Role of socio-economic and reproductive factors in the risk of multiple sclerosis.

The incidence of multiple sclerosis is increasing in Danish women. Their risk of developing multiple sclerosis has more than doubled in 25 years while it has remained virtually unchanged for men. The explanation for these epidemiological changes should be sought in the environment as they are too rapid to be explained by gene alterations. We investigated the effect of numerous biological social physical and chemical environmental exposures in different periods of life. These data were available from population-based registries and were used in a case-control approach. This study database included all multiple sclerosis cases (n = 1403) from the Danish MS Registry with clinical onset between 2000 and 2004 as well as 35,045 controls drawn by random from the Danish Civil Registration System and matched by sex year of birth and residential municipality at the reference year. Having newborn children reduced the risk of multiple sclerosis (MS) in women but not in men. Childbirths reduced the risk of MS by about 46% during the following 5 years. Even pregnancies terminated early had a protective effect on the risk of developing MS suggesting a temporary immunosuppression during pregnancy. Our data on social behaviour regarding educational level income and relationship stability did not indicate reverse causality. A greater likelihood to be exposed to common infections did not show any effect on the risk of MS neither in puberty nor in adulthood. Socio-economic status and lifestyle expressed in educational level and sanitary conditions in youth were not associated with the risk of MS.