Prenatal Exposure to Tobacco Smoke May Increase MS Risk

Smoking tobacco during pregnancy may increase an offspring’s risk of developing multiple sclerosis (MS), according to a study published in Multiple Sclerosis Journal.

MS, while not completely understood, has been associated with a myriad of genetic and environmental factors. One of these environmental components is smoking or exposure to tobacco smoke. The authors of the present study point to a meta-analysis conducted in the last decade that detailed an odds ratio for MS of 1.55 (95% CI, 1.48-1.62) for smokers compared with non-smokers.

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During pregnancy, smoking has long been linked to detriments in fetal development as it can affect an offspring’s immune system and brain, increasing their risks for certain diseases. Research tracking MS risks associated with smoking during pregnancy have not offered coherent conclusions on its impact. As the authors mention, results in these studies have ranged from no found associations to suggesting offspring endure triple the risk of MS development.

To explore the relationship between smoking during pregnancy and MS risk further, researchers conducted 2 population-based cohort studies with data gathered from the multiple Danish registers including the Danish Medical Birth Register (MBR). Data on smoking during pregnancy became available in 1991. Therefore, a cohort of Danish-born women who had given birth were identified from 1991 through 2018. To identify MS cases of offspring and their mothers, the Danish National Patient Register (NPR) was used. Researchers used 2 forms of hazard ratios (HRs) in their analysis: HR1 (analyzed age, sex [offspring] and birth), HR2 (considered the mother’s risk of MS, as well as adjusted for infectious mononucleosis [IM] and obesity cofounders), and H3 (took birth weight into account).

Throughout the study period, 789,299 women were pregnant, of whom 3591 developed MS during follow-up. Of the women registered as smokers during their pregnancy, results detailed that they carried a 1.42-fold increased risk of MS (HR1, 1.42; 95% CI, 1.32-1.52; HR2 was identical) compared with those who did not smoke during pregnancy.

A total of 879,135 babies were born throughout the study period and at follow-up 293 were diagnosed with MS. Thirty-eight percent (n = 110) of babies had endured intrauterine exposure to tobacco smoke. Analysis revealed that this prenatal exposure increased their risk of MS by 31% (HR1: 1.31; 95% CI, 1.04-1.67; HR2: 1.31; 95% CI, 1.03-1.66]). Adjustments for birth weight slightly increased this risk (HR3, 1.38; 95% CI, 1.08-1.76).

The authors highlighted that these results reinforce past research on the associations between smoking and the risk of MS. Furthermore, their findings added to this knowledge by suggesting that individuals exposed to tobacco prenatally may carry an increased risk as well. However, the authors were unable to discern whether the observed increase of MS risk was associated with smoking later in life or passively over the years.

Reference

Nielson NM, Frisch M, Gørtz S, et al. Smoking during pregnancy and risk of multiple sclerosis in offspring and mother: a Danish nationwide register-based cohort study. Mult Scler. Published online November 19, 2023. doi:10.1177/13524585231208310