Mothers who breast feed their babies for longer periods are likely to have a reduced risk of developing rheumatoid arthritis (RA), a chronic disorder that causes inflammation of the joints and surrounding tissues, a new study suggests.

While previous studies have suggested that hormonal factors play a part in the development of RA, the new study found that breast feeding for 13 or more months was associated with a reduced risk of developing RA compared to women who had never breast fed.

The longer the breast feeding period, the lower the mother's risk of developing RA in later life, according to the new data presented at EULAR 2007, the Annual European Congress of Rheumatology in Barcelona, Spain.

The latest study was conducted using the data from a community-based health study in Spain between 1991 and 1996, comparing health information from 136 women, reported health portal Medical News Today .

Comparable use of oral contraceptives (OCs) or hormone replacement therapy (HRT) did not show a significant effect on the risk of developing RA, it said.

"This study specifically highlights the potential of naturally-induced hormones in protecting individuals from developing RA in the future," said lead researcher Mitra Keshavarz, of Malmo Hospital University, Sweden.

"It further adds to the growing body of evidence in favour of breast feeding and its positive health implications this time demonstrating its protective benefits for the mother," he added.

Studies in the past have shown that breast milk is perfectly suited to nourish infants and protect them from illness. Breast-fed infants have lower rates of hospital admissions, ear infections, diarrhoea, rashes, allergies and other medical problems than bottle-fed babies.

Breast-feeding not only helps the child against various diseases but benefits the mother as well. Previous studies have shown that it can lower a mother's risk of getting cancer.