Four months of DHA and whey protein supplementation in semi-professional female soccer players: a prospective non-randomized controlled study of omega-3 status, hematological outcomes, and physical performance

Introduction: Omega-3 polyunsaturated fatty acids (n-3 PUFAs) are well established in cardiovascular and cognitive health, yet their role in athletic performance remains insufficiently characterized. Mechanistic links have been proposed via erythrocyte membrane remodeling, blood rheology, and inflammatory modulation. Female athletes represent a particularly relevant but underexplored population, given the potential dual benefits for performance and menstrual health. This study aimed to determine whether long-term DHA plus whey protein supplementation improves erythrocyte omega-3 status, modulates hematological markers relevant to oxygen transport, and translates to performance or menstrual symptom benefits in female athletes. Menstrual symptoms and hormonal profiles were examined as exploratory secondary outcomes.

Methods: In this prospective non-randomized controlled trial, 38 semi-professional female soccer players were assigned to either an encapsulated algae-based docosahexaenoic acid (DHA) intervention (1000 mg/day + whey protein; n = 20) or reference group ( n = 18) over four months. Assessments were conducted pre-, mid- (2 months), and post-intervention, including blood analyses HS-Omega-3 Index (HS-O3I), lipophilic index (LI), hematology, cytokines and football-specific performance tests with menstrual cycle phase monitored and testing scheduled to account for hormonal fluctuations.

Results: Baseline omega-3 status was suboptimal (HS-O3I: 5.08 ± 1.26%). DHA supplementation significantly increased the HS-O3I at Mid (6.36 ± 2.21%, p < 0.001) and Post (6.8 ± 2.7%, p < 0.001), with a large Group × Time interaction (ηp 2 = 0.72). LI showed transient remodeling, with increases at Mid and partial normalization by Post. Hematological analyses revealed higher mean corpuscular volume (MCV) and reticulocyte hemoglobin in the intervention group, although baseline differences cannot be excluded. MPO concentrations declined over time ( p < 0.05). No significant group differences occurred in sprint, jump, or individual anaerobic threshold (IAS) however, higher Post HS-O3I was associated with higher IAS (unadjusted R 2 = 0.36, p < 0.05). Hormonal profile and premenstrual symptoms did not differ between groups.

Discussion: Four months of DHA plus whey protein supplementation improved erythrocyte omega-3 status and may induce structural membrane changes. The association between higher HS-O3I and aerobic capacity might suggest a functional link between omega-3 status and endurance efficiency in female athletes, which still requires further confirmation.