Background: Aging induces degenerative processes in the body, contributing to the onset of various age-associated diseases that affect the population. Inadequate dietary habits and low physical activity are major contributors to increased morbidity during aging. This study aimed to investigate the combined effects of omega-3 fatty acid supplementation and physical activity on the markers of oxidative stress and antioxidant defense mechanisms in aged male Wistar rats (23–24 months). Methods: The rats were randomly divided into four experimental groups: a sedentary control (placebo, no exercise), a trained (placebo and moderate-intensity graded aerobic exercise; Ex), and two trained groups supplemented with low (160 mg/kg of body weight; O1 + Ex) and high (320 mg/kg of body weight; O2 + Ex) doses of omega-3 fatty acids. The biochemical and functional parameters related to sarcopenia and the markers of oxidative stress were measured in blood and gastrocnemius muscle. Results: The results demonstrated dose-dependent, synergistic effects of omega-3 fatty acid supplementation and physical activity. The higher dose (320 mg/kg of body weight) improved plasma antioxidant capacity (TEAC, +21.01%, p < 0.01) and GPx activity (+78.05%, p < 0.05) while reducing CAT activity in erythrocytes (−19.92%, p < 0.05), likely as an adaptive stress response. Combined interventions also normalized cholesterol levels, improved the functional parameters of sarcopenia (stride length, +14.82%, p < 0.001), and enhanced antioxidant protection in aged rats. Conclusions: These findings highlight the potential of combining omega-3 fatty acid supplementation and physical activity to counteract aging-related degenerative changes. Further research is needed to elucidate the underlying mechanisms and evaluate the long-term benefits of these strategies in aging populations.

Depressive disorder (DD) in children and adolescents is a growing public health concern with a complex and multifactorial etiology. While most biomarker research has focused on adults, increasing attention is being paid to age-specific molecular mechanisms. This narrative review provides a comprehensive overview of current knowledge on potential biomarkers of DD, including genetic, neurotransmitter, hormonal, inflammatory, lipid, and oxidative stress markers, in youth compared to adult populations. Special emphasis is given to findings from the DEPOXIN project (Molecular basis of depressive disorder in children and adolescents, the influence of omega-3 fatty acids and oxidative stress), a multicenter study investigating biological markers in children and adolescents with DD. The project identified significantly increased oxidative stress markers (8-isoprostanes, advanced oxidation protein products, nitrotyrosine) and decreased antioxidant enzyme activity (glutathione peroxidase). Moreover, HDL (high density lipoproteins) cholesterol and its subfractions were negatively correlated with depression severity. At the same time, thromboxane B2, omega-6/omega-3 fatty acid ratios, and salivary cortisol levels showed strong positive correlations with depressive symptoms and biochemical markers of inflammation. These results suggest a distinct molecular profile of depression in paediatric populations, emphasizing the importance of developmental context in biomarker research. The review aims to synthesize existing evidence, compare findings across age groups, and highlight the need for personalized, age-appropriate strategies in the diagnosis and treatment of depressive disorders.