Among Chinese women, breastfeeding appears to cut the risk of rheumatoid arthritis by 50 percent.

During the winter chill, creaking joints and stiffness plague the 1 to 2 million Americans living with rheumatoid arthritis (RA).

RA onset typically occurs between the ages of 40 and 60, and is more common in women. The chronic condition is an autoimmune disease characterized by swelling and inflammation around one or more joints.

Though there is no cure, researchers at the University of Birmingham in the U.K. have found a surprising correlation: breastfeeding, especially for a longer period of time, may cut a woman’s risk of RA in half. The researchers found no association between oral contraceptive use and the risk of RA.

It seems Pope Francis was on the mark in supporting breastfeeding whenever necessary. Many doctors already agree about the benefits of breastfeeding for the nutrition and future mental and physical health of the infant.

There are many good reasons to promote breastfeeding, and this research suggests that risk reduction for rheumatoid arthritis may be another one,” says study co-author Elizabeth Rankin, Ph.D., a rheumatology consultant at the university.

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Hormonal and reproductive factors have already been implicated in RA, the study reports. But most RA studies have involved women from the U.S. and Scandinavia.

“The interest is that this finding has been reproduced in another relatively understudied population…middle aged and elderly Chinese women,” Rankin says.

The replication of these findings with a different population, “strengthens the likelihood that the previously reported associations are real, and not a chance finding,” says study co-author Peymane Adab, M.D., a professor of public health at the University of Birmingham.

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Data from more than 7,000 women 50 years of age or older in the Guangzhou Biobank Cohort in China was collected using questionnaires. Subjects reported their breastfeeding habits, oral contraceptive use, and RA status.

What researchers found was striking: compared with those who never breastfed, breastfeeding—especially for at least 36 months—was associated with a 50 percent drop in the risk of RA.

Definitions of RA can vary, so researchers limited their definition to noticeable pain and swelling in at least three small joints.

This study supports the theory that RA incidence is tied to hormonal changes, but more research is needed, including longitudinal studies that follow women from childbirth to RA onset, says Adab.

“Also, clinical studies that examine the biological mechanism—how breastfeeding may be affecting hormonal, immune-based, or other pathways to protect against RA in future,” she adds.

Adab, Rankin, and their fellow researchers proposed some mechanisms that tie breastfeeding to a reduced risk of RA, but at the moment they are just hypotheses. One reason may be an extension of the well-known anti-inflammatory effects of pregnancy-related hormones. Progesterone, an anti-inflammatory hormone, is found in high levels in the body during pregnancy and remains high during breastfeeding.

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Another hypothesis, following a 2007 study published in Environmental Health Perspectives, is that through prolonged breastfeeding, mothers are able to reduce the burden of organic pollutants that can increase the risk of RA.

These findings should help convince women who have yet to make a decision about breastfeeding that forgoing the formula may benefit more than just their infants.