Objective:

To investigate the relationship between serum 25-hydroxyvitamin D levels and the risk and severity of distal symmetric polyneuropathy (DSPN) in individuals with type 2 diabetes mellitus (T2DM).

Approach:

• Study Design: A multicenter cross-sectional study involving 569 adults with T2DM from four hospitals in Fujian Province, China, conducted between June 2022 and May 2023.
• Measurement Techniques: Serum 25(OH)D2, 25(OH)D3, and total 25(OH)D levels were measured using liquid chromatography-tandem mass spectrometry (LC-MS/MS).
• Assessment of DSPN: DSPN and its severity were evaluated using a standardized five-item neurological examination and the Michigan Neuropathy Screening Instrument (MNSI).
• Statistical Analysis: Multivariable logistic regression was used to analyze the relationship between 25(OH)D and DSPN, with propensity score matching (PSM) and restricted cubic splines (RCS) for dose-response curve construction.

Key Findings:

• Individuals with DSPN had significantly lower concentrations of 25(OH)D compared to non-DSPN individuals (23.95 ± 5.14 vs. 32.31 ± 5.97 ng/mL, P < 0.001).
• A significant downward trend in the risk of DSPN was observed with increasing 25(OH)D levels (P for trend < 0.001).
• The severity of DSPN increased significantly when 25(OH)D levels dropped below 26.1 ng/mL.

Interpretation:

25(OH)D levels are inversely associated with the risk of DSPN and exhibit a nonlinear relationship with neuropathy severity.

Limitations:

• The study is cross-sectional, limiting causal inferences.
• The sample was limited to individuals from a specific geographic region, which may affect generalizability.

Conclusion:

25(OH)D levels are associated with DSPN risk and severity.