Iodine is a suspected risk factor for thyroid cancer. Seaweed accounts for about 80% of Japanese people’s iodine intake. We examined the association between seaweed consumption and the risk of thyroid cancer in Japanese women. Women participating in the Japan Public Health Center-based Prospective Study (n=52 679; age: 40–69 years) were followed up for a mean of 14.5 years; 134 new thyroid cancer cases, including 113 papillary carcinoma cases, were identified. Seaweed consumption was assessed using a food-frequency questionnaire and divided into three categories: 2 days/week or less (reference); 3–4 days/week; and almost daily. The Cox proportional hazards model was applied to estimate hazard ratios (HRs) and 95% confidence intervals (CIs). Seaweed consumption was clearly associated with an increased risk of papillary carcinoma (HR for almost daily consumption compared with 2 days/week or less=1.71; 95% CI: 1.01–2.90; trend P=0.04). After stratification for menopausal status, an increased risk was observed in postmenopausal women (papillary carcinoma HR for almost daily consumption compared with 2 days/week or less=3.81, 95% CI: 1.67–8.68; trend P<0.01), but not in premenopausal women (HR=0.91, 95% CI: 0.44–1.91; trend P=0.76). This study identified a positive association between seaweed consumption and the risk of thyroid cancer (especially for papillary carcinoma) in postmenopausal women.
aEpidemiology and Prevention Division, Research Center for Cancer Prevention and Screening, National Cancer Center, Tokyo
bEnvironmental Epidemiology Section, Center for Environmental Health Sciences, National Institute for Environmental Studies, Tsukuba, Japan
Correspondence to Manami Inoue, MD, PhD, Epidemiology and Prevention Division, Research Center for Cancer Prevention and Screening, National Cancer Center, 5-1-1 Tsukiji Chuo-ku, Tokyo 104 0045, Japan Tel: +81 335 475 201 x3389; fax: +81 335 478 578; e-mail: firstname.lastname@example.org
Received June 30, 2011
Accepted July 1, 2011