Not good for anything, including the digestive tract. (Photo: Colourbox)

Female smokers should consider colon cancer risk

Smoking is a recently established risk factor for colon cancer, especially for women − even when they smoke less than half as much as men.

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The added risk for women has been shown in a new study using Norwegian data.

Norway is among the countries with the highest rates of colon cancers.

The findings show that smokers of both sexes run higher a risk of a host of diseases, when compared to non-smokers.

But female habitual smokers run a 19 percent higher risk of contracting colon cancer than women who never smoke. Male smokers run an 8 percent higher risk than their non-smoking counterparts.

The results also indicate a 50 percent rise in risk among women who started puffing on smokes at age 16 or earlier.

An equivalent statistical warning bell tolls for women who have smoked for 40 years or more, according to a press release from the American Association for Cancer Research.

Half as much as men

Women appear to be susceptible to smoking-attributed colon cancer even when they smoke much less than men:

“Women who smoked 1-9 cigarettes a day had a significant 14 percent increased risk of colon cancer against non-smokers.”

“Men have to smoke 20 or more cigarettes daily, in other words over twice the amount, to experience a corresponding risk in relationship to non-smokers,” says Inger T. Gram, a professor in preventive medicine at the University of Tromsø (UiT).

Gram is also a chief physician at North Norway University Hospital.

She thinks the discovery regarding women who even smoke moderately tells us that smoking links to many more cases of colon cancer than anticipated.

“As colon cancer is a very common type of the disease, an increase in 14 percent tallies into lots of new cases of cancer that could have been avoided,” she says.

Followed an average of 14 years

Upwards of 600,000 Norwegian men and women aged 19 to 67 were included in the study.

It comprises data from four major health studies from 1972 to 2003. The medical researchers linked the information from these against data in the Cancer Registry of Norway.

The average follow-up of these participants was 14 years.

During this period nearly 4,000 new cases of colon cancer were diagnosed among the cohort group.

Special mutations found

The Norwegian professor points out that in the past 50 years cases of colon cancer have risen sharply among men and women on a global basis.

What’s the explanation for female smokers’ increased susceptibility to colon cancer?

“Tobacco smoke appears to result in special changes in cells on a molecular level. These lead to certain types of colon cancer. According to the study these changes occur more often in women than in men,” explains Gram.

She explains that such mutations are more often found in the ascending section of the colon.

“It was in this part of the colon on the right side that we found the big difference between men and women. So these results can explain the findings,” says Gram.

“Another, simpler, explanation is that the intestines of a woman are on average smaller than that of a man. The carcinogenic substances in a cigarette will thus have a higher concentration in the intestines of women than men,” writes Gram.

The results of the new study do not conclude decisively that smoking is a direct, sole cause of this type of cancer. 

The Cancer Registry points out that researchers in this field have been confounded in searching for a single principal cause. 

Several different factors probably act in concert, for instance life-style related risk factors such as obesity, alcohol consumption and inactivity. 

Other risk factors are intestinal polyps, small benign tumours, which develop without being detected or treated.


Read the Norwegian version of this article at

Translated by: Glenn Ostling

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