Researchers believe breastfeeding protects women against the condition as it makes them temporarily stop getting periods, which reduces their lifetime exposure to the hormone estrogen.
High estrogen levels have previously been linked to developing breast cancer.
Breastfeeding may also help to remove cells with damaged DNA that could otherwise lead to tumor development.
Five months of breastfeeding lowers cancer risk by 2%
Researchers from the American Institute for Cancer Research (AICR) and the World Cancer Research Fund analyzed 18 studies that examined breastfeeding.
Of these, 13 investigated the effects of the length of time spent lactating.
Results reveal that for every five months a woman breastfeeds, her risk of breast cancer is reduced by two percent.
The report also found that carrying excess weight after menopause increases a woman's risk of developing the condition, yet it is protective while women are still able to conceive.
For both pre- and postmenopausal women, alcohol increases their risk of breast cancer and exercise reduces it, the report adds.
Babies who are breastfed are also less likely to gain weight in later life, the study found.
Study author Alice Bender from the AICR, said: 'It isn't always possible for moms to breastfeed but for those who can, know that breastfeeding can offer cancer protection for both the mother and the child.'
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