Background and Objectives Multiple sclerosis (MS) prevalence varies widely by country and world region, variation that is often attributed to latitude and its association with vitamin D exposure. Given that increasing latitude is also associated with higher national wealth, this study investigated associations between MS prevalence and other factors driving regional differences, with a focus on sociodemographic, health systems, and lifestyle factors on a national and regional level.
Methods Using data from multilateral organizations and scientific literature, an ecological study was conducted to evaluate associations between age- and sex-adjusted MS prevalence and prespecified sociodemographic (gross domestic product [GDP] per capita and gross national income [GNI] per capita), health systems (current health expenditure per capita and by percentage of GDP, universal health coverage [UHC] index, and medical doctors per capita), neurology-specific (MRI unit density and neurologists per capita), and lifestyle (obesity and tobacco use) factors. National, regional, and income-stratified data were aggregated and employed in relevant univariable and multivariable regression models. Stepwise variable selection techniques identified independent predictors of MS prevalence.
Results Univariable regression analyses showed significant associations at the national level for all investigated factors, except obesity prevalence and tobacco use. Latitude was significantly associated with MS prevalence in all world regions (β = 0.16–2.16), whereas the UHC index was significantly associated in 5 of 6 world regions (β = 0.18–3.17). MS prevalence was significantly associated with all factors except lifestyle factors and MRI unit density in high-income countries, but no associations were observed in low-income countries. Latitude was associated with MS prevalence for all income strata except low-income countries (β = 0.55–1.62). In multivariable analyses, current health expenditure per capita (β = 0.083, 95% CI 0.048–0.12, p < 0.01) and latitude (β = 1.05, 95% CI 0.63–1.47, p < 0.01) remained significantly associated with MS prevalence.
Discussion Health expenditure per capita is strongly associated with national MS prevalence, suggesting that theories that attribute variations in MS prevalence primarily to latitude effects on vitamin D are incomplete. Health care access significantly contributes to the global variations in MS prevalence, especially since national wealth rises with latitude and likely results in significant underestimation of MS prevalence in countries with lower health expenditure.