Candidate Biological Indicators of Occupational Stress in Healthcare Workers: Heart Rate, Free Triiodothyronine and HDL Cholesterol—A Cross-Sectional Study

Background/Objectives: Healthcare staff, especially nurses, face high occupational stress, yet objective biological indicators that complement self-report are not well established. We examined whether metabolic, hormonal and physiological markers act as indicators of stress and relate to anxiety, depression and burnout in nurses and other healthcare workers. Methods: We conducted a cross-sectional study of 300 hospital employees (239 in healthcare, of whom 123 were nurses; 61 non-healthcare) at a Croatian university hospital; of 329 completed questionnaires, 300 (91.2%) met the inclusion criteria and were analysed. Fasting glucose, lipids, thyroid hormones, cortisol, heart rate and blood pressure were measured; psychological status was measured using the 42-item Depression Anxiety Stress Scales (DASS-42), Maslach Burnout Inventory and Zung scale. Analyses used Mann–Whitney and Kruskal–Wallis tests, Spearman correlation, hierarchical logistic regression adjusted for age, sex, smoking and thyroid medication use, and receiver operating characteristic (ROC) analysis. Results: Healthcare workers had more favourable glucose, total and low-density lipoprotein (LDL) cholesterol than the older non-healthcare group (all p ≤ 0.003); because the groups differed substantially in age, these unadjusted differences are descriptive only. Metabolic markers correlated only weakly with distress and burnout. Within healthcare workers, elevated stress was discriminated in univariable analysis by low high-density lipoprotein (HDL) cholesterol (area under the curve (AUC) 0.72), raised triglycerides (AUC 0.67) and glucose (AUC 0.66); however, after adjustment for age, sex, smoking and thyroid medication use, none of the markers remained independently associated with elevated stress. Conclusions: In this relatively healthy hospital workforce, routinely available biological markers showed limited value as standalone indicators of occupational stress; they are exploratory rather than validated biomarkers, and require confirmation in larger, prospective, multicentre studies before they can complement—rather than replace—psychological screening in occupational-health practice.