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Lancet Series: Couch potatoes’ chips are up

10 Aug, 2012

In a post a while back I looked at the attempts to understand commuter behaviour in order to encourage active transport (e.g. cycling or walking). This is all very worthy but is there real value in the short periods of moderate exercise that this entails? “Absolutely” was the resounding answer in a thundering broadside by the Lancet a couple of weeks ago. More importantly, the researchers claim, the health impact of inactivity (as distinct from obesity) is on a par with smoking.

These bold claims were made in the Lancet Physical Activity Series, which went live with a flurry of media coverage. I went to the launch event at the London School of Hygiene and Tropical Medicine to explore the science behind the reporting. Lead researchers in the series presented their papers and a rousing call to arms from their young leader Dr Pedro Hallal.

The stated aim of the Lancet series is to “highlight clinically important topics and areas of health and medicine often overlooked by [the] mainstream”. The exposure of inactivity as a risk factor of similar magnitude to smoking is certainly radical. Headline figures report that a third of the world’s population is inactive, with a higher proportion in high-income countries. The global death toll of inactivity is estimated at an eye-watering 5.3 million deaths a year.

How could this danger have been overlooked for so long? Part of the reason is conflation with other factors. In the minds of the general public it is widely recognised that inactivity and a sedentary lifestyle is a bad thing, but this is normally linked implicitly with obesity. According to the researchers this is not the whole story.

In the first presentation of the day, Dr I-Min Lee from Harvard sought to demolish this assumption. Her paper reported the findings of an epic global meta-analysis seeking to quantify the burden of non-communicable diseases caused by inactivity worldwide. Careful to avoid the criticisms she had faced in the previous day’s press conference, she went to pains to validate her methods and emphasised the conservative bent of her findings.

The study focused on calculating the population attributable factor (PAF) for every country for which she could find dat. The PAF gives an indication of the impact a risk factor has on the prevalence of a disease in a population. The data she needed came from cohort studies recording activity levels and prevalence of non-communicable disease. Here overall aim was to build a global picture of health outcomes resulting from inactivity as a distinct risk factor.

The big challenge was to compensate for confounding factors. Obesity for example, is a big factor in the development of coronary heart disease. Is it possible that an inactive person at a healthy weight is still at greater risk than an active person? Given that obesity and inactivity are strongly linked, how do we disentangle the two factors?

Dr Lee’s approach was to go back to primary sources, where she could, to factor out other problematic variables. She was keen to emphasise the conservatism of her calculation, adding that it was probably an underestimate of the severity of the situation. For the UK she found that 16.9 per cent of all premature mortality was caused by inactivity. The diseases found to be affected included coronary heart disease, type 2 diabetes and breast cancer. If the problem were to be eradicated, overall life expectancy would rise by around a year.

The next presentation was by the project’s leader Dr Pedro Hallal, a Wellcome Trust New Investigator. He was keen to characterise the geographic and demographic spread of inactivity. This is where the claim that a third of the world population do not achieve their World Health Organisation recommended activity levels came from.

Hallal noted that the problem was much greater among women and adolescents. He also spoke about the strange dynamics between occupational and recreational exercise. Levels of physical activity are actually recovering in wealthy demographics (although they are still low), due largely to the increased fashionability of gym membership and recreational exercise. In poor populations, occupational activity is much more common, due to manual work and reduced car ownership. It is therefore the increasing numbers of urbanised low-to-middle income people who account for the bulk of the problem.

Being focused on epidemiology, there was little talk of the underlying biological mechanisms relating low activity to poor health. This did leave the audience with some questions. There was however, plenty of discussion of solutions. The proposals generally focused on coordinating policy over several sectors, including transport, urban planning and communication.

The researchers acknowledged that the general public is constantly bombarded with pleas to eat less, exercise more and wash behind their ears but with little avail. Recognising this, Dr Hallal was keen to point out that he and his colleagues were not seeking to be nannies. Respecting people choices was important to him, but they had to be given a real choice. However, he did call for more dedicated funding, stating “… physical activity is a stand-alone issue and needs to be treated like that”.

So what interventions can be implemented to make a difference? Most of the rest of the day tackled this question. The emphasis was on low-income countries and community-lead fitness programmes over public information broadcasting.

The message of the series is the same as ever – go and do some exercise. However, there has been a change in emphasis. Physical activity no longer needs to be seen as a grim sisyphean task, to keep weight-gain at bay. Instead it can be perceived as a positive, realistic way to improve ones health. The message is that relatively small amounts of exercise could have significant results in terms of life expectancy and quality of life.

Alternatively, you could subscribe the view presented in comments on the BBC News website: “I’m inclined to believe that the powers that be just want us fit and healthy so we can toil harder for the reptilian overlords which we will eventually succumb to…”

While the danger of reptilian overlords is still in question the threat posed by lounge lizards no longer is. With statistics as serious as those presented, the interventions discussed should not be considered as overzealous activities of a nanny state, just as good public health policy, like vaccination or anti-smoking campaigns.

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