Epub: Magyari et al. Reproduction and the risk of multiple sclerosis. Mult Scler. 2013 Mar 18.
BACKGROUND: The incidence of multiple sclerosis (MS) in Denmark has doubled in women since 1970, whereas it has been almost unchanged in men.
OBJECTIVES: To investigate whether age at first childbirth and number of births have an effect on the risk of developing MS.
METHODS: The cohort consisted of 1403 patients with MS of both sexes, identified through the Danish Multiple Sclerosis Registry, with clinical onset between 2000 and 2004. For each case, 25 control persons were drawn by random from the Danish Civil Registration System matched by sex, year of birth, and residential municipality.
RESULTS: More female cases than controls had no childbirths or fewer births before clinical onset (p=0.018) but only in the last five years preceding onset (p<0.0001). Childbirths within five years before clinical onset reduced the risk of MS onset in women: OR=0.54 (95% CI 0.41-0.70, p<0.0001) for one child and OR=0.68 (95% CI 0.53-0.87, p=0.002) for more than one child. Parental age at first childbirth had no effect on the risk of MS.
CONCLUSIONS: The data did not suggest reversed causality between childbirth and MS.
RESULTS: More female cases than controls had no childbirths or fewer births before clinical onset (p=0.018) but only in the last five years preceding onset (p<0.0001). Childbirths within five years before clinical onset reduced the risk of MS onset in women: OR=0.54 (95% CI 0.41-0.70, p<0.0001) for one child and OR=0.68 (95% CI 0.53-0.87, p=0.002) for more than one child. Parental age at first childbirth had no effect on the risk of MS.
CONCLUSIONS: The data did not suggest reversed causality between childbirth and MS.
The study suggests that if you have children you are less likely (about twice less likely) to develop MS, within 5 years, than if you are a female and did not have children. This may suggest some hormonal influence and we know that being pregnant inhibits your immune response. In Europe the average age at time of first born is about 26-29, in the 1970s it was 23-25. Is this part of the equation in the increase in MS in women? Maybe not in this study. Is this the case elsewhere?