Parental smoking exposure and risk for multiple sclerosis among adults: The EnvIMS study

Background and aims: Active smoking is a known risk factor for Multiple sclerosis (MS) development and poor prognosis. However, the impact of past exposure to parental smoking (ParS), including maternal smoking during pregnancy (MSDP) is not well defined. We aimed to investigate how these types of early age exposures affect MS risk among adults. Methods: Using the data collected by the EnvIMS study, a large multinational case–control population-based study, we investigated the association between MS and smoking habit, MSDP and maternal/paternal smoking (MaS, PaS) in Canadian, Italian, and Norwegian populations. Data were collected with EnvIMS-Q, designed to investigate environmental exposures during early life stages. Adjusted odds ratios (aOR) for index age and participants' smoking status are presented with 95% confidence intervals (95% CI). Results: We included 1565 Canadian, 2040 Italian, and 2674 Norwegian subjects. An association between MS and MSDP and MaS was observed among Norwegians: aOR 1.38 (1.12, 1.71) and 1.39 (1.17, 1.65), respectively. A tendency for PaS to be associated with MS was found among Canadians: aOR 1.21 (0.97, 1.51). No significant association to ParS (any) was detected in the Italian population. Conclusion: Selective exposure to ParS at early age may differentially increase MS risk in the general population and independently from the subject's past/current smoking habit. The developmental origin of health and disease (‘DOHaD’) theory may help interpret these findings. The absence of an association between MS and past exposure to ParS in other populations may reflect its smaller effect on MS risk compared to other factors.