Latitude and UVB exposure linked to multiple sclerosis severity: study

Australia: Severity of multiple sclerosis (MS) is associated with latitude and this association is partly driven by UVB exposure contributing to both MS susceptibility and severity, states an article published in the journal Neurology.

Globally, nearly 3 million people are affected by multiple sclerosis (MS), a chronic disease affecting the central nervous system. There is a complex interplay between genetic and environmental factors for both development of MS and symptomology. The latitudinal gradient is one of the strongest geo-epidemiological findings in multiple sclerosis risk studies.

Previously, data have shown a rising prevalence rate of MS towards the poles and the lowest prevalence rate in equatorial regions. This gradient may be the consequence of varying sunlight exposure along the latitudinal bands. The effect of UVB on generating vitamin D seems the most likely candidate for explaining its relationship with MS.Understanding the determinants of this heterogeneity will help clinicians optimize the management of MS.

Marianna V., University of Melbourne, Australia, and her research team conducted an observational study using international registry data to investigate the association between the latitude of residence, UV B radiation (UVB) exposure, and the severity of MS.

Researchers used the MSBase registry data. The enrolled patients met the 2005 or 2010 McDonald diagnostic criteria for MS and had a minimum dataset recorded in the registry (date of birth, sex, clinic location, date of MS symptom onset, disease phenotype at baseline and censoring, and ≥1 Expanded Disability Status Scale score recorded).

They calculated the latitude of each study center and cumulative annualized UVB dose at the study center at ages 6 and 18 years and the year of disability assessment. Disease severity was quantified with the Multiple Sclerosis Severity Score (MSSS). Quadratic regression was used to model the associations between latitude, UVB, and MSSS.

Key findings of the study: 

• Latitude showed a nonlinear association with MS severity

• In latitudes above 40°, a higher latitude was associated with the more severe disease with the Multiple Sclerosis Severity Score increasing by 0.08 points for every degree of latitude. This association was not observed in latitudes below 40°.

• The overall Disability accrual was faster in those with a lower level of estimated exposure to UVB radiation, particularly at early ages, as well as with lower lifetime UVB exposure at the time of disability assessment

Researchers conclude that there is an association between the severity of multiple sclerosis and latitude, at latitudes above 40° and ultraviolet B (UVB) exposure contributes partly to this association.

Reference:

Marianna Vitkova, Ibrahima Diouf, Charles Malpas, Dana Horakova, Eva Kubala Havrdova, Francesco Patti et al. Association of Latitude and Exposure to Ultraviolet B Radiation With Severity of Multiple Sclerosis, An International Registry Study, Neurology Jun 2022, 98 (24) e2401-e2412; DOI: 10.1212/WNL.0000000000200545