Estimated and projected burden of multiple sclerosis attributable to smoking and childhood and adolescent high body-mass index: a comparative risk assessment.
Int J Epidemiol
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BACKGROUND: Smoking and childhood and adolescent high body-mass index (BMI) are leading lifestyle-related risk factors of global premature morbidity and mortality, and have been associated with an increased risk of developing multiple sclerosis (MS). This study aims to estimate and project the proportion of MS incidence that could be prevented with elimination of these risk factors. METHODS: Prevalence estimates of high BMI during childhood/adolescence and smoking in early adulthood, and relative risks of MS, were obtained from published literature. A time-lag of 10 years was assumed between smoking in early adulthood and MS incidence, and a time-lag of 20 years was assumed between childhood/adolescent high BMI and MS incidence. The MS population attributable fractions (PAFs) of smoking and high BMI were estimated as individual and combined risk factors, by age, country and sex in 2015, 2025 and 2035 where feasible. RESULTS: The combined estimated PAFs for smoking and high BMI in 2015 were 14, 11, 12 and 12% for the UK, USA, Russia and Australia in a conservative estimate, and 21, 20, 19 and 16% in an independent estimate, respectively. Estimates for smoking are declining over time, whereas estimates for high early life BMI are rising. The PAF for high early life BMI is highest in the USA and is estimated to increase to 14% by 2035. CONCLUSIONS: Assuming causality, there is the potential to substantially reduce MS incidence with the elimination of lifestyle-related modifiable risk factors, which are the target of global public health prevention strategies.