Evaluation of thyroid function and oxidative status on the severity of community-acquired pneumonia

Background Community-acquired pneumonia (CAP) remains a major cause of morbidity and mortality worldwide. Increasing evidence suggests that endocrine dysfunction, oxidative stress, and micronutrient imbalance may influence disease severity and outcomes. Aim To evaluate the relationships between thyroid function, vitamin D status, inflammatory markers and total antioxidant capacity in patients with CAP stratified according to disease severity. Methods This cross-sectional study included 147 patients diagnosed with community-acquired pneumonia in Iraq. Patients were clinically classified into mild and severe CAP groups by physician assessment based on clinical presentation, respiratory compromise, and overall clinical evaluation. Serum levels of thyroid-stimulating hormone (TSH), thyroxine (T4), vitamin D3, total antioxidant capacity (TAC), C-reactive protein (CRP), body mass index (BMI), and age were recorded. CRP was measured as part of routine laboratory assessment using an automated immunoturbidimetric assay. Statistical analysis included descriptive statistics and Pearson correlation analysis stratified by disease severity. Significance was set at p < 0.05. Results TSH was significantly lower in severe cases (0.89 ± 0.4 µIU/mL) compared to mild cases (1.4 ± 0.76 µIU/mL; p < 0.001), while T4 did not differ significantly between groups (7.5 ± 1.9 vs. 8.1 ± 1.6 ng/dL; p > 0.05). Vitamin D3 was significantly lower in severe cases (20.1 ± 6.9 ng/mL) than in mild cases (27.4 ± 9.3 ng/mL; p < 0.01). TAC did not differ significantly between severe (2410 ± 351 µmol/L) and mild (2508 ± 287 µmol/L) cases ( p > 0.05). Zinc also did not differ significantly (83.3 ± 23.3 vs. 84.3 ± 19.7 µg/dL; p > 0.05). In severe cases, CRP showed a very weak positive correlation with vitamin D ( r = 0.16, p = 0.049), a very weak negative correlation with TAC ( r = − 0.11, p = 0.201), and a very weak negative correlation with BMI ( r = − 0.10, p = 0.239). Correlation coefficients were generally weak (all |r| < 0.35). Conclusion Disease severity in CAP is associated with progressive disruption of endocrine and oxidative homeostasis. Interactions between thyroid function, vitamin D status, inflammation, and antioxidant defenses may serve as useful biochemical indicators of disease severity and progression. However, the cross-sectional design precludes causal inference, and the mechanisms underlying these associations remain to be elucidated. Clinical trial registration Clinical trial number: Not applicable.