Health Spending vs ‘Latitude Hypothesis’ for Higher MS Prevalence

How much a country spends on healthcare may have greater bearing on global variations in multiple sclerosis (MS) prevalence than distance from the equator, suggests new research that contradicts a popular theory.

Countries located closest to the equator have a significantly lower MS caseload than countries farther away. The explanation for this, according to the “latitude hypothesis,” is that exposure to sunlight is increased among those living close to the equator. This results in higher vitamin D levels, which may have a protective effect against MS.

The new findings offer a different hypothesis. Countries located farther from the equator are wealthier, with more neurologists who specialize in MS and greater access to MRI scanners needed to diagnose the condition, the investigators note.

“Thus, a shortage or lack of neurologists is likely to result in underestimated prevalence estimates of neurological disorders like MS,” Soonmyung Hwang, BS, Department of Neurology, Johns Hopkins University School of Medicine, Baltimore, Maryland, and colleagues write.

The findings were published online August 24 in Neurology.

National Income, Health Expenditure

Researchers analyzed data from scientific studies and databases to determine current rates of MS in 203 countries and territories. They then organized the countries into world regions and by income levels.

They examined gross domestic product (GDP) per capita, current health expenditure per capita, gross national income, the availability of brain scans to diagnose MS, the number of neurologists per capita, and universal healthcare. The investigators also reviewed lifestyle factors, such as obesity and tobacco use.

In high-income countries, about 46 of every 100,000 people had MS, compared with 10 people per 100,000 in low-income countries. Healthcare spending per capita was $2805 for high-income countries, vs $45 for low-income countries.

Tobacco use, obesity, and similar factors were associated with increased MS prevalence on univariate analysis. However, after multivariable analyses, only current health expenditure per capita (P < .01) and latitude (P < .01) remained significantly associated with MS prevalence.

The findings suggest that a better national economic picture can lead to greater investment in healthcare resources and diagnostic technology, “ultimately driving increased recognition and diagnosis of MS,” the investigators write.

“Furthermore, the largely insignificant associations between MS prevalence and lifestyle factors such as tobacco use and obesity do not support prior hypotheses that lifestyle and consumption behaviors are major factors underlying the association between GDP per capita and MS prevalence,” they add.

The study was funded by a National Multiple Sclerosis Society pilot grant. Saylor received funding from the National Multiple Sclerosis Society that partially supported this work. The other investigators report no relevant financial relationships.

Neurology. Published online August 24, 2022. Abstract

Kelli Whitlock Burton is a reporter for Medscape Medical News who covers psychiatry and neurology.

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