Latitude continues to be significantly associated with the prevalence of multiple sclerosis: an updated meta-analysis

Abstract

ObjectivesPrevious studies have demonstrated a strong latitudinal gradient in multiple sclerosis (MS) prevalence. Herein, we present a meta-analysis of the latitudinal gradient of MS prevalence including studies published since our 2011 review, seeking to assess the latitudinal gradient and whether it has changed since our previous analysis.MethodsStudies published up to December 2018 were located via Embase, Web of Knowledge and PubMed, using standardised search terms; data were extracted from peer-reviewed studies and these studies added to those from our previous analysis. Where age-specific data were available, prevalence estimates were age-/sex-standardised to the 2009 European population. Prevalence estimates were adjusted for study prevalence year and ascertainment methods. The latitudinal association with MS prevalence was assessed by meta-regression.ResultsA total of 94 studies met inclusion criteria, yielding 230 new prevalence points and 880 altogether with those from the prior study. There was a significant positive gradient in time-corrected MS prevalence with increasing latitude (5.27/100 000 per degree latitude), attenuating slightly to 4.34/100 000 on age-standardisation, these associations persisting on adjustment for ascertainment method. Of note, the age-standardised gradient was consistently significantly enhanced from our previous study, regardless of whether it was as-measured, time-corrected or adjusted for ascertainment methods. Certain areas, such as the Scandinavian and Atlantic Coast/Central Europe regions, showed changes in MS prevalence gradient over time, but other regional gradients were similar.ConclusionsThis new meta-analysis confirms that MS prevalence is still strongly positively associated with increasing latitude and that the gradient is increasing, suggesting that potentially modifiable environmental factors, such as sun exposure, are still strongly associated with MS risk.

Long-term effects of latitude, ambient temperature, and ultraviolet radiation on the incidence of multiple sclerosis in two cohorts of US women

“…Furthermore, our study confirmed the attenuation of North-South differences observed in more recent time periods, in some, but not all, studies or regions of the world. 5 , 39 This attenuation may be due to increased time spent indoors, changes in sun behaviors, or increased use of sunscreens. 40 However, in a recent meta-analysis of 415 (321 studies from a previous meta-analysis and 94 new studies) studies examining the association of latitude and MS prevalence, a comparison of slopes derived from 2008 to those in 2018 demonstrated statistically significant increases in risk from more recent studies, suggesting these attenuations may not be true across the literature.…”

Immunoregulatory effects and therapeutic potential of vitamin D in multiple sclerosis

“…A recent meta-analysis revealed that the latitudinal variation of MS prevalence has increased over time (Simpson et al, 2019). The key candidates to explain these findings are UVB exposure and vitamin D status.…”

“…The presence of a latitudinal gradient of MS prevalence and incidence, increasing with distance away from the equator, is a key environmental risk factor. A recent meta‐analysis revealed that the latitudinal variation of MS prevalence has increased over time (Simpson et al, 2019). The key candidates to explain these findings are UVB exposure and vitamin D status.…”

Narrowband UVB phototherapy reduces TNF production by B‐cell subsets stimulated via TLR7 from individuals with early multiple sclerosis

“…1 Ecologic studies support the concept of latitude gradients for the incidence, prevalence and mortality of MS, with more disease at higher latitudes where there is generally less sun exposure. 2,3 Many have suggested that low vitamin D status is responsible for these observations. 4,5 The main source of 25-hydroxy vitamin D (25(OH)D) for humans is derived following exposure of skin to the UVB components of sunlight.…”