May 13 (HealthDay News) -- Women who breast feed for more than one year reduce their risk of rheumatoid arthritis (RA) by half, according to a new Swedish study.

The researchers also found that having children but not breast-feeding offered women no protection against the disease.

Taking oral contraceptives also failed to reduce the risk of RA. It's been suspected that oral contraceptives offer protection against the disease because they contain hormones that are elevated during pregnancy.

The Malmo University Hospital study included 136 women with rheumatoid arthritis and 544 women without the disease. Women who breast-fed for 13 months or more were half as likely to get RA as those who never breast-fed. Women who had breast-fed for one to 12 months were 25 percent less likely to get the disease than those who never breast-fed.

Over the past 30 years, the number of women breast-feeding for more than six months has increased dramatically, the researchers noted. They said it's difficult to say whether there's a link between higher rates of breast-feeding and a corresponding decline in the number of women with rheumatoid arthritis.

However, the results of this study offer yet another reason why women should breast-feed their babies, the researchers concluded.

The study findings were published online May 13 in the Annals of the Rheumatic Diseases.

Rheumatoid arthritis is a chronic disease, characterized by inflammation of the lining -- or synovium -- of the joints. It can lead to long-term joint damage, resulting in chronic pain, loss of function and disability, according to the Arthritis Association.

SOURCE: BMJ Specialist Journals, news release, May 13, 2008