Background: Previous cross-sectional studies have shown that Parkinson’s disease (PD) patients have lower serum 25-hydroxy vitamin D (25(OH)D) concentrations than controls. Vitamin D deficiency was associated with increased disease severity and cognitive impairment in prevalent PD patients.

Objective: The aim of the study was to determine 25(OH)D in newly diagnosed PD and age-matched controls and to assess if there was an association with clinical outcomes (disease severity, cognition and falls) over the 36-month follow up period.

Methods: A prospective observational study of newly diagnosed PD patients in the North East of England with age-matched controls (PD, n = 145; control, n = 94). Serum 25(OH)D was assessed at baseline and 18 months. Participants underwent clinical assessment at baseline, 18 and 36 months. One hundred and ten participants with PD also took part in a prospective falls study.

Results: Mean serum 25(OH)D concentrations were lower in PD than control participants at baseline (44.1±21.7 vs. 52.2±22.1 nmol/L, p < 0.05) and 18 months (44.2±23.6 vs. 55.7±28.8 nmol/L, p < 0.05). Baseline serum 25(OH)D concentration, age, motor score and dosage of dopaminergic medication were significant predictors of variance of motor severity at 36 months ((ΔR2 = 0.039, F = 6.6, p < 0.01). Serum 25(OH)D was not associated with cognition or falls during the follow up period.

Conclusions: Patients with incident PD had significantly lower serum 25(OH)D concentrations than age-matched controls, which may have implications in terms of bone health and fracture risk. There was a small but significant association between vitamin D status at baseline and disease motor severity at 36 months.