Does sitting a lot increase my risk of cancer, even if I exercise?

Sitting a lot increases your risk of certain cancers, even if you exercise regularly. This has now been confirmed in several large analyses. The extra risk is not enormous, but it is measurable: roughly 7 to 29% higher risk depending on the type of cancer, and approximately 13% higher risk of cancer in general. Your chance of dying from cancer is about 18% higher if you spend a lot of time sitting.

The cancer types for which this association is most clearly apparent are uterine, ovarian, colon, breast, prostate and rectal cancer. For most of these, the evidence is considered 'suggestive': the association has been found repeatedly, but definitive causal proof in humans does not yet exist for all types. A genetic study on breast cancer provides stronger indications that the relationship is genuinely causal, not merely coincidental.

Exercise helps, but does not fully solve the problem. People who exercise a lot and sit a lot have a lower risk than someone who sits and does not exercise. Yet the risk is still higher than for someone who sits little. In other words: an hour of cycling in the morning does not cancel out the eight hours at your desk that follow. Sitting less and moving more are therefore complementary, not interchangeable choices.

Exercise, incidentally, has a well-proven protective effect on six types of cancer: bladder, breast, colon, uterine, oesophageal and stomach cancer. But those who exercise outdoors should pay attention to the sun: outdoor exercise is associated with a higher risk of melanoma, a serious form of skin cancer. Good sun protection is therefore not a minor consideration.