Associations between 5,10‐methylenetetrahydrofolate reductase codon 677 and 1298 genetic polymorphisms and environmental factors with reference to susceptibility to colorectal cancer: A case‐control study in an Indian population

Although the incidence rate of colorectal cancer is very low, and rectal cancer remains more common in India, a significant increase in its incidence has been reported for both men and women over the last 2 decades. We evaluated MTHFR genetic susceptibility and common environmental risk factors in the development of colon and rectal cancer, and assessed the interactions between gene and environmental factors with colorectal cancer in a case-control study in the Indian population. The study included 59 colon cancer cases, 243 rectal cancer cases and 291 controls. The variant MTHFR 677T allele is rare, while the 1298C allele is common among Indians. MTHFR 677T showed no association with colon cancer (OR = 0.82; 95% CI 0.28-2.05) and a nonstatistically significantly elevated risk with rectal cancer (OR = 1.51; 95% CI 0.86-2.68), and MTHFR 1298 CC genotype was found to be associated with a significantly decreased risk for both colon cancer (OR = 0.30, 95% CI 0.09-0.81) and rectal cancer (OR = 0.43, 95% CI 0.23-0.80). High intake of nonfried vegetables or fruits was inversely associated with both colon and rectal cancer risk. Especially, the combination of a high intake of nonfried vegetables and MTHFR 1298CC genotype was associated with the lowest rectal cancer risk (OR = 0.22, 95% CI 0.09-0.52). Regarding alcohol consumption, indigenous Indian alcohol drinkers (OR = 2.26, 95% CI 0.86-6.36), and those consuming alcohol for duration more than 20 years (OR = 1.55, 95% CI 0.73-3.33), were at a somewhat higher rectal cancer risk. Moreover, the consumed alcohol amount (gram-years) may be also associated with colon or rectal cancer risk.