Two UK studies have revealed the potential dangers to health from Western society’s increasingly sedentary lifestyles.
Both regular physical activity and avoiding inactivity help reduce build-up of dangerous liver fat, an important complication of obesity, according to one study.
“These findings reinforce the role of avoiding sedentary behaviour”
Its authors noted that role of exercise in the prevention and treatment of non-alcoholic fatty liver disease was well established.
But previous research had focused on the therapeutic benefit of increased moderate-vigorous activity, as opposed to habitual physical activity.
In their study, the authors investigated the influence of habitual physical activity on metabolic health and in particular, the amount of liver fat.
Volunteers with any level of physical activity were recruited. Participants were aged 18-60 years, and non-smokers with no history of diabetes, cardiovascular, kidney, respiratory or endocrine disease.
A total of 75 healthy people, with a mean age of 35 and body mass index of 25kg/m², were recruited by researchers led by Dr Dan Cuthbertson, from the University of Liverpool.
Their physical activity patterns were assessed using a SenseWear armband, while other factors were measured using magnetic resonance imaging and physical fitness testing.
Generic exercise running
Participants were categorised as healthy if they had two or less components of so-called “metabolic syndrome” – a cluster of conditions that can raise the risk of heart disease or stroke – and unhealthy if they had three or more. On this basis, 81% were judged to be healthy and 19% as unhealthy.
The authors found there was no significant difference in physical activity in terms of sedentary behaviour, number of steps or moderate-vigorous activity between metabolically healthy and unhealthy individuals.
However, the metabolically unhealthy individuals had significantly lower physical fitness and higher liver fat.
For example, they found that for every unit increase in % liver fat, the odds of being metabolically unhealthy increased by 37%.
In addition, for every one hour of increased sedentary time, liver fat increased by 0.87%, while for every daily increase of 1,000 steps, liver fat decreased by 0.87%.
Interestingly, the researchers said there was no significant association between hours of moderate-vigorous activity and liver fat.
They said: “In these individuals, sedentary behaviour and daily step counts are important determinants of the amount of liver fat and in turn of metabolic health status.
“These findings reinforce the role of avoiding sedentary behaviour even in the absence of increased MVPA,” they said in a poster (see attached PDF below) presented this week at the European Congress on Obesity in Porto.
The researchers added: “These data have shown that the amount of time we spend engaging in structured exercise does not predict health status.
“We reveal an emerging trend in overall physical activity levels that indicate moving about more throughout the day (for example breaking up long periods of sitting) is perhaps more important,” they said.
Meanwhile, a study by the same team, and also presented at the conference in Portugal (see attached PDF documents below), found just two weeks of inactivity in young healthy people could lead to changes that increased the risk of developing disease.
“People must avoid sitting for long periods of time”
They found that inactivity could reduce muscle mass and produce metabolic changes that could potentially lead to an increased risk of developing type 2 diabetes, heart disease, and potentially premature death.
Previous studies have focused on increasing habitual physical activity as an alternative to structured exercise, yet little is known about decreasing such activity, said the researchers.
In their study, they investigated the risk factors for developing disease after 14 days of physical inactivity. The study included 28 healthy, physically active – average 10,000 steps per day – people with a mean age of 25 years and a mean BMI of 25kg/m2.
All of the subjects wore a SenseWear armband to measure physical activity. They also had health checks including fat and muscle mass, mitochondrial function – to check their ability regulate their energy and recover from exercise – and physical fitness.
Assessments were done at the start of the study and after a 14-day step reduction protocol that reduced their activity by more than 80% to around 1,500 steps per day. They also kept a dietary journal to ensure no changes to food intake throughout the intervention.
“Just 14 days of increased sedentary behaviour resulted in small but significant reductions in fitness”
Analysis revealed that the step reduction protocol reduced moderate-to-vigorous activity, from a daily average of 161 min to 36 min – an average reduction of 125 minutes. At the same time, daily sedentary time increased by an average of 129 minutes.
Following the period of inactivity, significant changes in body composition were observed, including loss of skeletal muscle mass and increases in total body fat.
The changes in body fat tended to accumulate centrally, which is a major risk factor for developing chronic diseases.
Overall, cardio-respiratory fitness levels declined sharply and participants were unable to run for as long or at the same intensity as previously.
A substantial loss in skeletal muscle mass was also noted, with a reduction in both total lean mass (average 0.36kg) and leg lean mass (average 0.21kg). Mitochondrial function also declined but not significantly.
Dr Cuthbertson said: “In a group of physically active, healthy young individuals that met the recommended physical activity guidelines, just 14 days of increased sedentary behaviour resulted in small but significant reductions in fitness that were accompanied by reductions in muscle mass and increases in body fat.
“Such changes can lead to chronic metabolic disease and premature mortality,” he said. “The results emphasise the importance of remaining physically active, and highlight the dangerous consequences of continuous sedentary behaviour.”
He added: “Our day to day physical activity is key to abstaining from disease and health complications. People must avoid sitting for long periods of time.”