Rates of multiple sclerosis (MS) appear to rise with measures of prosperity, occurring more frequently in developed countries, according to a recent study.
The reasons for such disparities may be linked to better access to diagnostic facilities in developed countries, as well as increased exposure to factors, such as obesity or smoking, that increase the risk for MS. This should be investigated in greater detail, researchers advise.
The study, “Socioeconomic determinants of global distribution of multiple sclerosis: an ecological investigation based on Global Burden of Disease data,” was published in the journal BMC Neurology.
The prevalence and incidence of MS vary broadly around the world, suggesting that environmental factors interact with genetics to trigger the condition. Prevalence is the number of cases in a certain population at a given time, while incidence is the number of new cases in that population over a period of time.
Because an individuals’ lifestyles influence which environmental risk factors they might be exposed to, socioeconomic components also may be linked to MS.
To test this hypothesis, scientists from the Torbat Heydariyeh University of Medical Sciences, in Iran, compared MS rates in various countries to those regions’ socioeconomic status, as measured by the Human Development Index (HDI) and Prosperity Index (PI).
HDI provides a way to compare socioeconomic differences between countries, while PI is used to evaluate community-level social well-being, based on the state of health services, environmental conditions, and governmental power.
“Taken together, these two indices represent the extent of countries’ development,” the researchers wrote.
Using available data, collected in 2017 from 195 countries, the team found that, overall, 21.7 people per 100,000 had MS, and that MS cases occurred at a rate of 0.7 per 100,000 people.
Canada showed the highest prevalence, at 168 people per 100,000, and the highest incidence, at 5.63 per 100,000. At the other end of the scale, the island nation of Maldives had the lowest prevalence and incidence, at 1.52 and 0.09 per 100,000 people, respectively.
Among countries with available socioeconomic measures, Norway and Yemen had the highest and lowest PIs, respectively. Norway also had the highest HDI, while Niger had the lowest.
In general, rates of MS correlated strongly with prosperity measures. Countries in North America and Western Europe tended to have higher HDI and PI, and had the greatest numbers of MS, both as a proportion of their populations (MS prevalence) and in terms of growing cases (MS incidence).
On average, 54.21 and 11.64 people had MS per 100,000 in developed and developing countries, respectively, and MS incidence in developed countries was 5.5 times that of developing nations.
The investigators observed that within PI subgroups, MS rates tended to increase more with health status, state stability, and higher education, than with any other factors. On the other hand, expected years of schooling and gross income were the HDI factors more strongly associated with MS measures.
The differences between developed and developing countries could be due, in part, to better access to diagnostic facilities in developed nations, leading to earlier and more widespread diagnosis and treatment. Better socioeconomic conditions also associate with things like increased rates of smoking and obesity, which are potential MS risk factors.
Higher infant mortality rates in the developing world also could influence MS rates, the scientists wrote, as this could allow fewer people with compromised immune systems — such as those with MS — to reach adulthood.
“In general,” the researchers concluded, “the difference in income and the socioeconomic development globally have created a landscape for MS that should be studied in more detail in future studies.”
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