Environmental factors: Possible reasons for higher incidence and prevalence of multiple sclerosis in high-income countries

Background: Multiple sclerosis (MS) has had a remarkable increase in prevalence during recent years. This study was conducted to evaluate the correlation between prevalence and incidence of MS with the income level and lifestyle condition of countries with considering the effect of latitude. Subjects and Methods: This is an ecological study with secondary data obtained from several sources such as MS International Federation for MS variables data, and World Bank is a reliable source for economic variables. The latitude is also added in all models as an important effective factor. The bivariate correlation and linear regression were used to analyze of data. Results: The prevalence of MS in 2013 (54.06/100,000) increased by 9% in comparison to that in 2008 (49.96/100,000). According to fully adjusted analysis, there were significant positive correlations between income level with the incidence and prevalence of MS in reported 2008 and 2013 (P < 0.05) throughout the world. Our results revealed that the mean MS prevalence estimates in northern hemisphere, especially in North of America and Europe were different with those in the southern hemisphere. Conclusion: MS is more prevalent in high-income countries and the prevalence in developing countries is increasing by economically growth. It seems that environmental factors related to economic determinants are associated with increased incidence and prevalence of MS, further, geographic location continues to influence risk for MS, but these associations require more studies.