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Home Prevention Can breastfeeding reduce your risk of developing breast cancer?

Can breastfeeding reduce your risk of developing breast cancer?

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Interestingly, new research conducted over the past decade suggests yes, breastfeeding is linked to lower cases of breast cancer. Many risk factors have been established relating to women developing breast cancer, of which women have little or no control over, such as female gender, weight gain after 18 years of age, obesity, physically inactive lifestyles, higher breast density, long menstrual history (menstrual periods that start early and/or end later in life), certain gene mutations, having a first degree relative with breast cancer and most importantly increasing age1. Consequently, scientists are exploring areas in which women can actively prevent breast cancer by decreasing their personal risk, including reducing alcohol consumption, maintaining a healthy body weight1, increasing physical activity2, quitting smoking3 and as scientists have now noticed, the possible protective benefits of increased breastfeeding4. An analysis of 47 studies examining the effects of breastfeeding, among other aspects of child bearing, encompassing 30 countries and roughly 145 000 women demonstrated that breast feeding for 12 months conferred a 4.3% decrease in risk of developing breast cancer4. This comprehensive meta analysis, founded by the Collaborative Group on Hormonal Factors in Breast Cancer* took into consideration participantʼs age, race, country of origin, socio-economical distribution, number of children, age at time of first childʼs birth, menopausal status and whether or not women breastfed, and if so, the duration of breastfeeding. The researchers followed 50 302 women with breast cancer and 96 973 without. They then examined what was different between the 2 groups of women. What they discovered was astounding, no matter race, country of origin or social status, on average, the group of women without breast cancer had more children, had children at a younger age and had breast fed for longer when compared to the group of women who had developed breast cancer3. Even when women from both groups had the same number of children, those who had never breastfed were at higher risk of developing breast cancer4.



Breast cancer is the most commonly diagnosed cancer among women (excluding skin cancers which are usually benign) and is the 2nd leading cause of death in women after lung cancer5. By the end of December 2013 it is estimated that approximately 232 340 women will have been newly diagnosed with invasive breast cancer in the US and of those women roughly 39 620 will die1. With the advent of better screening techniques and progress in current pharmaceutical treatment regimes, breast cancer incidence has decreased from 2005 to 2009, about 3.0% per year in women younger than 50 and 2.0% per year in women 50 and older1. Despite this decline, women have a 1 in 202 likelihood of developing breast cancer by the age of 39 and a 1 in 8 lifetime risk1. The average age at diagnosis was 50.1 years old in the worldwide female populations studied4. Though the development of breast cancer is hypothesized to be multi-factorial, our inherited genetics, environmental factors and other reproductive factors, such as menstrual cycle history or age at onset of menopause are out of our control. So what can women do to reduce their lifetime risk of developing breast cancer? One way, as cited in the aforementioned analysis, includes the protective effects of breast feeding and child bearing, which will be discussed further.


Does the duration of breastfeeding influence breast cancer incidence?

The results observed by the Collaborative Group on Hormonal Factors in Breast Cancer showed the relative risk of breast cancer is reduced by 4.3% for each year that a woman breastfeeds4. Though breastfeeding for any duration seemed to positively influence breast cancer rates in the women participating in this study, the most prominent decrease in risk was associated with breastfeeding for at least 12 months. The longer women breastfeed the more they are protected against breast cancer, this helps explain the higher breast cancer prevalence in developed countries such as the United States, where women breastfeed for shorter durations or not at all. In this analysis, which comprised 80% of available data at the time on the subject, the proportion of women with children who breastfed was the lowest in the USA, at around 50%6 whereas in Japan, Scandinavia and most developing countries more than 90% of female participants had breastfed4. The lifetime duration of breastfeeding was much shorter for women in developed countries than developing countries (8.7 months vs 29.2 months respectively)4. Overall, women participants who developed breast cancer had breastfed, on average, for 9.8 months compared to the 15.6 months of breastfeeding on average displayed by females without breast cancer4.


Does the number of child births effect breast cancer rates?

The protective effects of childbearing have long been established7 as increased parity (the number of children you have) reduces the risk of breast cancer significantly. Researchers have observed a 7.0% decrease in relative risk of developing breast cancer for each birth4. Women participants without breast cancer had on average 2.6 children compared to the 2.2 child births on average displayed by the women who developed breast cancer8. Like breast feeding, increased parity confers a cumulative risk reduction regarding breast cancer development. This risk reduction is amplified by having more children and breastfeeding longer. Fewer parous women with cancer had ever breast fed compared to parous women without breast cancer (71% vs 79%)4. When examining both groups of participants who had the same number of children, a greater number of women with breast cancer had never breastfed. This suggests that having children provided some protection against breast cancer but the more child births in the presence of breastfeeding correlated with an increased protection. In parous women who breastfed, the greatest risk reduction was seen with longer durations of breastfeeding. The following graph compares parity (number of children), breastfeeding habits and risk of developing breast cancer4. It shows that parous women who never breastfed (the black boxes) were at a greater risk of breast cancer than their breastfeeding counterparts (white boxes). Also illustrated is the decreased risk of breast cancer with increased number of births; the women participants without breast cancer, on average had more children and breastfed longer.


4Table 1

Table 1



Does having children earlier protect against breast cancer?

These studies revealed that the earlier the better9. For each year younger that women were when they had their first child conferred a 3.0% lifetime risk reduction4. On average, female participants without cancer were younger than the women who developed breast cancer at the time of their first child birth. Table 2 displays the differences between the number of women with breast cancer and controls (women without breast cancer) in regards to the duration of breastfeeding, the number of children breastfed and the women’s age at first birth.  The results suggest women had the lowest rates of developing breast cancer if they breastfed longer, had more children and started having children at a younger age4.


Tabe 2




How does breastfeeding and increased parity protect against breast cancer?

Though the exact reason behind breastfeedingʼs protective nature in regards to breast cancer development has not been elucidated, many scientists believe the risk reduction is provided by decreased lifetime estrogen exposure10. Estrogen is a chemical produced mainly by the ovaries in premenopausal women and the duration of exposure to estrogen seems to be closely related to breast cancer risk: a 1-year delay in the onset of menarche (first menstruation) is associated with a 5% reduction in lifetime risk for developing breast cancer11, and each 1-year delay in the onset of menopause is associated with a 3% increase in risk4. As with increased number of pregnancies, breast feeding decreases female exposure to estrogen by inhibiting menstrual cycles. It is also been shown that during menstruation, specific hormones, particularly estrogens, cause changes in female breast tissue cells (these changes can manifest as breast tenderness or enlargement) and possible abnormal changes during these periods could ultimately participate in breast cancer development. Consequently reducing the number of cyclical changes to breast tissue would decrease the chance for random genetic errors during cell proliferation and could reduce the risk of breast cancer development12. This also could explain why women who have extended menstrual histories (early age of first menstruation and/or late onset of menopause) have an increased risk of breast cancer as they have longer lifetime exposure to these cellular changes and hormonal effects13.



The results discussed are impressive and could have a tremendous impact on breast cancer incidence world wide as the factors examined proved beneficial to all women regardless of race, geographic location or annual income. Though a 4.3% risk reduction in developing breast cancer by breast feeding for 12 months seems marginal or inconsequential, that figure would represent nearly 10 000 american women this year alone who would be saved a diagnosis of breast cancer. In developed countries like the USA, it is estimated that breastfeeding habits could contribute to a cumulative reduction of breast cancer by more than half, from 6.3 to 2.7 per 100 women by age 70, if they breastfed for at least 12 months and had the same number of pregnancies as seen in women of developing countries4. Breast cancer is a disease of uncertainty, where known modifiable risk factors are scarce, consequently, discovery of new preventative measures is of paramount importance. In developed nations like the USA, where cultural, social and economic considerations influence breastfeeding practice and duration, as well as family size, this analysis shows that increased parity at a younger age coupled with subsequent prolonged breastfeeding could prove monumental in disease prevention and could decrease breast cancer incidence drastically.




Brian Gaffney

Medical student at the University of St. Eustatius School of Medicine, St. Maarten,

Netherlands Antilles





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* Members of the Collaborative Group on Hormonal Factors in Breast Cancer include Analysis and writing committee—V Beral, D Bull, R Doll, R Peto, G Reeves. Steering Committee—D Skegg (chairman), G Colditz, B Hulka, C La Vecchia, C Magnusson, T Miller, B Peterson, M Pike, D Thomas, F van Leeuwen.