Women who breastfeed for over 6 months are less likely to develop early breast cancer than women who do not breastfeed - as long as they do not smoke - a nurse-led study suggests.
Emilio Gonzalez-Jimenez PhD, of the University of Granada in Spain, and his colleagues drew from the medical records of 504 women (between 19 and 91 years of age) who had been treated for breast cancer at one of the city's hospitals.
Women who had not breastfed their babies were, on average, found to get breast cancer 10 years earlier than breastfeeding mothers.
The university team included a number of factors in their analysis - age of breast cancer diagnosis, length of breastfeeding, family history of cancer, obesity, alcohol consumption and smoking habits.
"Regardless of the patients' family history of cancer," the researchers said, breastfeeding meant that mothers who were going to develop the disease were going to do so at a later age.
The nursing experts warn, however, that smoking countered the benefits of breastfeeding:
"In contrast, female smokers were diagnosed with breast cancer at a younger age and obtained no significant benefit from a longer period of breastfeeding."
In the authors' study paper background, they cite estimates of 720,000 cases of breast cancer a year worldwide - "20% of all cancers." They note that 17-36% of all breast cancers are in women under 40.
Dr. Emilio Gonzalez-Jimenez and his team explain that "there are various explanations why breastfeeding seems to prevent breast cancer and why it appears to significantly benefit female health."
Among the biological theories to explain breastfeeding benefit, the authors say:
"The most probable of these are the hormonal changes that take place during pregnancy and lactation."
Gain in life-expectancy
The results of the study showed a gain in years lived for breast cancer patients who breastfed their babies "for periods of longer than 6 months," the authors conclude.
"In fact," they say, "our study showed an average gain of 10 years in the mean age at diagnosis."
The study ends with this conclusion:
"Breastfeeding for periods of over 6 months not only provides children with numerous health benefits, but also protects the mother from serious diseases such as breast cancer.Breastfeeding is a potential ally in the fight against breast tumors."
The researchers call for continued analysis and study of the benefits of breastfeeding.
In other recent news, breastfeeding for longer has been linked to higher IQ in offspring.
The CDC (Centers for Disease Control and Prevention) has statistics showing that breastfeeding went up in the past decade. The proportion of babies being breastfed rose 6%, from 71% in 2000 to 77% in 2010.