Women who breast-feed their babies longer are less likely to get rheumatoid arthritis, Swedish researchers said on Tuesday.
Mothers who breast-fed for 13 months or more were half as likely to get the painful joint condition as women who never breast-fed, said Mitra Pikwer and colleagues at the Malmo University Hospital in Sweden, who led the study.
"Although it is difficult to separate the effect of breast-feeding from that of childbirth, our data suggest that rheumatoid arthritis is inversely associated with long-term breast-feeding, rather than with the number of children born," they said.
The researchers said they wanted to see if a larger, community-based study would echo earlier studies on the links between breast-feeding or the use of oral contraceptives and the condition affecting about 20 million people worldwide.
Rheumatoid arthritis is an autoimmune disease caused when the body confuses healthy tissues for foreign substances and attacks itself.
Some drugs to treat the condition seek to reduce inflammation directly while others tone down the immune system's response, which can leave some patients vulnerable to infections and cancer.
The Swedish team compared 136 women with rheumatoid arthritis and 544 women of similar age without the disease. They also found that breast-feeding for between up to 12 months made women 25 percent less likely to get the joint condition.
The findings bolster previous research linking breast-feeding to a reduced risk of the disease. But, as with other studies, the Swedish teams said they did not know the exact reason why.
Breast-feeding is known to provide multiple benefits for the baby and studies have shown the practice may also protect mothers from breast and ovarian cancers.
The study published in the British Medical Journal's Annals of the Rheumatic Diseases also suggested that oral contraceptives — thought to offer protection because they contain certain hormones — did not seem to make a difference.