Results of a new study by the American Cancer Society show that around 12 per cent of colorectal cancer deaths in the US are attributable to smoking.

The prospective US study began in 1982, and included 312,000 men and 469,000 women. Individuals who were smokers at the start of the study had an increased risk of death from colorectal cancer compared with those who never smoked.

Colorectal cancer is not currently listed by any national or international organisations as a smoking related cancer. But, with more than 130,000 new cases and 56,000 deaths from colorectal cancer each year in the US, a large number of people may be affected.

In the past, studies have failed to find a link between cigarettes and colorectal cancer. However, this study suggests a lag of 30-40 years between the initial damage caused by the carcinogens in cigarette smoke and the development of colorectal cancer.

For male smokers, the risk of developing cancer was 1.32 times greater than in non smokers. For women, it was slightly higher at 1.41.

Those who quit smoking during the trial had a significantly reduced risk of death from colorectal cancer. If ex smokers also increased their physical activity and changed their diets, the risk was reduced even further (J Natl Cancer Inst, 2000, 92: 1888-96).