Plasma Malondialdehyde Reference Interval and Its Associations with Lifestyle Risk Factors in Thai Undergraduate Students: A Single-Center Cross-Sectional Study

Background/Objectives: Oxidative stress and low-grade chronic inflammation are implicated in the early pathogenesis of non-communicable diseases (NCDs). Malondialdehyde (MDA), a biomarker of lipid peroxidation, may reflect subclinical oxidative stress in apparently healthy young adults. This study aimed to establish a population-specific reference interval for plasma MDA in healthy Thai undergraduate students and evaluate associations with lifestyle risk factors. Methods: This cross-sectional study enrolled 141 Thai college students aged 18–27 years. Plasma MDA was measured using the thiobarbituric acid reactive substances (TBARS) assay. A reference interval was determined non-parametrically (P2.5–P97.5) following IFCC recommendations in a reference subgroup (n = 94). The 75th percentile (P75) was used as an exploratory cutoff for elevated MDA. Associations between MDA and lifestyle risk factors were assessed using logistic regression and multiple linear regression. Results: The plasma MDA reference interval was 1.16–9.23 µmol/L, with P75 = 6.07 µmol/L. Using this cutoff, 25.5% of participants had elevated MDA. High sugar intake was associated with elevated MDA in the P75-based model (adjusted OR = 3.42; 95% CI: 1.08–10.87; p = 0.036). In the linear regression model, BMI emerged as independently associated with MDA (p = 0.004). Conclusions: This study established the first population-specific plasma MDA reference interval for Thai young adults. High sugar intake and BMI emerged as complementary exploratory associations with elevated lipid peroxidation across different models. These findings support plasma MDA as a practical, cost-effective candidate biomarker, providing a basis for further early oxidative stress surveillance and NCD prevention in young populations.