Vitamin D sufficiency is associated with better inflammatory outcomes in multiple sclerosis (MS). We hypothesize that it is also associated with better long-term neurodegenerative measures.

To show that vitamin D sufficient patients (25-hydroxy vitamin D (25(OH)D) > 80 nmol/L) have better optical coherence tomography (OCT) neuroaxonal measures of ganglion cell layer (GCL) and retinal nerve fiber layer (RNFL) thickness after optic neuritis.

In this prospective cohort study, acute optic neuritis patients underwent OCT and serum 25(OH)D assessments at baseline and at month 6, with comparisons between vitamin D sufficient and insufficient patients, and men and women. Potential confounding variables were evaluated.

Of 49 enrolled, 36 had complete, analyzable data. At baseline, vitamin D insufficiency was associated with greater RNFL thickness (134.3 vs. 95.2 µm; p = 0.003) in affected eyes. At month 6, insufficient patients had greater GCL thinning (GCL inter-eye difference: 14.2 vs. 4.0 µm, p = 0.008). Men had greater RNFL and GCL thinning than women (GCL: 61.2 vs. 69.6 µm, p = 0.036).

Acutely, in optic neuritis, RNFL thickness is increased with vitamin D insufficiency. Chronically, neuronal, and possibly axonal loss are associated with vitamin D insufficiency and male gender, suggesting vitamin D and female gender may confer neuroprotection in optic neuritis, and possibly, central nervous system (CNS) inflammatory disease.