The link between higher multiple sclerosis rates and distance from the equator has commonly been explained by vitamin D levels. A new analysis from Johns Hopkins researchers suggests the association may also be linked to healthcare spending and the resources needed to diagnose disease.
People who live farther from the equator are more likely to develop multiple sclerosis (MS), which is often attributed to sunlight and associated vitamin D levels.
However, countries farther from the equator are also more likely to be wealthier than countries closer to the equator, the American Academy of Neurology noted in a news release. In the same vein, a new analysis, published in Neurology, shows that the amount a country spends on healthcare may help explain the link between MS and latitude.
Deanna Saylor, M.D.,the senior author of the study and an associate professor of neurology at Johns Hopkins University School of Medicine, and colleagues analyzed data from scientific studies and databases to determine current rates of MS in 203 countries and territories.
Next, they grouped the countries into world regions and by income levels. They examined gross domestic product per capita, current health expenditure per capita, income levels, the availability of brain scans to diagnose MS, the number of neurologists per capita, and universal health care. They also reviewed lifestyle factors such as obesity and tobacco use.
Once Saylor and team adjusted the data for other factors that could affect the risk of MS, such as age and sex, they found that healthcare spending and latitude were strongly associated with MS rates.
With every increase of one standard deviation in health expenditure per capita, a country’s MS prevalence increased by 0.49. Alternatively, with every increase of one standard deviation in latitude, a country’s MS prevalence increased by 0.65.
In high-income countries, an average of 46 of every 100,000 people had a MS diagnosis, compared to 10 people per 100,000 in low-income countries. Healthcare spending per capita was $2,805 for high-income countries, compared to $45 in low-income countries.
“The results suggest that MS rates may be greatly underestimated in low-income countries with lower healthcare spending, which means that people have less access to neurologists who have the expertise to diagnose MS and MRI scanners that are needed to make the diagnosis,” AAN said.
The availability of universal healthcare was associated with rates of MS in all world regions, except Southeast Asia.
In high-income countries, rates of MS were linked to most factors, including gross domestic product per capita, current health expenditure per capita, and the number of neurologists, but not tobacco use and obesity or the number of MRI units per capita.
The minimal links between rates of MS and lifestyle factors such as tobacco use and obesity run counter to prior assumptions that lifestyle and consumption behaviors explain the large portions of regional differences in reported rates of MS, Saylor wrote.
In low-income countries, there were no associations with any of the factorsthe researchers reviewed, which may be attributed to a lack of significant variation in data from these countries, Saylor said.
The fact that current health expenditure per capita was very strongly linked with national rates of MS further supports the hypothesis that greater investment in healthcare leads to more robust reporting of rates of MS, Saylor noted.
Strategies are “urgently needed” to lessen the shortages in trained professionals and critical technology that prevent the accurate assessment of the burden of MS in low-income countries, according to Saylor.
The study was supported by the National Multiple Sclerosis Society.