Oral contraceptives protective against rheumatoid arthritis
Oral contraceptives (OCs) may cut the risk of developing rheumatoid arthritis (RA), especially anticitrullinated protein antibodies (ACPA)-positive RA, a study has found. Furthermore, long duration of OC use protects against the risk of both ACPA-positive and ACPA-negative RA.
The study included 2,641 female RA patients and 4,251 matched non-RA controls. Of the RA patients, majority were ACPA-positive (66.5 percent). The mean age at baseline was 50.9 years in the ACPA-positive group and 52 years in the ACPA-negative group.
Data on OC, breastfeeding and potential confounders were obtained from a questionnaire. Analysis was performed using unconditional logistic regression, with adjustments for age, residential area, smoking and alcohol consumption. Attributable proportion due to interaction (AP) was estimated to evaluate presence of interaction.
Compared with OC never-use, ever and past use reduced the risk of developing ACPA-positive RA by 16 and 17 percent, respectively (odds ratio [OR] with ever OC use, 0.84; 95 percent CI, 0.74 to 0.96; OR with past OC use, 0.83; 0.73 to 0.95). No significant associations were observed for ACPA-negative RA.
Of note, long duration of OC use (>7 years vs never use) was associated with reduced risk of both ACPA-positive (p=0.0037) and ACPA-negative RA (p=0.0356). A history of long breastfeeding cut the risk of ACPA-positive RA in a dose-dependent manner (p=0.0086), although this trend disappeared after adjustments.
There was a significant interaction between the lack of OC use and smoking (attributable proportion due to interaction, 0.28; 0.14 to 0.42) on the risk of ACPA-positive RA, suggesting that the risk of ACPA-positive RA was higher among female smokers who never used OCs vs those who did. No interactions were found for breastfeeding.
“The protective effect of OC use on the risk of ACPA-positive RA is in line with our previous finding of a reduced risk of ACPA-positive RA, among women who used postmenopausal hormone therapy. On the other hand, the finding of a protective effect of breastfeeding on the risk of ACPA-positive (in the crude model), but not ACPA-negative RA, is in line with our previous finding of a risk of ACPA-negative but not ACPA-positive RA during the postpartum period. All of these findings together support the notion of RA as two different disease entities with different risk factors patterns,” researchers said.