Researchers have known people who live farther from the equator are more likely to develop multiple sclerosis (MS) and have often attributed that to vitamin D exposure. But countries farther from the equator are also more likely to be wealthier than countries nearer to the equator. A new analysis shows that the amount a country spends on health care may help explain the link between MS and latitude. This new research is published in the August 24, 2022, online issue of Neurology®, the medical journal of the American Academy of Neurology.
According to study author Deanna Saylor, MD, MHS, of Johns Hopkins University School of Medicine in Baltimore and a member of the American Academy of Neurology, the results suggest that MS rates may be greatly underestimated in low-income countries with lower health care 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.
For the analysis, researchers analyzed data from scientific studies and databases to determine current rates of MS in 203 countries and territories. They then grouped these countries into world regions and by income levels.
Rates of MS varied by region and income level. For example, in high-income countries an average of 46 of every 100,000 people had MS, compared to 10 people per 100,000 in low-income countries. Health care spending per capita was $2,805 for high-income countries, compared to $45 in low-income countries.
For each location, researchers 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 the researchers adjusted the data for other factors that could affect the risk of MS, such as age and sex, they found that health care spending and latitude were strongly associated with MS rates. The research showed that, 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.
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