Figure 1.

Hazard ratios (HRs) of head and neck cancer, and corresponding confidence intervals (95% CIs), according to pack-year of cigarette smoking and food folate intake (μg per day). The HRs were derived from Cox proportional hazard models, adjusting for age, sex, body mass index, education, race/ethnicity, pipe smoking status, cigar smoking status, pack-year cigarette smoking, alcohol drinking intensity, non-alcohol total energy, total vegetable and fruit intake. The number of cases and controls within each category was indicated below the corresponding HR as: ‘number of cases: number of cohorts’. We found no interaction between smoking and food folate intake on HNC risk.