People who smoke and drink appear to develop colon cancer earlier in life and should start screening for the disease sooner than others, an American study found.

Researchers at Northwestern University in Illinois performed an analysis of over 160,000 patients with colon cancer. They found that those who had smoked and drunk alcohol in the previous year developed the disease an average of eight years earlier than those who abstained from tobacco and alcohol.

The study, found in the March 27 issue of Archives of Internal Medicine, also suggested that those who drink but don't smoke, or smoke but don't drink, contracted the disease an average of five years earlier than people who never drank or smoked.

Women who smoked but didn't drink developed colon cancer an average of 6.3 years younger than women who never drank or smoked.

Doctors generally recommend screening for colon cancer for anyone 50 or older, as 90 per cent of cases occur in patients older than 50.

Screening can begin earlier if the patient has a family history of the disease. The researchers suggest that smoking and drinking could also warrant earlier screening.

Screening for the disease can be done by sigmoidoscopy, which checks for tumours in the lower intestine, and by colonoscopy, which is a more extensive examination using a flexible instrument inserted and threaded through the entire colon.

One in 14 men and one in 16 women is expected to develop colorectal cancer during their lifetime, the Canadian Cancer Society says.

The Canadian Cancer Society says colorectal cancer is the third most common cancer for both men and women in Canada, and the second leading cause of death from cancer.