Abstract
OBJECTIVE: The prevalence of multiple sclerosis (MS) varies with latitude: it increases with distance from the equator in both hemispheres. To seek evidence on whether solar radiation is a protective factor for MS, this study investigated whether skin cancer, as an indicator of solar radiation, is less common in people with MS than in others. DESIGN: Analysis of a database of linked hospital records and death certificates. SETTING: The Oxford Region of the National Health Service, England. SUBJECTS: A cohort comprising all people in the database with MS, and comparison cohorts of people with other diseases. RESULTS: Skin cancer was significantly less common in people with MS than in the main comparison cohort (rate ratio 0.49; 95% confidence interval 0.24 to 0.91). There was no general deficit of cancer in the MS cohort, and no deficit of skin cancer in cohorts of people with other autoimmune or neurological diseases. CONCLUSION: The findings support the hypothesis that solar radiation may have a protective influence on the development of MS.