Antioxidant Capacity of Seminal Plasma and Its Association with Semen Quality and Dietary Antioxidant Intake

Background/Objectives: Male infertility is a growing public health concern, with lifestyle and dietary factors increasingly recognized as contributors to impaired sperm function. Oxidative stress plays a central role in sperm damage, yet the relationship between seminal antioxidant capacity, dietary antioxidant intake and semen quality remains unclear. This study investigated the association between seminal plasma antioxidant status, sperm quality parameters and dietary antioxidant intake, while accounting for key lifestyle factors. Methods: A total of 105 men (18-55 years) undergoing semen analysis were enrolled. Semen parameters were evaluated according to the WHO guidelines. Seminal plasma antioxidant capacity was assessed using the Ferric Reducing Antioxidant Power (FRAP) and DPPH radical scavenging assays. Dietary antioxidant intake was estimated using a validated food frequency questionnaire, and lifestyle factors (smoking, alcohol consumption, physical activity, supplement use) were recorded. Correlations and multivariable regression models were applied to examine associations between antioxidant indices and semen quality. Results: Seminal antioxidant capacity showed wide inter-individual variability (FRAP: 1.6-2171.4 μmol Trolox eq/L; DPPH: 28.5-3093.2 μmol Trolox eq/L). Dietary antioxidant intake demonstrated very weak correlations with semen parameters (r < 0.20). Regression analyses identified smoking and higher body weight as strong negative predictors of sperm concentration, total count and motility, whereas physical activity was positively associated with morphology and progressive motility. FRAP exhibited a mixed association with motility subtypes, while supplement use was positively associated with vitality. Conclusions: Lifestyle factors-particularly smoking, body weight and physical activity-were stronger determinants of semen quality than dietary antioxidant intake or seminal antioxidant indices. These findings highlight the importance of modifiable behaviors in male reproductive health and suggest that improving lifestyle habits may offer greater benefits than dietary antioxidant intake alone.