Oral contraceptives and rheumatoid arthritis : further epidemiologic evidence for a protective effect

In Chapter I the history of the investigation is described: the literature reports that the pill would halve the incidence of rheumatoid arthritis which first drew our attention, our initial views on how to test this hypothesis by means of a case-control study, and the opportunity presented by the rheumatologic registry at the Erasmus University Rotterdam. The aim of the study is stated: to investigate whether the halving of the incidence of rheumatoid arthritis among oral-contraceptive users relative to never-users, as originally described in a follow-up study in Great Britain, would also be demonstrable in a case-control study in the Netherlands. In Chapter II the reasons for starting the investigation are elaborated. First, the relevant literature is critically reviewed. The evidence for a negative association between oral-contraceptive use and the development of rheumatoid arthritis is judged interesting, although still wanting: several objections to the validity of the inference can be formulated. Second, the phenomenon is interesting from a point of view of public health. If the pill protects against a crippling disease which is frequent in women, this might to a certain extent balance the negative aspects of its cardiovascular side-effects. Third, there is a strong biological interest. If the pill causally prevents rheumatoid arthritis, this provides another piece of the puzzle of the pathogenesis of this disease, which advances the state of our knowledge. The fourth and last reason for starting the investigation was the unique opportunity of a rheumatology registry that covers the patients of several of the major rheumatology clinics in the Netherlands.