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Latitude is significantly associated with the prevalence of multiple sclerosis: a meta-analysis

Citation

Simpson Jr, S and Blizzard, L and Otahal, P and Van der Mei, I and Taylor, B, Latitude is significantly associated with the prevalence of multiple sclerosis: a meta-analysis, Journal of Neurology, Neurosurgery and Psychiatry, 82, (10) pp. 1132-1141. ISSN 0022-3050 (2011) [Refereed Article]


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Copyright 2011 British Medical Journal Publishing Group.

DOI: doi:10.1136/jnnp.2011.240432

Abstract

Background: There is a striking latitudinal gradient in multiple sclerosis (MS) prevalence, but exceptions in Mediterranean Europe and northern Scandinavia, and some systematic reviews, have suggested that the gradient may be an artefact. The authors sought to evaluate the association between MS prevalence and latitude by meta-regression.

Methods and findings: Studies were sourced from online databases, reference mining and author referral. Prevalence estimates were age-standardised to the 2009 European population. Analyses were carried out by means of random-effects meta-regression, weighted with the inverse of within-study variance. The authors included 650 prevalence estimates from 321 peer-reviewed studies; 239 were age-standardised, and 159 provided sex-specific data. The authors found a significant positive association (change in prevalence per degree-latitude) between age-standardised prevalence (1.04, p < 0.001) and latitude that diminished at high latitudes. Adjustment for prevalence year strengthened the association with latitude (2.60, p < 0.001). An inverse gradient in the Italian region reversed on adjustment for MS-associated HLA-DRB1 allele distributions. Adjustment for HLA-DRB1 allele frequencies did not appreciably alter the gradient in Europe. Adjustment for some potential sources of bias did not affect the observed associations.

Conclusion: This, the most comprehensive review of MS prevalence to date, has confirmed a statistically significant positive association between MS prevalence and latitude globally. Exceptions to the gradient in the Italian region and northern Scandinavia are likely a result of genetic and behaviouralecultural variations. The persistence of a positive gradient in Europe after adjustment for HLA-DRB1 allele frequencies strongly supports a role for environmental factors which vary with latitude, the most prominent candidates being ultraviolet radiation (UVR)/ vitamin D.

Item Details

Item Type:Refereed Article
Keywords:latitude, multiple sclerosis, vitamin D, ultraviolet radiation, UVR
Research Division:Medical and Health Sciences
Research Group:Public Health and Health Services
Research Field:Epidemiology
Objective Division:Health
Objective Group:Public Health (excl. Specific Population Health)
Objective Field:Preventive Medicine
Author:Simpson Jr, S (Dr Steve Simpson JR)
Author:Blizzard, L (Associate Professor Leigh Blizzard)
Author:Otahal, P (Mr Petr Otahal)
Author:Van der Mei, I (Associate Professor Ingrid van der Mei)
Author:Taylor, B (Professor Bruce Taylor)
ID Code:71067
Year Published:2011
Web of Science® Times Cited:204
Deposited By:Menzies Institute for Medical Research
Deposited On:2011-07-07
Last Modified:2016-09-30
Downloads:12 View Download Statistics

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