Use of thyroid supplements in relation to the risk of breast cancer
S. Shapiro, D. Slone, D. W. Kaufman, L. Rosenberg, O. S. Miettinen, P. D. Stolley, R. C. Knapp, T. Leavitt Jr, W. G. Watring, N. B. Rosenshein and D. Schottenfeld
We conducted a case-control study to determine whether the use of thyroid
supplements increases the risk of breast cancer. We compared 659 women with
breast cancer and 1,719 control subjects. The rates of use of thyroid
supplements were 9.1% and 8.7%, respectively (age-standardized rate ratio,
1.0; 95% confidence interval, 0.7 to 1.3). There was no evidence of an
association when women known to be at increased risk for breast cancer (eg,
nulliparae) were examined, even when thyroid supplements were taken for
more than 15 years. Overall, there were no grounds to suggest that the
long-term use of thyroid supplements increases the risk of breast cancer.
