NEFL and multiple sclerosis: ARR, annual relapse rate; BMD, bone mineral density; BOD, burden of disease; EDSS, expanded disability status scale; FIS, fatigue impact scale; FSS, fatigue severity scale; HADS-D, Hospital Anxiety and Depression Scale – Depression; IL, interleukin; INF-γ, interferon‐gamma; MRI, magnetic resonance imaging; MS, multiple sclerosis; MSFC, multiple sclerosis functional composite; NfL, neurofilament light chain; QoL, quality of life; serum 25(OH), serum 25-hydroxyvitamin D; SI, stimulation index; TGF-β, transforming growth factor-beta; TNF-α, tumor necrosis factor-alpha