Thursday January 15 2015
Sitting down – the new smoking?
“Lack of exercise is twice as deadly as obesity,” The Daily Telegraph reports. The headline is prompted by a Europe-wide study on obesity, exercise and health outcomes.
Researchers wanted to see how many deaths could theoretically be avoided if inactive people became more active, compared to how many would be avoided if obese people lost weight.
Researchers calculated that if activity levels were increased so that no-one was classed as inactive, then this could reduce early deaths by more than 7%. This compares to avoiding obesity, which could reduce deaths by nearly 4%. In 2008, say the researchers, 676,000 deaths were attributable to physical inactivity, compared with 337,000 deaths attributable to obesity.
This large study also found that among inactive individuals, even small increases in activity may be of benefit, whatever their weight or waist size.
So should we concentrate purely on physical activity and stop worrying about losing weight?
In practice it’s hard to disentangle the two, since exercise, along with diet, helps maintain a healthy weight. Also, obesity is an established risk factor for diseases such as type 2 diabetes, which is best tackled with a combination of diet and exercise.
So it would be a bad idea to ignore the risks of obesity, whatever your levels of physical activity.
Where did the story come from?
The study was carried out by researchers from a number of academic centres in Europe, including the Universities of Cambridge, Oxford and London. It was funded by grants from many bodies across Europe, including the EU and in the UK the Department of Health, the Medical Research Council, Cancer Research UK, the Wellcome Trust, the Stroke Association, the British Heart Foundation and the Food Standards Agency.
The study was published in the peer-reviewed American Journal of Clinical Nutrition and has been made available on an open-access basis, so it is free to read online or download as a PDF.
It was covered fairly by the UK media, although the aims and design of the study were more complex than some of the reporting suggests.
What kind of research was this?
This was a large cohort study following 334,161 European men and women for an average of about 12 years, looking at levels of physical activity, body mass index (BMI) and waist circumference (a measure of abdominal adiposity) and the risk of early death.
The researchers say that lack of physical activity has long been associated with an increased risk of death, independent of people’s BMI. Their aim was to find out if either BMI or waist circumference had any influence on the association between physical activity and the risk of early death.
They also compared how many deaths could theoretically be avoided if inactive or obese individuals were more active or non-obese respectively.
What did the research involve?
The researchers used data from an ongoing European study (the EPIC study) of more than half a million participants from 23 centres in 10 countries – Sweden, Denmark, Norway, the Netherlands, the UK, France, Germany, Spain, Italy and Greece. They were recruited to the study between 1992 and 2000.
Participants were aged between 25 and 70. Those who reported having heart disease, stroke or cancer at recruitment were excluded from this current analysis, as were those with missing data in areas such as physical activity and lifestyle.
Participants’ height, weight and waist circumference were measured at the start of the study. From this data they were categorised as normal weight (BMI 18.5-24.9), overweight (BMI 25-30) or obese (BMI of 30 or over). For waist circumference researchers considered waist circumference to be high if over 102cm for men and over 88cm for women.
Participants self reported their levels of occupational, recreational and household physical activity, using a validated questionnaire. Levels of physical activity at work were categorised as either sedentary (e.g. office work), standing (e.g. hairdresser, security guard) or physical (e.g. plumber, nurse) or heavy manual work (e.g. bricklayer).
Recreational activity was assessed as the amount of hours per week spent cycling, jogging, swimming and other physical exercise.
The researchers assessed overall activity levels by combining occupational and recreational activity levels. Physical activity was then categorised into four groups:
- moderately active
- moderately inactive
Researchers collected data on participants’ death from all causes between 2008 and 2010 from official records in each country, both at the regional or national level.
They then examined associations between physical activity, obesity, waist circumference (WC) and deaths from all causes. They adjusted their results for sex, smoking, education and alcohol intake.
What were the basic results?
The analysis included 116,980 men (average age 52.6 years) and 217,181 women (average age 51.2 years). There were 11,086 deaths among the men and 10,352 deaths among the women.
The risk of early death was reduced by 16-30% in people were who moderately inactive, compared to those who were inactive, whatever their BMI or waist circumference.
In normal weight and overweight people, higher levels of physical activity were associated with a further reduction in risk.
The researchers calculate that avoiding all inactivity could theoretically reduce all-cause mortality by 7.35% (95% confidence interval (CI), 5.88-8.83%).
Avoiding obesity could theoretically reduce all-cause mortality by 3.66% (95% CI, 2.30-5.01%).
How did the researchers interpret the results?
The researchers say that the greatest reduction in risk of death was in the moderately inactive groups, compared to those who were totally inactive. This reduction in risk was found across all groups at all levels of BMI and waist size.
Physical inactivity may theoretically be responsible for twice as many deaths as a high BMI, they say.
Efforts to encourage even small increases in activity may be of benefit.
This study’s strengths included its large size and long follow-up period. Researchers also took into account a large number of factors (called confounders) that might have influenced the risk of death, such as diet, smoking history and alcohol intake, although it is still possible that both measured and unmeasured confounders influenced mortality rates.
The study had one important limitation. It only measured people’s BMI (calculated by combining their weight and height) and their physical activity once, at the start of the study. It is quite possible that people’s BMI changed over time, and that this would have had an effect on mortality rates. For example, if physical activity helped reduce obesity over time, it is not possible to say that physical activity reduced the risk of mortality, independent of people’s weight.
Also, the calculations on the number of deaths that could be avoided by both reductions in physical inactivity and obesity is hypothetical.
It would be a bad idea to ignore the risks of obesity, whatever your levels of physical activity.
Obesity is an established risk factor for a range of conditions such as diabetes and cardiovascular disease and it is best tackled by both diet and exercise. But no-one would argue with the notion that everyone should be encouraged to increase levels of physical activity, whatever their size.
An ideal way to gradually raise your activity levels is our Couch to 5K programme, which can turn a couch potato into a successful five kilometre runner over the course of nine weeks.
Analysis by Bazian. Edited by NHS Choices. Follow Behind the Headlines on Twitter. Join the Healthy Evidence forum.