A new study used published research from the UK, U.S., Russia and Australia, to estimate and project the proportion of MS incidence that could be attributed to two modifiable multiple sclerosis risk factors: smoking, and childhood and adolescent high BMI. The researchers project childhood and adolescent obesity will contribute up to 14 percent of overall risk of MS in 2035.

Previous studies have estimated that 53 percent of MS risk is directly attributable to environmental factors, and up to one in five MS cases could be attributable to smoking. Smoking and high body mass index are leading global drivers of many noncommunicable diseases and cause significant premature morbidity and mortality.

The study – by Barts Charity and involving researchers from Queen Mary University of London, Barts Health NHS Trust, and the University of Oxford – found that, in 2015, approximately 10 percent of the population risk of MS could be attributed to smoking, but that this will decrease in response to the drop in smoking rates. Conversely, the potential contribution of early life obesity to MS incidence is increasing, because an increasing proportion of the population in the countries studied are obese. While the proportions vary between countries, the same patterns can be seen worldwide.

In 2015, early life high BMI was linked to a higher risk than smoking in the U.S. and Australia, and an equivalent level in the UK. The risk for high early life BMI is highest in the U.S. (11 percent) and estimated to increase to 14 percent by 2035. In the UK, high early life BMI will account for 10 percent of the population risk of MS in 2035.

If these observations are confirmed to be causal, the authors said reducing the prevalence of these modifiable lifestyle risk factors is likely to have an important effect on MS incidence. A limitation of the study is that it is an observational analysis of data and has not determined the probability of direct causation of smoking or high BMI on incidence of MS.

The findings were published in the International Journal of Epidemiology.