Reproductive Factors and Risk of Thyroid Cancer in Women

Background: The incidence of thyroid cancer in women is increasing at an alarming rate, with greatest risk in the reproductive years. Establishing relationships of hormonally related reproductive factors with thyroid cancer has been difficult. We aimed to elucidate potential risk factors for thyroid cancer in a large cohort of women. Methods: Among 116,228 women in the Nurses’ Health Study II followed from 1989 to 2013, 620 cases of thyroid cancer were identified. We examined reproductive and hormone-related factors, including age at menarche, age at menopause, parity, oral contraceptive use, and postmenopausal hormone therapy use. Pregnancy, reproductive years, and months of breastfeeding were used as surrogate markers for exposure to endogenous reproductive hormones. We used multivariable Cox models to calculate relative risks and 95% confidence intervals for the associations between these factors and risk of thyroid cancer. Results: Number of reproductive years of 41 years or more was associated with more than double the risk of thyroid cancer compared with 30 years or fewer (relative risk, 2.20; 95% confidence interval, 1.19–4.06). The other variables analyzed (parity number, months of breastfeeding, age at menarche, menopausal status, and postmenopausal hormone therapy) were not associated with the risk of thyroid cancer. Women who entered menopause at age 45 years or older had a higher risk of thyroid cancer compared with women who entered menopause at a younger age. This result did not reach statistical significance; however, there was a linear trend between later age at menopause and increased risk of thyroid cancer (ptrend = .009). Conclusions: This study used a unique large, longitudinal dataset to assess thyroid cancer risk factors and potential confounders over an extended time frame. Our key finding suggests increased risk of thyroid cancer may be associated with a variety of indicators of longer reproductive years. The Nurses’ Health Study II has provided new insights into the hormonal risks associated with thyroid cancer.


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Work Title Reproductive Factors and Risk of Thyroid Cancer in Women
Subtitle An Analysis in the Nurses’ Health Study II
Open Access
  1. Jane R. Schubart
  2. A. Heather Eliassen
  3. Amber Schilling
  4. David Goldenberg
License In Copyright (Rights Reserved)
Work Type Article
  1. Women's Health Issues
Publication Date January 1, 2021
Publisher Identifier (DOI)
Deposited July 19, 2021




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Version 1

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  • Added WHI_6757.pdf
  • Added Creator Jane R. Schubart
  • Added Creator A. Heather Eliassen
  • Added Creator Amber Schilling
  • Added Creator David Goldenberg
  • Published
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