LLLI Center for Breastfeeding Information

Journal Abstract and Review of the Month for February 2006

"Lactation and risk of endometrial cancer in Japan: a case-control study"

Authors: Chikako Okamura, et al.

Tohoku J Exp Med 2006 Feb; 208(2):109-15.

Abstract:

The incidence of endometrial cancer among Japanese women has historically been much lower than that of Western women, so the recent rise in diagnoses has been of much concern. Speculation about the cause of this increase has centered around the changes in diet and lifestyle of modern Japanese women whose traditional ways have been impacted by globalization and their subsequent exposure to the same risk factors faced by Western women. However, even in this more intermingled context, Japanese women still have significantly different types of exposure to risk factors. For example, Japanese women are far less likely than their Western counterparts to take either oral contraceptives during their child-bearing years or hormone-replacement therapy during menopause. These facts alone make the extrapolation of studies done in Western countries difficult to apply in Japan.

A fresh study was therefore undertaken to consider the possible causes and potential preventors of endometrial cancer in Japanese women. Number of pregnancies and deliveries; age at menarche and menopause; age at first and last pregnancy; body mass index; personal histories of cancer, hypertension, and diabetes; oral contraception use; and breastfeeding history were all considered. Both pregnancy and oral contraception use were found to have a significant protective effect. Additionally, Japanese women who had breastfed were less likely than their counterparts who had not breastfed to get endometrial cancer. The protective effect decreased the farther away the women got from weaning. Neither frequency nor duration of breastfeeding appeared to have a significant affect on cancer risk. This refuted several earlier studies from Japan, but supported more recent ones from the West.

The authors theorize that there has been a substantial decline in both the number of births and prevalence of breastfeeding in Japan and that this may account for the spike in endometrial cancers. The suppression of estrogen that occurs with lactation reduces blood levels of that hormone. This suppression is mimicked in oral contraception users through the oppositional force of progesterone. In both situations, the amount of time that the endometrium is exposed to estrogen is reduced, which may account for the lessened endometrial cancer risk of both oral contraceptive users and women who have breastfed.

This paper is categorized by the following keywords:

Cancer
Estrogen
Contraception
Cultural Influences
Women

The full text of this article is available (for free) at: http://www.jstage.jst.go.jp/article/tjem/208/2/109/_pdf

A comprehensive list of benefits to mothers and infants from breastfeeding can be found at:
http://www.lalecheleague.org/docs/OutcomesApril2006.pdf

LLLI Media Releases
http://www.lalecheleague.org/advocacy/WHAstatement05.html
58th World Health Assembly Statement by La Leche League International
http://www.lalecheleague.org/Release/worldhealth.html