Environmental risk factors in multiple sclerosis

A coherent consensus regarding the etiology of multiple sclerosis (MS) and immune-mediated chronic diseases (such as rheumatoid arthritis, juvenile diabetes, and autoimmune thyroid disease) has emerged over the past two decades: exogenous (including infectious), environmental, or behavioral (lifestyle) factors cause disease onset in genetically susceptible persons.1 Neither genes by themselves nor exogenous factors alone are sufficient to cause MS. The likely scenario is that, in a genetically susceptible person, the equilibrium among components of the trimolecular complex (major histocompatibility complex molecules, T-cell receptors, and foreign or self antigens) is disrupted sufficiently to induce a chronic state of autoimmune damage.2 Despite theories, however, no infectious agent has been established as a causal agent in MS. An environmental etiology for MS is suggested by the strong north–south gradient in disease frequency, by disease clusters, and by evidence that migration to and from high-risk areas in early life influences the likelihood of developing MS.

More sophisticated investigations regarding lifestyle factors associated with MS have recently emerged. Smoking appears to have important but modest associations with MS and other autoimmune disorders; the basis for this association …