Comparable use of oral contraceptives or hormone replacement therapy showed no significant effect on the risk of developing rheumatoid arthritis, said Dr. Mitra Keshavarz, of Malmo Hospital University, Sweden.

The findings add to the "growing body of evidence in favor of breastfeeding and its positive health implications -- this time demonstrating its protective benefits for the mother," Keshavarz said.

The study compared information from the Swedish National Hospital Discharge and the National Cause of Death Register from 1991 to 1996.

The findings were presented at the Annual European Congress of Rheumatology in Barcelona.