Watching four or more hours of TV a day could increase risk of bowel cancer in men, claims study

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Watching more than four hours of TV a day could put men at higher risk of developing bowel cancer, a new study suggests.

Past studies have shown that greater levels of physical activity can lower the risk of bowel cancer; now, a team of British researchers has examined the consistency of this link in a large study involving more than 430,000 men and women.

They found that sedentary behaviour, such as excessive TV-watching and computer use, was associated with a 35 per cent increased risk of developing bowel cancer in men but not women.

“Previous research suggests that watching TV may be associated with other behaviours, such as smoking, drinking and snacking more, and we know that these things can increase the risk of bowel cancer,” explains lead author Dr Neil Murphy of the International Agency for Research on Cancer (IARC) in France.

He added that being sedentary is also often linked to weight gain and higher amounts of body fat.

"Excess body fat may influence the blood levels of hormones and other chemicals which affect the way our cells grow, and can increase bowel cancer risk,” he said.

Bowel cancer is the fourth most common cancer in the UK.

"It starts in the large bowel (colon) or back passage (rectum)," explains Emma Shields from Cancer Research UK.

If it's spotted early, more than ninety per cent of people will survive the disease for at least five years, she told The Independent.

"So it’s important to know what’s normal for your body and tell your doctor if you notice any unusual or lasting changes," she added.

"These probably won’t mean it's cancer. But if it is, getting it diagnosed and treated early can make a real difference.”

The research, which was published in the British Journal of Cancer, is one of the largest to date to analyse the links between bowel cancer and sedentary habits.

However, it's crucial to realise that association does not necessarily mean causation in this instance, notes Paul Pharoah, professor of cancer epidemiology at the University of Cambridge.

"This study has not demonstrated that watching TV increases the risk of bowel cancer, it has demonstrated that time spent watching TV is associated with the risk of bowel cancer," he said.

“The findings from this study are not novel. It has long been known that physical activity is associated with a reduced risk of colon cancer, and this study confirms this association."

For professor Linda Bauld, prevention expert at Cancer Research UK, one of the study’s most interesting findings was that screen time had little to no effect, despite it being as sedentary an activity as watching TV.

This, she suggests, might be because we’re more in control of what we view in terms of content on a computer, whereas the TV watching experience is usually littered with adverts that we can't control which may exacerbate sedentary habits.

“There is evidence that greater exposure to TV junk food adverts increases the likelihood of eating more, which will also increase your chances of becoming overweight,” she explained.

She also highlighted the study's gender disparity:

“It’s interesting that only men who watched a lot of TV had an increased risk of bowel cancer, but not women. The study didn’t look at this directly, but it could be because men might smoke, drink and eat more unhealthily than women while watching TV," she said.

“We’ll need further research to answer the questions this study raises. What we do know is that keeping a healthy weight, cutting back on alcohol, being physically active and eating a diet rich in fruit and vegetables are known to cut your risk of bowel cancer.”