BACKGROUND: Circulating insulin-like growth factor 1 (IGF-1) is positively associated with the risks of certain neurological disorders, including stroke, Alzheimer's disease, and Parkinson's disease. However, the association of IGF-1 with the risk of multiple sclerosis (MS) remains unclear. METHODS: A total of 348,324 participants at baseline were included from the UK biobank in this prospective study. The association of circulating IGF-1 level with MS was analyzed by Cox proportional hazard models. Further, subgroup analyses were conducted to investigate the variables influencing these associations. RESULTS: Among 348,324 individuals, lower circulating IGF-1 concentrations were associated with a reduced risk of MS (95 % CI, 0.5930-0.9700
P value = 0.02763). The association between lower IGF-1 levels and reduced risk of MS remains robust in older and female participants. Moreover, risk of MS appeared to be lower in IGF-1-low individuals who never smoked, currently drinking alcohol, with higher body mass index, and higher glucose concentrations. CONCLUSION: Our findings indicate that a lower concentration of serum IGF-1 was associated with a reduced risk of MS. The results provide evidence that the circulating IGF-1 may play a significant role in the pathogenesis of MS.