Add this to the list of benefits to breast-feeding: women who do it for 13 months or longer are 50 percent less likely to develop rheumatoid arthritis than women who do not, according to a study published Tuesday in the Annals of the Rheumatic Diseases.

The study looked at 136 women with the disease and 544 women without the disease, all within the same age range. Researchers discovered that the women who had breast-fed for longer periods of time were much less likely to develop the condition.

Women who breast-fed their babies for one to 12 months were 25 percent less likely to develop rheumatoid arthritis.

However, oral contraceptives, which were once suspected of protecting against rheumatoid arthritis because of the hormones they contain, did not ward off the disease, the study found.