Breast-feeding is known to have multiple health benefits for the baby and may protect mothers against breast cancer and ovarian cancer. Now a group of Swedish scientist discovered that it could also protect women from rheumatoid arthritis (RA).

According to their findings published in the Annals of Rheumatic Diseases, women who had breast fed for 13 months or more had a significantly reduced risk of developing RA.

The researchers compared 136 women with rheumatoid arthritis with 544 women of a similar age without the disease. They found that that those who had breast fed for longer were much less likely to get rheumatoid arthritis.

Possible explanations for the protective effect of breast feeding include long-term immunomodulation, such as the development of progesterone receptors on lymphocytes, dysregulated hypothalamic–pituitary–adrenal axis, and differences in cortisol concentrations.

The study also found that taking oral contraceptives, which are suspected to protect against the disease because they contain hormones that are raised in pregnancy, did not have the same effect. Also, simply having children and not breast feeding also did not seem to be protective.

“Although it is difficult to separate the effect of breast feeding from that of childbirth, our data suggest that RA is inversely associated with long-term breast feeding, rather than with the number of children born,” the authors concluded.

Overall, women have more than a twofold higher incidence of RA than men. This is mainly due to an increased risk in women during their reproductive years, when the incidence shows a female/male ratio of 5:1.