University of Manchester, Oxford Road, Manchester, UK
SIR, We would like to thank Dr Zauli and her colleagues for their interest in our paper in which we reported a fall in the prevalence of rheumatoid arthritis (RA) in the UK [1] since the 1950s. This fall was observed in women but not in men. We suggested that the observed changes in prevalence might be explained by a protective effect of the oral contraceptive pill or another factor related to taking the pill. They suggest an interesting alternative hypothesis, namely that the presence of atopy confers some protection against RA and that the observed changes in the prevalence of RA may be attributed to an increase in the prevalence of atopy. The two hypotheses are not, of course, mutually exclusive and both might play a role.
For the atopy theory to be the predominant explanation there would be a need for the prevalence of atopy to have increased in women but fallen in men. Zauli et al. report a low prevalence of RA in a group of 1937 adults attending an allergy clinic. In order to interpret this low prevalence, we need to know the expected number of cases in an age- and sex-matched sample of the general Italian population. The prevalence of RA in Italy is probably lower than in the UK [2]. There would also be a need to consider whether the attenders at the allergy clinic are representative of all Italian atopic subjects or whether there may be some referral bias.
Notes
E-mail: deborah.symmons{at}man.ac.uk
References
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