Introduction Previous studies have demonstrated a strong latitudinal gradient in multiple sclerosis (MS) prevalence, likely related to interplay between genetic and environmental factors, particularly vitamin D and sun exposure. Herein, we update our 2010 meta-analysis of the latitudinal gradient of MS prevalence, seeking to assess the presence and magnitude of the gradient and whether it has changed since our 2010 analysis.

Methods Studies published between 2010 and 2017 were located via EMBASE, ISI and PubMed, using standardised search terms; data was extracted from peer-reviewed studies. These studies were added to the studies collected in our previous analysis. Prevalence estimates were adjusted for study prevalence year. Where age/sex-specific data were available, prevalence values were age/sex standardised to the 2009 European population. For the 2010–2017 interval, 85 prevalence studies were found, 53 of which met inclusion criteria, yielding 108 new prevalence points. The latitudinal association with MS prevalence was assessed by meta-regression.

Results There was a significant positive gradient in MS prevalence with increasing latitude (6.89/100,000 per degree latitude), attenuating slightly to 5.60/100,000 on age-standardisation, these associations persisting on adjustment for diagnostic criteria used. Of note, the age-standardised gradient was significantly stronger (p=0.044) than that from our previous study.

Conclusion This updated meta-analysis confirms that MS prevalence is still strongly positively associated with increasing latitude.