Background: Selenium is an essential trace element that is important for thyroid hormone metabolism and has antioxidant properties which protect the thyroid gland from oxidative stress. The association of selenium, as well as intake of other micronutrients, with thyroid cancer is unclear.
Methods: We evaluated associations of dietary selenium, beta-carotene, calcium, vitamin D, vitamin C, vitamin E, folate, magnesium, and zinc intake with thyroid cancer risk in the National Institutes of Health - American Association of Retired Persons Diet and Health Study, a large prospective cohort of 566,398 men and women aged 50-71 years in 1995-1996. Multivariable-adjusted Cox proportional hazards regression was used to examine associations between dietary intake of micronutrients, assessed using a food frequency questionnaire, and thyroid cancer cases, ascertained by linkage to state cancer registries and the National Death Index.
Results: With the exception of vitamin C, which was associated with an increased risk of thyroid cancer (HR(Q5 vs Q1), 1.34; 95% CI, 1.02-1.76; P(trend), <0.01), we observed no evidence of an association between quintile of selenium (HR(Q5 vs Q1), 1.23; 95% CI, 0.92-1.65; P(trend), 0.26) or other micronutrient intake and thyroid cancer.
Conclusion: Our study does not suggest strong evidence for an association between dietary intake of selenium or other micronutrients and thyroid cancer risk. More studies are needed to clarify the role of selenium and other micronutrients in thyroid carcinogenesis.