Rheumatoid arthritis (RA) is an autoimmune disease where the immune system starts attacking the body’s own tissues, causing inflammation.
Common symptoms include painful, swollen joints, stiffness and fatigue.
Rheumatoid arthritis affects around 400,000 people in the UK, of all ages, but is two to three times as common in women as it is in men. It’s thought hormonal and reproductive factors may be partly to blame for this.
According to Arthritis Research UK, one third of people with the condition stop working within two years of onset due to the pain.
Researchers examined the link between the development of the disease and use of the contraceptive pill, as well as breastfeeding.
They used data from the Swedish Epidemiological Investigation of Rheumatoid Arthritis (EIRA), which included women aged 18 and above, living in a defined area of Sweden between 1996 and 2014.
During this timeframe, 2,809 women were diagnosed with rheumatoid arthritis. Meanwhile 5,312 women, randomly selected from the general population and matched age-wise, acted as a comparison group.
The study, published online in the Annals of the Rheumatic Diseases, revealed that women who used an oral contraceptive at any time had a lower risk of developing rheumatoid arthritis than those who had never done so.
The risk was 15% lower in current users of the pill and 13% lower in past users.
The association was significant for women who tested positive for anti-citrullinated protein antibodies (ACPA), compared with women who had never used an oral contraceptive.
Nine out of 10 people who test positive for ACPA will have rheumatoid arthritis, and the presence of these antibodies may indicate more serious disease.
Using the pill for more than seven years - the average length of use among the study participants - was associated with a 19% lower risk of developing rheumatoid arthritis.
This was the case for those who tested positive and negative for ACPA.
Although a lower risk was also found among women who had breastfed at least one child, this was not significant, researchers said.
They added that no firm conclusions could be drawn about cause and effect, as it is an observational study, and said they were also unable to glean any information about the dose or type of oral contraceptive the women used.
Professor David Isenberg, Arthritis Research UK professor of rheumatology at UCL, told HuffPost UK: “This is a really interesting study that will help us to further understand some of these factors, especially the role of hormones.
“However, what this study doesn’t tell us is exactly how the oral contraceptive pill can help to lower the risk of developing the condition.”