# Insulin Resistance and Metabolic Dysfunction in Early-Stage Parkinson’s Disease: Evidence from a Preliminary Case-Control Study

## TL;DR

Early-stage Parkinson’s disease patients show higher insulin resistance compared to healthy individuals, suggesting metabolic dysfunction is part of the disease’s underlying biology.

## Contribution

This study is the first to show elevated insulin resistance in levodopa-naïve PD patients, linking metabolic dysfunction to early PD pathophysiology.

## Key findings

- PD patients had significantly higher fasting insulin and HOMA-IR compared to controls.
- 70% of PD patients met insulin resistance criteria versus 32.5% of controls.
- Results remained significant after adjusting for age, sex, and BMI.

## Abstract

Background: Parkinson’s disease (PD) is increasingly recognized as a multisystem disorder in which metabolic dysfunction may contribute to disease susceptibility and progression. Peripheral insulin resistance (IR) has been implicated in PD, but data in levodopa-naïve patients are currently limited. Objective: To investigate the prevalence of IR and metabolic dysfunction in early-stage, levodopa-naïve PD patients and their association with clinical features. Methods: We conducted an exploratory case–control study including 20 levodopa-naïve PD patients and 40 age-, sex-, and BMI-matched healthy controls. Participants underwent comprehensive clinical and metabolic assessments, including fasting glucose, insulin, lipid profiles, and HOMA-IR calculation. Peripheral IR was defined using HOMA-IR cut-offs of ≥2.0 (primary analysis) and ≥2.5 (sensitivity analysis). ANCOVA adjusted for age, sex, and BMI was used for between-group comparisons. Results: PD patients exhibited higher fasting insulin (10.7 ± 5.2 vs. 8.0 ± 4.4 µIU/mL; p = 0.020) and HOMA-IR (2.63 ± 1.40 vs. 1.89 ± 1.21; p = 0.014) compared to controls. Using a HOMA-IR ≥ 2.0, IR prevalence was 70% in PD vs. 32.5% in controls (OR = 4.85, 95% CI 1.52–15.50, p = 0.012). ANCOVA analysis confirmed group differences after adjusting for covariates (respectively, p = 0.032 for insulin and p = 0.023 for HOMA-IR). A sensitivity analysis excluding six patients receiving dopaminergic therapy further supported the robustness of the results. No significant correlations were observed between IR and disease severity scores. Conclusions: Early-stage, levodopa-naïve PD patients exhibit a higher prevalence of peripheral insulin resistance compared with matched controls. These findings support the hypothesis that metabolic dysfunction is an intrinsic component of PD pathophysiology and may represent a target for early intervention.