How much exercise is enough?
How much exercise should we do?
I think we all know that it is important to stay physically active if we want to maintain our physical and mental well-being. But how much exercise is enough?
The NHS recommends 150 minutes of moderate or 75 minutes of vigorous exercise, spread over the week, for people aged 19 to 64.
For children, they suggest an average of 60 minutes of moderate to vigorous activity a day. But new research indicates that, actually, children need considerably more active time, if we are to reverse the plague of childhood obesity.
Obesity in youth can lead to disease and early death
Childhood and adolescent obesity are associated with cardiovascular, metabolic, neurological, and musculoskeletal diseases in adulthood. Moreover, childhood obesity was recently associated with an increased risk of premature death by the mid-forties.
Lifestyle changes such as reducing sedentary behaviour and physical inactivity may improve health but there is a shortage of really good data about this.
There is no information on the effectiveness of light physical activity in preventing obesity and how much sedentary time needs to be reduced for better health in the young population. These gaps in knowledge significantly limit current health guidelines.
Teenagers not reaching current guidelines
Recent reports concluded that more than 80% of adolescents across the globe do not meet the World Health Organisation’s recommended average of 60 minutes/day of moderate to vigorous exercise.
It is estimated that physical inactivity will have caused 500 million new cases of heart disease, obesity, diabetes or other noncommunicable diseases by 2030, costing US$ 27 billion annually.
This alarming forecast regarding the morbid danger of physical inactivity necessitates urgent research on the most effective preventive approach.
Challenges studying how much exercise is required
It is expensive and logistically challenging to accurately measure movement, total body fat mass and abdominal fat mass in children and young people, so this has not previously been studied.
The current project is both the largest and the longest follow-up study of objectively measured physical activity and fat mass in the world. It used the University of Bristol’s Children of the 90s data, and included 6,059 children aged 11 years, who were followed up until the age of 24 years.
Waist-worn accelerometer measures of sedentary time, light physical activity, and moderate to vigorous physical activity, and DEXA-measured fat mass and skeletal muscle mass were collected at ages 11, 15, and 24 years.
The children also had their fasting blood samples repeatedly measured for, glucose, insulin, high-density lipoprotein cholesterol, low-density lipoprotein cholesterol, triglyceride, and high-sensitivity C-reactive protein. In addition, blood pressure, heart rate, smoking status, socio-economic status, and family history of cardiovascular disease were measured and controlled for in the analyses.
More sitting, less activity observed
During the 13-year follow-up, sedentary time increased from approximately 6 hours a day in childhood to 9 hours a day in young adulthood. Light activity decreased from 6 hours a day to 3 hours a day, while moderate to vigorous exercise was relatively stable at around 50 minutes a day throughout.
It was observed that each 1-minute spent sedentary was associated with a 1.3-gram increase in total body fat mass. Both boys and girls gained an average of 10 kg of fat mass during growth from childhood until young adulthood.
However, sedentary time potentially contributed 700 grams to 1 kg of fat mass (approximately 7 – 10%) of the total fat mass gained during this time.
Every minute of light physical activity counted
Contrariwise, each 1-minute spent in LPA during growth from childhood through young adulthood was associated with a 3.6-gram reduction in total body fat mass. This implies that cumulative LPA decreased total body fat mass by 950 grams to 1.5 kg: approximately 9.5 – 15% decrease in overall fat gain during the 13-year observation period.
Of note, time spent engaging in moderate to vigorous exercise (including meeting the 60-minute/day recommended by the WHO) was associated with just 70 to 170 grams reduction in total body fat mass.
Virtually no benefits from more energetic activity
Andrew Agbaje, award-winning physician and paediatric clinical epidemiologist at the University of Eastern Finland says of the findings:
“Our study provides novel information that would be useful in updating future health guidelines and policy statements. Prior to this study, it has not been possible to quantify the long-term contribution of sedentary time to fat mass obesity and the magnitude by which PA may reduce it. Our study confirmed the report from a recent meta-analysis of 140 school-based randomised controlled trials across the globe that engaging in MVPA had minimal or no effect in reducing childhood BMI-obesity.
“We have also recently reported that LPA promotes healthy heart, lowers inflammation and lowers cholesterol levels among children, adolescents, and young adults better than MVPA. These new findings strongly emphasise that LPA may be an unsung hero in preventing fat mass obesity from early life, and in this regard, it could lower fat mass nearly 10 times more than MVPA, except that it requires at least 3 hours per day. Examples of LPA are long walks, house chores, slow dancing, slow swimming and slow bicycling.”
How much exercise is enough?
Instead of telling people to aim for an average of 60 minutes a day of moderate to vigorous exercise, the study suggests that they should be doing light activities for at least three hours a day. This appears to be the antidote to the unhealthy effects of sedentary time in the young population.
It is probably unhelpful to highlight that 80% of adolescents don’t meet current guidelines; rather, the health message should be that continued and sustained participation in light physical activity is the way to prevent childhood obesity.
You can read the full study here (external link will open in a new browser tab or window)
Hospital admissions have doubled
As a footnote, NHS data has just revealed that more than 3000 people are admitted to hospital every day due to obesity. This is a doubling of the number in six years. The figure includes admissions where obesity is a complicating factor. Pregnant women are particularly at risk for complications due to obesity.
For children, the figure is more than 20 a day.
These averages conceal wide regional variations between best and worst. Unsurprisingly, people in areas of high social deprivation are more affected by the scourge of obesity.
It is now estimated (by the Tony Blair Institute for Global Change) that obesity costs Britain £98 billion annually. This includes £19 billion in NHS expenses. An obese patient costs twice as much as one of healthy weight. The rest of the cost is mainly down to productivity losses as people become too sick to work due to obesity.
You can view the full data from NHS Digital here (external link will open in a new browser tab or window)
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Further reading and resources
Millennials are also affected by the obesity epidemic – you can read more about it here
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