Modifiable environmental factors – Role and impact of (including evidence for intervention)

Abstract

It is now generally accepted that multiple sclerosis (MS) is a multifactorial disease occurring in genetically susceptible individuals upon exposure to environmental factors. The importance of environmental factors in MS is supported by discordance in monozygotic twins, geographical distribution of MS prevalence, migration studies, increase in MS incidence and changes of gender ratio over time, among others. Robust evidence supports the role of EBV, smoking, UV radiation/vitamin D and obesity during adolescence as environmental factors. Some evidence also suggests the involvement of other factors such as night shift work, organic solvents, concussions, salt intake, melatonin, parasites, coffee and alcohol consumption as well as dysbiosis of the gut microbiome. Environmental factors play a role not only in the susceptibility to develop MS but also in disease activity and disability progression. Furthermore, it has been shown that environmental factors interact among one another and with genetic factors. Whether there is a critical time period during which exposure to these factors is most important is still not fully understood. However, modifying these factors once MS is established might still have an impact in the disease course, as is the case of smoking cessation. Overall, this suggests that interventions directed towards modifying environmental and lifestyle factors could prevent some MS cases and improve the prognosis in MS patients. However, our understanding of the underlying pathogenic mechanisms of these factors and the impact of their modification is still limited. Future research to identify other environmental factors and to investigate the impact of intervention over known environmental factors is necessary.