© 2002 Elsevier Science Inc. All rights reserved. 1047-2797/02/$–see front matter 655 Avenue of the Americas, New York, NY 10010 PII S1047-2797(01)00281-2 INTRODUCTION Thyroid cancer is a relatively rare tumor with a striking gender difference in age-adjusted incidence rates (3–4 times higher in females) and the pattern of age-specific in- cidence (1). The only two clear risk factors for thyroid can- cer are exposure to ionizing radiation and prior benign thyroid hyperplasias (including goiter and thyroid nodules) (1). Other factors investigated include dietary exposures af- fecting thyroid-related hormones and function, such as io- dine-rich seafood and goitrogenic vegetables (2–10), body weight and weight gain (9, 11–13), medical conditions and medications (7, 10), and smoking and alcohol consumption (14, 15). We conducted a thyroid cancer case-control study among women living in Los Angeles County. We have re- ported our findings on reproductive and hormonal expo- Lifestyle and Other Risk Factors for Thyroid Cancer in Los Angeles County Females WENDY J. MACK, PHD, SUSAN PRESTON-MARTIN, PHD, LESLIE BERNSTEIN, PHD, AND DAJUN QIAN, MS PURPOSE AND METHODS: We conducted a population-based case-control study of thyroid cancer. Cases were 292 women, aged 15–54 when diagnosed between the years 1980 and 1983 (145 diagnosed in 1980–81 and 147 diagnosed in 1982–83). Female neighborhood controls ( n = 292) were matched to each case on birth-year and race. RESULTS: Among women  35 years, thyroid disease in first-degree relatives increased thyroid cancer risk [odds ratio (OR) = 2.0, 95% confidence interval (CI) = 1.1–3.7]. Risk was not associated with fish consumption, although high childhood consumption of shellfish decreased thyroid cancer risk (OR = 0.2, 95% CI = 0.05–0.7 for consumption at least a few times weekly). Among papillary thyroid cancers (82% of cases), frequent adult consumption of saltwater fish decreased risk. Cancer risk was reduced with con- sumption of certain vegetables, wine, and tea. Other dietary variables, including milk, beer and hard li- quor, and coffee were not related to thyroid cancer risk. Among the papillary sample, risk increased with longer use of multivitamins (OR = 2.9, 95% CI = 1.2–7.4 for  10 years of use). Smoking and body mass were not associated with thyroid cancer risk. CONCLUSIONS: These results suggest a role of family history of thyroid disease and certain dietary variables in the etiology of thyroid cancer in adult females. Ann Epidemiol 2002;12:395–401. © 2002 Elsevier Science Inc. All rights reserved. KEY WORDS: Thyroid Neoplasms, Risk Factors, Diet, Pharmaceutical Preparations, Smoking, Body Weight, Alcohol Consumption. sures, exposures to therapeutic radiation, and history of benign thyroid diseases (16, 17). This paper reports findings regarding specific dietary exposures, body weight, smoking, and specific medical conditions and drugs. Data from this study was recently included as one of 14 case-control stud- ies used for a combined analysis of various risk factors for thyroid cancer (18). Our participation in this combined analysis made us aware that our data on the factors dis- cussed in this paper are of particular interest. Our data on these factors are more complete and provide more detail than similar data from many of the other studies and seemed, therefore, worthy of evaluation and reporting at this time. MATERIALS AND METHODS Cases All women diagnosed with histologically confirmed thyroid cancer between January 1, 1980 and December 31, 1983 who were aged 15 through 54 years at diagnosis were identi- fied through the Los Angeles County population-based registry, the University of Southern California Cancer Sur- veillance Program. The study was restricted to English- speaking white (including Latina) women born in the From the University of Southern California, Department of Preventive Medicine, Los Angeles, CA. Address reprint requests to: Wendy Mack, Ph.D., University of South- ern California, Department of Preventive Medicine, 1540 Alcazar St., CHP-218, Los Angeles, CA 90089. Received November 27, 2000; revised July 27, 2001; accepted August 13, 2001.