Women who breastfeed for more than a year reduce their risk of rheumatoid arthritis by around a half, a Swedish study has found.

Researchers from Sweden's Malmo University Hospital compared 136 women with rheumatoid arthritis to 544 women of a similar age without the disease.

They found that that those who had breastfed for 13 months or more were half as likely to get rheumatoid arthritis as those who had never breastfed.

Those who had breastfed for one to 12 months were 25 per cent less likely to develop the condition.

The study found that taking oral contraceptives, which are suspected to protect against the disease because they contain hormones that are raised in pregnancy, did not seem to protect the women against developing rheumatoid arthritis.

It also revealed that simply having children and not breastfeeding did not seem to be protective either.

According to the study, which is published in the Annals of Rheumatic Diseases, the proportion of women breast feeding for more than six months has increased dramatically over the past 30 years.

The researchers concluded that it was difficult to say whether there was a connection between higher rates of breastfeeding and a corresponding fall in the number of women affected by rheumatoid arthritis, but that the results provided yet another reason why women should continue breastfeeding.

About 400,000 people in Britain have rheumatoid arthritis.