Women who breastfed for 13 months or more were 54 per cent less likely to develop the condition than women who had never breastfed.
Taking oral contraceptives, which were suspected to help protect against RA because they contain hormones that are raised in pregnancy, failed to offer any protection.
The findings coincide with a DoH campaign to encourage more mothers to breastfeed.
What is the research?
The study compared 136 women aged 44-74 who developed RA between 1991 and 1996 with a control group of 544 healthy women. They completed a questionnaire on oral contraceptive use and if they had breastfed at all.
After adjusting for other risk factors such as smoking, women who had breastfed for 13 months or more were found to be 54 per cent less likely to develop RA than women who had never breastfed.
Women who breastfed for up to 12 months were 25 per cent less likely to have RA than wo- men who had never breastfed.
Thirty-two per cent of women with RA reported that they had never breastfed, compared with 25 per cent in the control group. Just under half of the women were found to have used oral contraceptives. These failed to lower the risk of RA.
What do the researchers say?
Lead researcher Dr Mitra Pikwer, from the department of rheumatology at the University of Malmo in Sweden, said: 'The exact mechanism linking breastfeeding to a lower risk of RA is unknown but it may be due to hormonal changes.'
Researchers propose that breastfeeding lowers RA risk by increasing the levels of oxytoxin, which is known to reduce cortisol concentrations, induce well-being and lower BP.
What do other researchers say?
Professor Alan Silman, medical director at the charity Arthritis Research Campaign, said that findings went against previous research which suggested that breastfeeding was a risk factor for developing RA in women soon after giving birth to their first child.
'This study is different in that it looks at longer-term risk. One explanation could be that women who breastfeed may lead healthier lifestyles,' he said.
- Women who breastfeed for more than a year could halve their risk of developing RA.
- Taking oral contraceptives did not reduce the risk of RA.
- Further studies required to identify how breastfeeding lowers RA risk.