of death.
What’s a little more surprising is that 1 month later
Stamatakis was a co-author of a study which found that in a
famous British cohort (Whitehall II), sitting was not associ-
ated with mortality risk after 16 years of follow-up. Neither
total sitting time, time spent watching TV, leisure time sitting
nor sitting at work had any relationship with the risk of death.
Stamatakis’ group concluded that policy-makers should be
cautious about recommending reductions in sitting time as a
stand-alone public health intervention.
What’s a person to believe these days? One day, milk is good
for you and your bones, the next it increases your risk of death
and fractures. Saturated fat is a killer one day, the next day it’s
almost a health food. Now we’re getting mixed messages about
sitting.
So what’s at the bottom of it all, so to speak? I think there
are two critical issues behind this uncertainty. The first has to
do with why sitting appears to have such bad health outcomes,
and the second has to do with the size of the effect.
Since the second issue is simpler, let’s start there. It’s easy to
recommend sitting less, but how much less do we need to sit?
One way of quantifying this is to ask what the trade-off is
between sitting and physical activity. How many minutes less
sitting do I need to do to get the same benefit as doing 10
minutes more exercise each day? There are several studies which
allow us to get a rough idea.
A recent analysis of a big American dataset found that in
terms of reducing cardiovascular risk in adults, 10 minutes of
physical activity was worth as much as 90 minutes less sitting.
Sir David Spiegelhalter, a biostatistician at Cambridge Univer-
sity, estimates that in terms of reducing all-cause mortality, 10
minutes more exercise is equivalent to about 2 hours less sitting.
A 12-nation study looking at the link between physical
activity, diet, sleep, sitting and obesity in kids found that kids
would need to sit for about 6 hours less to get the same obesity-
busting benefit as 10 more minutes of physical activity.
These figures are averages across the population, but the
benefits from sitting are far greater among people who are veryinactive. In fact, Stamatakis suggests that in the Whitehall
study, the failure to find an association between sitting and all-
cause mortality may be due in part to the fact that this cohort
was abnormally active.
This is what we also found in our analysis of sitting and
cardiovascular risk: people who get about 2 hours of physical
activity per day get virtually no extra benefit from sitting less,
a conclusion confirmed in a recent meta-analysis.
The more interesting and complex issue is that of the mech-
anisms behind the sitting–health link. Is it just because sitting
displaces other activities that are healthy (e.g. standing, light
physical activity, exercise, sleep)? And does it make any differ-
ence whether sittingdisplaces standing, light physical activity
or exercise? Or is it because there is something special about
sitting, such as the lack of muscular activity in the big muscles
of the legs?
A paper by the Franco-Scottish sedentary behaviour expert
Sébastien Chastin gives us some clues. Chastin used a radical
new statistical paradigm called compositional analysis, which
takes account of the fact that if we do less of one thing (sitting)
we must be doing more of something else (such as physical
activity).
Compositional analysis looks not at individual behaviours
but at mixes of behaviours called compositions. Using this
procedure, Chastin looked at the relationship between how
people spend their time and cardiometabolic risk in American
adults. A striking finding is that sitting, as part of the daily mix
of activities, has at best very weak associations with almost all
health outcomes (fatness, blood pressure, blood fats, inflam-
matory markers, blood sugar control). In particular, providing
you get a reasonable amount of physical activity (e.g. 30–50
minutes per day), it makes no difference whether you are sitting,
standing or doing light physical activity – for all outcomes
except blood insulin levels. Sitting is mainly harmful because it
displaces physical activity.
So here’s the bottom line, as I read it: if you’re reasonably
active you can forget about the standing desk, and needn’t feel
guilty about staying seated at meetings. If you’re relatively inac-
tive you’ll need to do an awful lot of standing for it to make
much difference. Standing, and light physical activity, may still
beat sitting if you have diabetes or pre-diabetes, or if you’re
very, very inactive.
All this means that it’s an uncomfortable time for sitting
researchers – they’re either sitting on the fence or walking both
sides of the street.42 | JAN/FEB 2016
Professor Tim Olds leads the Health and Use of Time Group at the Sansom Institute for
Health Research, University of South Australia.THE FIT Tim Olds
Now Even Sitting Researchers Are Sitting on the Fence
To sit or stand has become an uncomfortable question for health researchers.