Oral contraception and its possible protection against rheumatoid arthritis.

Abstract

As of February 1991, epidemiologic studies had still not conclusively identified risk factors of rheumatoid arthritis (RA). In the 1970s, the Royal College of General Practitioners conducted a study which indicated that oral contraceptive (OC) use may protect against RA. Scientists have since conducted several other studies, but they have not been able to provide clear answers. OC use caused a fall in RA by about 50% in 7 studies. The results of 1 study was inconclusive. Methodological problems existed for the earliest studies. Even recent studies without these problems conflict with each other. In the late 1980s, 2 meta analyses pooled reported relative risks (RR) of RA for ever users of OCs and found a slight protective effect. 1 analysis separated prior research findings into those from the US and those from Europe. The other analysis pooled the risk ratios for hospital based studies and population based studies separately. Since many studies were hospital based, scientists explained the divergence on patient selection. The preliminary results of a methodological impressive study in Seattle, Washington showed a significant reduction RA risk in current users of OCs, but only slight reduction in past OC users. All of these findings posed 2 possible explanations on how OCs protect against RA: they may prevent progression of mild to severe RA by altering the disease process or they only prevent the development of progressive destructive RA. The Royal College later analyzed recent data and found that the RR of RA among current OC users approximates the RR among former users. The many inconsistencies between these studies suggests that OC use may be a marker for some other casual factor which differs among subjects.