Birth Cohort Effects in Multiple Sclerosis

PURPOSE: To identify potential birth cohort effects in multiple sclerosis in Sweden and particularly in Stockholm county. METHODS: Data on multiple causes of death from multiple sclerosis during 1962 to 1995 in Sweden and 1968 to 1995 in Stockholm county were analyzed using age-period-cohort models and curvature. RESULTS: Mortality from multiple sclerosis was higher in Sweden than in Stockholm county, with stable time trends, slight period effects and marked age effects. Cohorts born before or after a central period, from 1910 through 1930, registered lower mortality. A periodic wave-form mortality pattern was identified, following a 5-to-6-year cycle for cohorts born before 1925 both in and outside Stockholm county, and changing to longer or irregular cycles for cohorts born after 1930. CONCLUSIONS: Although methodological constraints inducing the saw-tooth pattern cannot be excluded, these results are consistent with etiologic hypotheses claiming a role for environmental factors in multiple sclerosis.