Does watching TV give you cancer? Of course not

2013 is just over a week old, and yet scaremongers are already bombarding us with warnings about the deleterious health effects of what we eat and drink. Now they’re turning their attention to children – not only in terms of what we feed them, but also in terms of what we allow them to do with their time.

Alarming newspaper headlines this week told us, ‘Children glued to TV and computer screens at increased risk of cancer and obesity’ or ‘New cancer warning over rise of obese “TV addict” British children’. According to the UK Mirror: ‘Experts have long been concerned about inactive children and obesity, but the World Cancer Research Fund (WCRF) has issued a fresh warning over kids who exercise and still turn to games and the TV.’ Apparently, even these kids are being made sick as a result of insufficient levels of activity.

I looked at the press release issued by WCRF, to find out what its ‘fresh warning’ was based on. It wasn’t based on any new research. The only report it referred to was one of WCRF’s own reports from 2007, titled Food, Nutrition, Physical Activity and the Prevention of Cancer: A Global Perspective. It seems WCRF just wanted to stick its oar in – alongside all the other advice being shoved down our throats – while ‘New Year resolutions are considered’.

Kate Mendoza, head of health information at WCRF, said: ‘People often assume that sedentary behaviour is the same as physical inactivity. But someone can do the recommended amount of daily physical activity but still be sedentary – for example, by spending an hour at the gym, then sitting at their desk all day and on the sofa in the evening.’ Apparently, WCRF’s 2007 report ‘found convincing scientific evidence that sedentary living causes weight gain and obesity, the second biggest cancer risk factor after smoking’. But did it, really?

In 2007, WCRF asked a panel of experts to review a wealth of evidence, including on whether sedentary living is a causal factor in ‘weight gain, overweight, and obesity’. The experts concluded that the evidence for a causal relationship was ‘convincing’. However, the only study of the relationship between sedentary living and weight gain in children that was reviewed in that 2007 report was a randomised controlled trial in rural upstate New York, which found no statistically significant link between TV viewing and body mass index (BMI). The New York study, covered in Archives of Paediatrics and Adolescent Medicine in 2004, was centred on an intervention designed to reduce TV viewing among children in 16 preschools and daycare centres. The results showed a reduction in TV viewing of 3.1 hours a week for the intervention group, and an increase of 1.6 hours a week for the control group. But there were no statistically significant differences in children’s weight gain or BMI between the two groups.

The 2007 WCRF report also reviewed studies on the relationship between physical activity and cancer in adults. It said that the evidence for physical activity having a modifying effect on colon cancer was, according to the panel of experts, ‘convincing’. For breast cancer it was ‘probable’; for lung cancer it was ‘limited’; and for other cancers the modifying effect of physical activity was ‘unlikely’.

So how did the panel of experts decide that the evidence for physical activity having a modifying effect on colon cancer was ‘convincing’? Of the 11 studies on the relationship between physical activity and colon cancer that were reviewed, eight reported a decreased risk of colon cancer for those in the highest physical activity groups compared with those in the lowest activity groups. However, the differences were only statistically significant in three of these eight studies. This means that in the other five studies, the differences between the most physically active and the least physically active were likely due to chance.

But even when one looks at the studies that found a statistically significant difference between the two activity groups, things are far from terrifying. One of the studies found that where 0.14 per cent of the most physically active men went on to develop colon cancer in the course of the 28-year study, 0.24 per cent of the least physically active men got the disease. (There was no statistically significant difference for females.) What these figures really reveal is that the chances of getting colon cancer are thankfully very low, whether or not one is physically active.

What about the claim that obesity is the second biggest cancer risk factor, after smoking? WCRF refers to numerous journal articles that show associations between obesity and cancer. It may well be true that excess body fat increases one’s risk of getting certain cancers; but it could also be the case that fat protects against other cancers. As Timandra Harkness pointed out on spiked earlier this week, a recent large-scale meta-analysis of 97 studies revealed that ‘the overweight [are] six per cent less likely than the normal to die while being studied’. The truth is that there is not a straightforward, easily measurable relationship between diet, weight, lifestyle and morbidity.

So how did not very statistically significant studies into the health of both children and adults carried out over many years get bundled up into neat and scary-sounding news reports about TV-watching children being ‘at risk of cancer’? This is how scaremongering looks set to work in 2013: various, sometimes vague pieces of medical research are wrung as hard as possible for ‘evidence’ that how we live our lives and how we raise our children is making us ill.

But we shouldn’t let scientists or public-health evangelists tell us how to live. Rather, we should make choices based on what we enjoy doing. By all means take up running or five-a-side football, if it makes you feel good; but don’t tie yourself in knots trying to stave off disease by carrying out the allegedly perfect amount of physical activity demanded by experts.

The philosopher Julian Baggini made a very simple but important point in an article last week. ‘Count less and think more’, he said. ‘Trying to keep up with health advice can feel like surfing the net for weather forecasts: what you find is always changing, often contradictory and rarely encouraging.’ Indeed. In 2013, we should resolve to worry less about what we eat, how much TV we watch and how much exercise we do, and enjoy life instead. And that’s the message we should give our children, too, rather than teaching them to fret about how much they weigh or how long they spend relaxing. The WCRF report is just another example of experts and charities manipulating statistics to promote their own moral message.

First published on spiked, 10 January 2013.