Table 5.

Pooled Analysis Odds Ratios for Colorectal Cancer Risk Among Persons With the Methylenetetrahydrofolate Reductase (MTHFR) 677TT Genotype, by Tobacco Use^a

Tobacco Use	No. of Subjects	CC		CT		TT		CT vs. CC		TT vs. CC
		No.	%	No.	%	No.	%	ORb	95% CI	ORb	95% CI
Never smoking	4,321
Controls		1,235	44.67	1,150	41.59	380	13.74
Cases		694	44.60	665	42.74	197	12.66	1.03	0.90, 1.19	0.92	0.74, 1.13
≤14.2 pack-years of smoking	2,249
Controls		708	47.84	589	39.80	183	12.36
Cases		371	48.24	312	40.57	86	11.18	0.95	0.78, 1.16	0.84	0.62, 1.15
>14.2 pack-years of smoking	2,485
Controls		677	45.84	606	41.03	194	13.13
Cases		493	48.91	420	41.67	95	9.42	0.88	0.73, 1.05	0.60	0.45, 0.80

Abbreviations: CI, confidence interval; OR, odds ratio.

^aUnadjusted P value for interaction between tobacco use and MTHFR genotype: P = 0.43. Wald χ² test (2 df) P value, by tobacco use: never smoking—P = 0.54; ≤14.2 pack-years—P = 0.55; >14.2 pack-years—P = 0.0021.

^bAdjusted for age, sex, study, and ethnic group.