BY David Liu, PHD

Friday Aug 3, 2012 (foodconsumer.org) -- Tobacco use has been recognized as a risk factor for for colorectal cancer.  A new study in Carcinogenesis confirmed that glutathione S-transferases (GSTs) is involved in the detoxification of procarcinogens found in tobacco smoke including polycyclic aromatic hydrocarbons and heterocyclic aromatic amines.

The study led by W.P. Koh of National University of Singapore in Singapore and colleagues found GST gene polymorphisms determine an individual susceptibility to tobacco-smoke-associated colorectal cancer.

For the study, the researchers determined the deletion polymorphisms of GSTM1 and GSTT1 and the functional polymorphism at codon 105 of GSTP1 for each of 480 patients with colorectal cancer and 1,167 controls who did not have the disease.  All subjects were enrolled in the Singapore Chinese health Study in which 63,257 men and women had been followed since 1993.

It was found that of subjects who had no at-risk  GST genotypes, tobacco users were not at risk for colorectal cancer whereas among subjects who had two to three at-risk GST genotypes, tobacco users were at statistically significantly increased risk of developing colorectal cancer, compared to non-tobacco users. 

Among those who had two to three at-risk GST genotypes, tobacco users were more than five times as likely as those who never smoked to develop colorectal cancer.

Tobacco users who had one at-risk GST genotype were at a significantly increased but weaker risk of developing colorectal cancer, compared to non-smokers.

Procarcinogens in tobacco smoke have been known to be substrates for GST enzymes.

Colorectal cancer, a combination of colon cancer and rectal cancer, forms in the tissues of the colon. Most colon cancers are adenocarcinomas, according to the National Cancer Institute.   

Colon cancer and rectal cancer are  expected to be diagnosed in 103,170 and 40,290 people respectively in the U.S. in the year of 2012.  Colorectal cancer is expected to kill 51,690 men and women in 2012 in the US.

Colorectal cancer is largely preventable.  Factors that may be protective against the disease include dietary fiber, health weight, green tea, sufficient dietary folate, sufficient vitamin D, walnuts and flaxseed, yogurt, cocoa, garlic, curcumin, and physical activity.

Factors that may promote colorectal cancer include high fat diet, low carb diet, tobacco, alcohol, belly fat, or obesity, red meat and processed meat.