By Jane Lewis
Oral contraceptive (OC) use is associated with a significantly lower risk of rheumatoid arthritis (RA), according to research published in the Annals of the Rheumatic Diseases.
Commenting on the findings, rheumatologist Professor Rachelle Buchbinder, Director of the Monash Department of Clinical Epidemiology, Cabrini Institute, Melbourne, said the study was a good example of how ‘population-based, long-term observational studies provide very valuable information for looking at risk factors as well as long-term benefits/harms of treatment.’
The research was based on data from women aged 18 years and over who took part in the Swedish Epidemiological Investigation of Rheumatoid Arthritis, described by the study authors as ‘one of the largest population-based case–control studies comprising incident cases of RA with concordant information on environmental and genetic factors.’
Participants in the study (2641 cases and 4251 controls) completed an in-depth questionnaire regarding lifestyle and environmental exposures, including OC use, breastfeeding and potential confounders such as alcohol consumption and smoking. Ever users of an OC were found to have a decreased risk of developing RA overall, compared with those who had never used an OC. When stratified by the presence or absence of anticitrullinated protein antibodies (ACPA), the association was only significant for ACPA-positive RA in both crude and adjusted models. A significant dose–response association was observed for duration of OC use, with long term use (more than seven years) decreasing the risk of both ACPA-positive and ACPA-negative RA.
A history of long breastfeeding duration decreased the risk of ACPA-positive RA, in a dose dependent manner, but this trend did not remain after adjustments.
A significant interaction was seen between the lack of OC use and smoking on the risk of ACPA-positive RA.
‘This study confirms that oral contraceptive use decreases the risk of rheumatoid arthritis, especially ACPA-positive rheumatoid arthritis,’ commented Professor Buchbinder, adding that this protective effect was not a reason to take an OC. ‘Breast feeding may also be protective, and this is another reason why breastfeeding is a good thing.’
‘The beauty of these data is that they are based on a high quality large population-based study, so the results are trustworthy and likely generalisable.’
The authors suggested further research was needed to explore the biological mechanisms behind the findings, and to investigate whether hormonal factors have a different impact on the ACPA-subsets of RA.
Ann Rheum Dis 2017; doi:10.1136/annrheumdis-2017-211620.