A prospective cohort study of body size and risk of head and neck cancers in the NIH-AARP Diet and Health Study.

Background:
The association between body size and head and neck cancers (HNCA) is unclear, partly because of the biases in case-control studies.

Methods:
In the prospective NIH-AARP cohort study, 218,854 participants (132,288 men and 86,566 women) aged 50-71, were cancer-free at baseline (1995 and 1996), and had valid anthropometric data. Cox proportional hazards regression was used to examine the associations between body size and HNCA, adjusted for current and past smoking habits, alcohol intake, education, race and fruit and vegetable consumption, and reported as hazard ratio (HR) and 95% confidence interval (CI).

Results:
Until 31 December 2006, 779 incident HNCA occurred: 342 in the oral cavity, 120 in the oro- and hypo-pharynx, 265 in the larynx, 12 in the nasopharynx, and 40 at overlapping sites. There was an inverse association between HNCA and body mass index, which was almost exclusively among current smokers (HR=0.76 per each 5 unit increase; 95%CI: 0.63-0.93), and diminished as initial years of follow-up were excluded. We observed a direct association with waist-to-hip ratio (HR=1.16 per 0.1 unit increase; 95%CI: 1.03-1.31), particularly for cancers of the oral cavity (HR=1.40; 95%CI: 1.17-1.67). Height was also directly associated with total head and neck cancers (p=0.02), and oro-and hypopharyngeal cancers (p<0.01).

Conclusions:
The risk of head and neck cancers was associated inversely with leanness among current smokers, and directly with abdominal obesity and height.

Impact:
Our study provides evidence that the association between leanness and risk of head and neck cancers may be due to effect modification by smoking.