Sitting for hours on end is linked to nine more cancers than we thought, according to the cancer expert who is helping to re-write the exercise guidelines.
Charles E Matthews, an epidemiologist at the National Cancer Institute, warns we need more physical activity than we thought – but more importantly, we need to sit less.
Just one hour of TV a day puts even the most active of us at a higher risk of not just breast and colon cancer – which we already knew – but also nine other cancers including lung and head or neck.
Sharing the new research at a conference on Saturday, Dr Matthews said swapping your Netflix show for a brisk walk or some housework could be a game changer.
‘Watching TV is the major competitor to going out and being more active,’ he told the American Association for the Advancement of Science conference in Austin, Texas.
‘Think of light activity and sedentary behavior as flip-flopping each other.
‘This is where moderate activity like a brisk walk or things around the house come in. Anything that is not sitting is good.’
The latest physical activity guidelines for Americans, published in 2008, recommend ‘avoiding inactivity’, plus up to five hours a week of moderate activity and up to two-and-a-half hours a week of vigorous activity spread throughout the week.
Beyond staying trim, that exercise lowers risk of death from all factors, according to the National Institutes of Health.
Sedentary behavior is linked to early death from heart disease, stroke, type 2 diabetes, high blood pressures, falls, brain diseases, respiratory conditions and cancer.
Doing the minimum recommended – up to seven-and-a-half hours a week – reduced mortality risk by 20 percent in a recent cohort study.
But according to Dr Matthews, it has become clear in the last decade that eliminating risk ‘requires much more activity than we currently recommend… around four to five times the amount.’
This year, the National Cancer Institute, a branch of the NIH, is publishing an update to the decade-old guidelines, to answer ‘a lot of unresolved questions that weren’t addressed last time’.
One of the most pressing things Dr Matthews has been investigating is whether there is an upper limit to physical exercise. In other words: when do you plateau?
For the first time, they found that once you surpass 25 hours a week – around three-and-a-half hours a day – the effect is largely the same until you reach 75 hours a week, which is around the amount of time marathon runners train.
Even those who spend their evenings and weekends exercising, though, need to minimize their sitting time if they want to avoid sedentary-related health issues.
Dr Matthews’ research showed there is no way to eradicate risk, and even those who get the recommended amount of exercise have a higher risk if they watch just an hour of TV a day.
Let’s start small, he said.
‘Most people are sedentary 60 percent of the day. But that still leaves you four, five, six hours a day to be active,’ he said.
‘Clearly you get the most benefit by doing moderate or vigorous activity for an hour but there are many ways you can get up to a higher level. Reducing sitting and doing light activity can help.’