The global incidence trends of multiple sclerosis (MS) show a clear relationship with urbanization and lifestyle changes, reflecting a complex interplay of environmental, social, and biological factors. MS, an autoimmune disease affecting the central nervous system, has historically been more prevalent in higher latitude regions such as Europe and North America, but recent decades have seen rising incidence rates in urbanized areas worldwide, including parts of the Middle East and Asia.
Urbanization contributes to MS incidence through several pathways. First, urban environments often involve lifestyle shifts that include reduced exposure to natural sunlight, leading to lower vitamin D levels. Vitamin D deficiency is strongly implicated in MS risk because it plays a critical role in immune regulation and inflammation control. Urban dwellers typically spend more time indoors, have less physical activity, and may have diets lower in vitamin D, all of which can increase susceptibility to MS. This is particularly evident in rapidly urbanizing countries where traditional outdoor lifestyles are replaced by more sedentary, indoor habits.
Second, urbanization is associated with increased exposure to environmental pollutants and toxins, which can trigger or exacerbate autoimmune responses. Air pollution, industrial chemicals, and other urban environmental stressors may contribute to neuroinflammation, a key pathological process in MS. These factors can disrupt the blood-brain barrier and activate immune cells that attack myelin, the protective sheath around nerve fibers.
Third, lifestyle changes linked to urban living include altered dietary patterns, increased psychosocial stress, and changes in infection exposure. Diets high in processed foods and low in antioxidants may promote oxidative stress and inflammation, worsening MS risk. Psychosocial stress, more common in densely populated urban areas, can dysregulate immune function, potentially triggering autoimmune diseases. Additionally, urbanization often changes patterns of childhood infections and hygiene, which may influence immune system development and MS susceptibility through the “hygiene hypothesis”—the idea that reduced early-life exposure to microbes can lead to immune dysregulation.
Epidemiological data support these connections. Regions undergoing rapid urbanization, such as parts of Iran and Brazil, have reported rising MS prevalence, sometimes exceeding 80 to 100 cases per 100,000 population in urban centers. This increase is partly due to better diagnostic capabilities but also reflects genuine rises linked to lifestyle and environmental changes. In contrast, rural or less urbanized regions tend to have lower MS incidence, likely due to greater sunlight exposure, different infection patterns, and less exposure to urban pollutants.
Moreover, socioeconomic factors tied to urbanization influence MS trends. High-income urban areas often have better healthcare infrastructure, leading to improved disease detection and reporting, which can inflate apparent incidence rates. However, disparities within urban populations also exist, where lower socioeconomic status correlates with higher MS burden due to factors like limited access to nutritious food, healthcare, and increased stress.
In summary, the global rise in MS incidence correlates strongly with urbanization and associated lifestyle changes. Reduced sunlight exposure and vitamin D deficiency, increased environmental pollutants, dietary shifts, psychosocial stress, and altered infection patterns all contribute to this trend. These factors interact with genetic predispositions and social determinants of health, creating a multifaceted landscape where urban living environments significantly influence MS risk and prevalence.
