Individual and Joint Action of Environmental Factors and Risk of MS

This review discusses the leading environmental and lifestyle factors suspected to play a role in the onset of multiple sclerosis (MS). The authors utilize the framework of the Rothman Causal Pie Model1 to discuss the joint action, or interaction, of different factors that that may be causally involved in MS. A key feature of many environmental exposures is that the period of life in which exposure occurs and possibly the timing of a sequence of events can affect how they mediate their effects. Evidence on the timing of each environmental factor is discussed.