This study was undertaken to determine the relationship between thyroid supplements and breast cancer. The incidence of breast cancer among the patients who received thyroid supplements was 12.13%, while in the control group it was 6.2%. The incidence rate of breast cancer was 10%, 9.42%, and 19.48% among patients who received thyroid supplements for one to five, 5 to 15, and for more than 15 years, respectively. The incidence of breast cancer among nulliparous women who received thyroid supplements was 33%, while in the nulliparous women without thyroid supplements the incidence was only 9.25%. Even in a specific age group, the incidence rate of breast cancer was higher among patients receiving thyroid supplements, when compared to the control patients in the same age group.
(JAMA 236:1124-1127, 1976)
Kapdi CC, Wolfe JN. Breast CancerRelationship to Thyroid Supplements for Hypothyroidism. JAMA. 1976;236(10):1124–1127. doi:10.1001/jama.1976.03270110022020