Diet quality is not associated with late-onset multiple sclerosis risk- A Danish Cohort Study

Background: Multiple sclerosis (MS) onset is commonly observed in adults aged 20-50 years of age. The incidence rate of MS-onset after age 50, late-onset MS, has increased along with the observed overall increase in MS incidence rate in the past 60 years. In general, the aetiology of MS is largely acknowledged to involve a complex interrelation of environmental and modifiable lifestyle risk factors in genetically susceptible individuals. Smoking is an established risk factor, while the role of the diet in the aetiology of MS remains inconclusive. However, even less is known about the role of diet and smoking in the aetiology of late-onset MS as this subgroup of patients has not gained much attention in the scientific literature. Therefore, the objective of this study was to investigate the association between diet quality and the hazards of late-onset MS diagnosis in relation to smoking habits, thus attempting to identify high-risk individuals. Methods: The study was a prospective cohort study based on the Danish cohort Diet, Cancer and Health including middle-aged individuals (50-64 years) born and residing in Denmark. Cox' proportional hazards models were used to estimate the hazard ratios (HR) for tertiles of diet quality, assessed by means of the Alternative Healthy Eating Index-2010. Information on time-at-risk and diagnosis of MS was collected based on linked information from the Danish Civil Registration System and Danish National Patient Registry. Additionally, a stratified analysis according to smoking status (current smokers, former smokers and never smokers) was conducted while adjusting for sex. Results: A total of 56,867 individuals were followed for a median of 20.4 years. During follow-up, 124 individuals were diagnosed with late-onset MS. No statistically significant association was found between diet quality at baseline and the hazard of MS diagnosis in adjusted analyses (HR highest vs lowest diet quality tertile: 0.79; 95%CI: 0.49-1.27, Test for trend: p = 0.22). Smoking status did not modify the association. Conclusion: In this cohort of middle-aged Danes, diet quality was neither statistically significantly associated with the hazards of late-onset MS diagnosis in the entire sample, nor in sub-groups of current smokers, former smokers or never smokers.