Reproductive Choices and Breast Cancer Risk: A HealthCentral Explainer

SSuchy Editor
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    There’s been a small, steady and troubling increase in breast cancer rates among a specific demographic of women for the last 37 years. A study published in the Journal of the American Medical Association uncovered, to the surprise of many breast cancer experts, that the number of young women – women between 25 and 39 years old – developing advanced breast cancer has increased by 2 percent every year since 1976.


    That increase translates to about 1.4 additional breast cancer cases per 100,000 people every year for 34 years. They are small numbers at first glance, but over time they add up. Plus, the steady rise in cases shows no sign of ending, meaning more young women will be at risk every year.

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    The trouble with young women


    Any increase in cancer cases is disturbing, but what’s especially troubling about these cases is the age at which they strike.


    Young women are not regularly screened for breast cancer the way older women are. So, if cancer does develop in a young woman, it is far more likely to have spread to other areas of the body (metastasized) before it is discovered. This leaves women with fewer treatment options and less time to treat the cancer. Consequently, the prognosis for most young women who are diagnosed with breast cancer is only about five years.


    Why this age?


    That is the question that seems to puzzle most of the researchers. Why the steady increase in advanced breast cancer among this particular subset of women, but no corresponding increase in any other demographic?


    Several theories have emerged, but it is helpful first to understand the connection between breast cancer risk and hormone exposure.


    More hormones, more cancer risk


    Several studies indicate that a woman’s risk of developing breast cancer at some point during her life is related to her exposure to certain hormones produced by her ovaries.


    These hormones – estrogen and progesterone – stimulate cell growth in the body, even for cells that you don’t want in your body, such as cancerous cells.


    So, anything that increases and sustains the presence of these hormones can increase her risk of developing breast cancer, which is likely to be particularly aggressive. 


    According to the National Cancer Institute, some of the reproductive factors that prolong hormone exposure include:


    • Early onset of menstruation
    • Late onset of menopause
    • Later age of first pregnancy
    • Never giving birth


    Delayed childbirth


    With the connection between hormone exposure and cancer risk in mind, let’s turn to a 2009 Centers for Disease Control and Prevention (CDC) report on the later age of a woman’s first pregnancy. According to the study, between 1970 and 2006, the average age of first-time mothers increased from 21.4 to 25 years old. The increase was seen in varying degrees across all states and all demographics.


    The National Cancer Institute (NCI) reports that pregnancy and breastfeeding can both protect against breast cancer. First, childbirth reduces the lifetime number of menstrual cycles a woman will have, which in turn reduces her exposure to the hormones that stimulate cell growth.


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    Second, breastfeeding causes breast cells to mature so that they can produce milk. These cells are more resistant to being transformed into cancerous cells than cells that have not matured. 


    So, the NCI concludes that women who give birth to their first child early, have several children and breastfeed for at least a year, cut their risk of developing breast cancer by about 50 percent.


    Rise of hormonal contraceptive use


    Another factor to consider is the rising popularity of estrogen and progesterone hormonal contraceptives.


    The Food and Drug Administration approved the birth control pill for contraceptive use in 1960. By 1962, 1.2 million American women were on The Pill and by 1965 the number grew to 6.5 million. Today, over 10 million women across the country use a hormonal contraceptive, which is the most popular form of contraception among white women, women in their teens and 20s, cohabitating women, childless women and college graduates.


    According to the NCI and the CDC, prolonged exposure to hormones such as progesterone and estrogen are linked to a higher risk of breast cancer. And the NCI has found that women, particularly young women, who use hormonal contraceptives have an elevated risk of breast cancer. This increased risk does not decrease to normal until 10 years after a woman goes off The Pill.


    Putting it together


    We know that numerous studies across several decades suggest that early and frequent childbirth has a protective effect against breast cancer. We also know that the average age of a woman’s first pregnancy in the U.S. has increased, along with the number of women using hormonal contraceptives.


    Both of these trends began to emerge in the 1960s and 1970s, which is when the rate of aggressive breast cancer among young women began its steady rise. It could be that women who delay childbirth and use hormonal contraception to do so unknowingly increase their risk of breast cancer. 


    As always, more research is needed to determine this link. But women need to be aware of the factors that raise their risk of breast cancer at a young age.





    Journal of the American Medical Association, Incidence of Breast Cancer with Distant Involvement Among Women in the United States, 1976 to 2009 (February, 2013).


    National Cancer Institute, Reproductive History and Breast Cancer Risk (May, 2011).


    Centers for Disease Control and Prevention. Delayed Childbearing: More Women Are Having Their First Child Later in Life (August, 2009).


    Nikolchev, Alexandra,, A brief history of the birth control pill (May, 2010).


    The Guttmacher Institute, Contraceptive Use in the United States


Published On: March 11, 2013