Serum 25-hydroxyvitamin D3 level may be associated with olfactory dysfunction in de novo Parkinson's disease.

The purpose of our study was to investigate the association between olfactory function in Parkinson's disease (PD) and serum vitamin D status. Thirty-nine patients with de novo PD were enrolled in this study. Olfactory function was assessed by an odor identification test, as a part of the KVSS (Korean version of sniffin' sticks) II test. All patients were also assessed with the NMSS (Non-Motor Symptoms Scale for PD) to check the subjective change in ability to smell. Vitamin D status was determined by measuring the level of serum 25-hydroxyvitamin D3 (25-OHD3). Multiple linear regression tests and correlation analysis were applied to verify the association between serum 25-OHD3 level and patients' subjective and objective olfactory dysfunction. The serum 25-OHD3 level was independently associated with odor identification score in patients with PD (β = 0.38, p < 0.01). Another statistically significant variable was clinical subtype of PD (Intermediate subtype: β = -0.33, p < 0.05; Akinetic rigid type: β = -0.55, p < 0.01). The serum 25-OHD3 level was also negatively correlated with the score for item number 28 in NMSS (Spearman's rho = -0.32, p < 0.05). Our results showed that vitamin D status might be an independent factor for olfactory dysfunction in PD. Although the underlying mechanism has not been clearly identified, we postulate that vitamin D plays a role in the pathogenesis of olfactory dysfunction in PD. Further investigation to elucidate the precise relationship of vitamin D to PD is essential.