Clinical Pearls:
- Intense to moderate physical activity for 60-75 minutes’ can eliminate the effects of prolonged sitting (> 8 hours).
- This equals to brisk walking at 5.6 km/h or cycling for pleasure at 16 km/h.
The association
of sedentary lifestyle and many chronic conditions and colorectal cancer is
well known and physical inactivity is an important modifiable risk factors in
the causation of many chronic condition. Prolonged sitting is one of the important
cause of premature mortality.
But,
according to a Meta-analysis involving about a million people, intense to
moderate physical activity for 60-75 minutes’ can undermine the effects of
prolonged sitting. This study was published online in the Lancet on July 27,
2016.[1]
Examples of physical activity were brisk walking at 5.6 km/h or cycling for
pleasure at 16 km/h.
This is a
second in the series of articles published on physical inactivity by Lancet, the
first was published in 2012, sending a message that physical inactivity is a
global pandemic killer-responsible for 5.3 million premature deaths worldwide.
The number equals the deaths caused by smoking and twice the deaths caused by
obesity.
This is the
first harmonized meta-analysis that compares the relationship between all-cause
mortality and sedentary life style and different levels of physical inactivity.
A systematic
review of literature identified about 16 studies out of which 13 were
identified by the researchers as providing data on sitting time and all-cause
mortality.
The combined
study data generated data on pool of 1,005,791 individuals from different
countries, who were followed up for 2-18 years.
The study
participants were divided into quartiles according to the time spent being physically
active and ranged from less than 5 minutes/day to 60-75 minutes/day. The daily
sitting and TV viewing time was also divided into 4 standardized protocol.
It was seen
that those who very active (60-75 minutes/day), the amount of sitting time does
not increase the mortality. But, the risk of death increases as the activity
time decreases. WHO guidelines also recommends at least 150 minutes of physical
activity per week, which is far less than what the study recommends.[2]
"A
clear dose-response association was observed, with an almost curvilinear
augmented risk for all-cause mortality with increased sitting time in
combination with lower levels of activity," the researchers noted.
For the
purpose of estimating the hazard ratio(HR), the most active individuals were
used as the reference group. (HR=1).
People who exercised
the least (less than 5 min/day) were at highest risk, even if they did not
spend much time sitting (less than 4 h/day). In this group the hazard of
premature death was 1.27. This was way higher than those group of individuals
who were most active physically (60-75 min/day) but also spent more than 8
hours sitting (HR=1.04). This was very close to the referent group, which led
the researchers to conclude that physical inactivity is the root cause of
premature deaths, independent of the hours of sitting.
The findings
of this study emphasized the importance of physical activity, even if you have
a job that demands prolonged sitting.
The study
also draws attention towards relationship with TV watching and premature death.
Watching TV for more than 3 hours per day is associated with premature death
regardless of physical activity except in the most active quartile. In this
group the mortality was only increased if you watch more than 5 hours of TV. The
benefit of physical activity is not very strong in people watching TV because of
“residual confounding”. Dr. Ekelund points that perhaps these people have unhealthy
life- style that include snacking or drinking that increases the risks.
Ekelund
pointed out in a London press conference [3]
that the average amount of time adults in the United Kingdom spend watching TV
is three hours and six minutes. “I don’t know if it’s too much to ask that
maybe a little of those three hours be devoted to physical activity,” he said.
The general rule of thumb, as Ekelund succinctly advised: “Sit less and move
more, and the more the better.”
He also
emphasized the message about "moving more," suggesting that people
should walk as much as they can and that if they do need to sit for prolonged
periods, they should break up those periods with short bursts of activity, such
as walking for 5 minutes every hour.
The full Lancet
podcast about the series can be heard here.
