The pill, parity, and rheumatoid arthritis

Authors

  • Dr. Tim D. Spector Msc, Mrcp,

    Corresponding author
    1. Department of Epidemiology, The London Hospital Medical College, and The London School of Hygiene and Tropical Medicine, London, United Kingdom.
    Current affiliation:
    1. Department of Rheumatology, St. Bartholomew's Hospital, London, UK
    • Department of Rheumatology, St. Bartholomew's Hospital, London EC1A 7BE, UK
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  • Eve Roman PhD,

    1. Department of Epidemiology, The London Hospital Medical College, and The London School of Hygiene and Tropical Medicine, London, United Kingdom.
    Current affiliation:
    1. Arthritis and Rheumatism Council Epidemiology Research Unit, Manchester, UK
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  • Alan J. Silman MdFfcm

    1. Department of Epidemiology, The London Hospital Medical College, and The London School of Hygiene and Tropical Medicine, London, United Kingdom.
    Current affiliation:
    1. Arthritis and Rheumatism Council Epidemiology Research Unit, Manchester, UK
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Abstract

We report on a case-control study investigating the relationship of oral contraceptive pill (OCP) use and parity to the development of rheumatoid arthritis (RA). Women with RA were compared with 2 separate control groups, women with osteoarthritis (OA) and women randomly selected from a population-based electoral register. Nulliparity was found to be a risk factor for the development of RA, with age-adjusted odds ratios of 1.82 (95% confidence interval [CI] 1.09-3.03) versus the OA control group and 1.83 (95% CI 1.03–3.06) versus the population control group. Use of OCPs before the age of 35 was negatively associated with RA (odds ratio 0.56, 95% CI 0.29–1.12 versus the OA control group; odds ratio 0.6, 95% CI 0.30–1.17 versus the population control group). Some evidence of a duration-response effect was seen, although the numbers were small. The 2 variables were also multiplicative, with nulliparous non-OCP users having a 4-fold risk of RA compared with parous OCP users. These findings suggest that pregnancy and OCP use have a “protective effect” on the development of RA, although the mechanism remains unclear.

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