BACKGROUND: Certain studies suggest that alcohol may reduce the risk of thyroid cancer in women, but the effect in men remains unclear. METHODS: We analysed the association between alcohol and thyroid cancer in a large (n ¼ 490 159) prospective NIH-AARP Diet and Health Study with self-reported beer, wine, and liquor intakes. RESULTS: Over 7.5 years of follow-up (median), 170 men and 200 women developed thyroid cancer. Overall, the thyroid cancer risk decreased with greater alcohol consumption (X2 drinks per day vs none, relative risk ¼ 0.57, 95% CI 0.36 -0.89, P-trend ¼ 0.01). CONCLUSIONS: These results suggest a potential protective role for alcohol consumption in thyroid cancer. The rapid increase in thyroid cancer incidence in the United States over the past three decades may be related to changes in certain environmental exposures, as well as increased surveillance and more widespread use of sensitive diagnostic tools (Enewold et al, 2009). However, despite many retrospective studies, few risk factors have been established other than childhood exposure to ionizing radiation (Dal Maso et al, 2009).Certain studies have suggested an inverse association between alcohol and thyroid cancer risk, but this may be confounded by cigarette smoking, which is correlated with alcohol consumption and has been inversely related with thyroid cancer (Mack et al, 2003;Jee et al, 2004;Nagano et al, 2007). However, no association was observed in a pooled analysis of 14 case -control studies after adjusting for smoking (Mack et al, 2003), or in two prospective studies with fewer than 200 cases (Iribarren et al, 2001;Navarro Silvera et al, 2005), although these studies were consistent with a small reduction in risk. A larger prospective study in women (421 cases) showed a clear reduction in risk with greater alcohol consumption (Allen et al, 2009). Although it remains unclear whether an association between alcohol and thyroid cancer exists independently of smoking, there is also a need to investigate effect modification by sex, given the three-fold higher incidence of thyroid cancer in women compared with men (Jemal et al, 2008). Given the evidence of a possible association and a recent decrease in alcohol consumption in the United States (Zhang et al, 2008;Kerr et al, 2009), we analysed the association between alcohol intake and the risk of thyroid cancer and its sub-types in a large US prospective study of over 490 000 participants, including more than 292 000 men.
MATERIALS AND METHODSThe NIH-AARP Diet and Health Study began in 1995 -1996 when a questionnaire was mailed to AARP members, aged 50 -71 years, residing in six US states (California, Florida, Louisiana, New Jersey, North Carolina, and Pennsylvania) and two metropolitan areas (Atlanta and Detroit; Schatzkin et al, 2001). Participant mailings and annual linkage to 11 state cancer registries and the National Death Index provide information on cancer and mortality outcomes. The NIH-AARP Study was approved by the special studies institutional review board of the US Nation...