(This study did not assess risk of thyroid cancer in women who were breastfed as infants)
Abstract:
Clin Nutr. 2016 Oct;35(5):1039-46. doi: 10.1016/j.clnu.2015.12.005. Epub 2015 Dec 17.Breastfeeding and thyroid cancer risk in women: A dose-response meta-analysis of epidemiological studies.
Yi X1, Zhu J2, Zhu X3, Liu GJ4, Wu L5.
Author information
Abstract
BACKGROUND & AIMS:
The association between breastfeeding and thyroid cancer risk is not consistent from epidemiological studies. To better clarify the association including assessing a potential dose-response relationship, we conducted a comprehensive meta-analysis.
METHODS:
We searched PubMed (MEDLINE) up to November 2015 for prospective studies or case-control studies that evaluated the association between breastfeeding and risk of thyroid cancer. Effect estimates were pooled using a fixed-effects model.
RESULTS:
Nine reports (2 prospective studies, 6 case-control studies and 1 pooled analysis of 14 case-control studies) involving 2423 cases and 350,081 non-cases were identified. After pooling relevant studies, there was a significant inverse association between ever breastfeeding and risk of thyroid cancer (RR = 0.91, 95% CI 0.83-0.99), with minor heterogeneity (I(2) = 10.1%). The dose-response analysis revealed a significant linear relationship between the duration of breastfeeding and risk of thyroid cancer. The summary RR for an increment of 1 month of breastfeeding with risk of thyroid cancer was 0.983 (95% CI 0.98-0.99). When focusing on cohort studies, a more prominent linear dose-response relationship was detected, with the combined RR for every increment of 1 month of breastfeeding to be 0.965 (95% CI 0.96-0.97).
CONCLUSIONS:
This meta-analysis suggests that breastfeeding is potentially inversely associated with thyroid cancer risk. Also longer duration of breastfeeding may further decrease thyroid cancer risk. If validated in large-scale prospective studies, our findings may have implications for impacting women's decision in breastfeeding.
Copyright © 2015 Elsevier Ltd and European Society for Clinical Nutrition and Metabolism. All rights reserved.
The current study reviewed the available studies on thyroid cancer and breastfeeding. Based on this knowledge, we can say that there is an association between breastfeeding and a decreased risk of thyroid cancer, but we don’t know cause and effect. In other words, the association could be due to something else that breastfeeding women do, such as eating more vegetables or exercising more, as opposed to the physiologic effects of breastfeeding itself.
IABLE Comment by Anne Eglash MD, IBCLC, FABM
There is so much more to learn about this topic. Just like breast cancer, there are genetic risks for thyroid cancer, and we don’t know the effect of breastfeeding for a woman who falls into a higher risk category.
However, I think based on this study, we can share this information when counseling women on risks of not breastfeeding, by explaining that thyroid cancer risk might be reduced if she breastfeeds, and her risk might be lowered even more the longer she breastfeeds.
