Smoking is by far and away the single major cause of cancer, but being obese, drinking too much alcohol, having a poor diet and being physical inactive combined are the second major cause.
Overall, 42 per cent of the 659,640 new cancer cases reported in the US every year were directly caused by poor lifestyle, as were half the 265,000 annual cancer deaths, say researchers from the American Cancer Society.
And even this is likely to be an under-estimate of the real figures because lifestyle choices are hard to track, and there may also be other risk factors in the way we live that haven't yet been recognised as increasing the risk of cancer.
The researchers assessed the impact of lifestyle choices on 26 different cancers, and discovered that cigarette smoking alone was directly responsible for 19 per cent of all cancer cases reported every year, and nearly 29 per cent of all cancer deaths. Obesity was the next highest risk factor, responsible for nearly 8 per cent of cases, and excessive drinking, which was reckoned to cause nearly 6 per cent of cancers.
But there was a complex mix of factors at play, the researchers said, and a poor diet with too little fresh fruits and vegetables, dietary fibre, physical inactivity and infections all played a part.