Fatty fish, which include mackerel, herring, salmon and sardines, and certain species of algae (e.g., Schizochytrium sp., Crytthecodiniumcohnii and Phaeodactylumtricornutum) are the only naturally rich sources of the omega-3 polyunsaturated fatty acids (n-3 PUFAs) eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA). EPA and DHA are the most biologically active members of the n-3 PUFA family. Limited dietary sources and fluctuating content of EPA and DHA in fish raise concerns about the status of EPA and DHA among athletes, as confirmed in a number of studies. The beneficial effects of EPA and DHA include controlling inflammation, supporting nervous system function, maintaining muscle mass after injury and improving training adaptation. Due to their inadequate intake and beneficial health-promoting effects, athletes might wish to consider using supplements that provide EPA and DHA. Here, we provide an overview of the effects of EPA and DHA that are relevant to athletes and discuss the pros and cons of supplements as a source of EPA and DHA for athletes.

Purpose: This study aimed to investigate the effects of 12 wk of omega-3 fatty acid supplementation during endurance training on omega-3 index (O3I) and indicators of running performance in amateur long-distance runners. Methods: Twenty-six amateur male long-distance runners ≥29 yr old supplemented omega-3 fatty acid capsules (OMEGA group, n = 14; 2234 mg of eicosapentaenoic acid and 916 mg of docosahexaenoic acid daily) or medium-chain triglycerides capsules as placebo (medium-chain triglyceride [MCT] group, n = 12; 4000 mg of MCT daily) during 12 wk of endurance training. Before and after intervention, blood samples were collected for O3I assessment, and an incremental test to exhaustion and a 1500-m run trial were performed. Results: O3I was significantly increased in the OMEGA group (from 5.8% to 11.6%, P < 0.0001). A significant increase in V̇O_2peak was observed in the OMEGA group (from 53.6 ± 4.4 to 56.0 ± 3.7 mL·kg⁻¹⋅min⁻¹, P = 0.0219) without such change in MCT group (from 54.7 ± 6.8 to 56.4 ± 5.9 mL·kg⁻¹⋅min⁻¹, P = 0.1308). A positive correlation between the change in O3I and the change in running economy was observed when data of participants from both groups were combined (−0.1808 ± 1.917, P = 0.0020), without such an effect in OMEGA group alone (P = 0.1741). No effect of omega-3 supplementation on 1500-m run results was observed. Conclusions: Twelve weeks of omega-3 fatty acid supplementation at a dose of 2234 mg of eicosapentaenoic acid and 916 mg of docosahexaenoic acid daily during endurance training resulted in the improvement of O3I and running economy and increased V̇O_2peak without improvement in the 1500-m run trial time in amateur runners.

Omega-3 polyunsaturated fatty acids (n-3 PUFAs), specifically the most biologically active (eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA)), have well-documented health-promoting effects, including, but not limited to, controlling inflammatory processes in the human body and supporting cardiovascular and cognitive health and visual processes. There is also some evidence pointing to the potential of EPA and DHA to preserve and/or enhance muscle strength. Muscle strength plays a crucial role in preventing age-related decline in skeletal muscle mass and function and the subsequent impaired functionality in the daily lives of the elderly. It also has a significant role in physical performance by aiding in the effectiveness of training elements, such as vertical jumps, sprinting, changes of direction, rate of force development, and anaerobic conditioning. Previous studies have indicated that supplementation with n-3 PUFAs may have a small but significant effect on preserving and/or increasing muscle strength in both healthy adults and in elderly. However, the number of studies published on this topic is limited. The goal of this narrative review is to summarize the effects of EPA and DHA supplementation on muscle strength and identify the limitations of previous studies that, if addressed, will help confirm or exclude the beneficial effects of n-3 PUFAs on muscle strength in humans.

The effects of long-term omega-3 polyunsaturated fatty acid (n-3 PUFA) supplementation during endurance training on tryptophan (Trp) metabolism and mental state of healthy individuals have not been evaluated so far. Concentrations of plasma Trp, its metabolites and IL-6 were assessed in 26 male runners before and after a 12-week training program combined with supplementation of n-3 PUFAs (O-3 + TRAIN group) or medium chain triglycerides (MCTs; TRAIN group). After the 12-week program participants' mood before and after stress induction was also assessed. The effects of the same supplementation protocol were evaluated also in 14 inactive subjects (O-3 + SEDEN group). Concentrations of 3-hydroxykynurenine (3-HK) and picolinic acid (PA) significantly increased only in the O-3 + TRAIN group (p = 0.01; $${\eta }_{p}^{2}$$η p 2 = 0.22 and p = 0.01; $${\eta }_{p }^{2}$$η p 2 = 0.26). Favorable, but not statistically significant changes in the concentrations of kynurenic acid (KYNA) (p = 0.06; $${\eta }_{p }^{2}$$η p 2 = 0.14), xanthurenic acid (XA) (p = 0.07; $${\eta }_{p }^{2}$$η p 2 = 0.13) and 3-hydroxyanthranilic acid (3-HAA) (p = 0.06; $${\eta }_{p }^{2}$$η p 2 = 0.15) and in the ratio of neurotoxic to neuroprotective metabolites were seen also only in the O-3 + TRAIN group. No changes in mood and IL-6 concentrations were observed in either group. Supplementation with n-3 PUFAs during endurance training has beneficial effects on Trp's neuroprotective metabolites.Trial registry: This study was registered at ClinicalTrials.gov with identifier NCT05520437 (14/07/2021 first trial registration and 2018/31/N/NZ7/02962 second trial registration).

Background: Vitamin D plays pleiotropic roles in the body and hence, changes in its metabolism and distribution during starvation could play an important role in the adaptive response to famine. We aimed to identify the responses of some vitamin D metabolites to 8 d of fasting and exercise. Methods: A repeated-measures design was implemented, in which 14 male volunteers fasted for 8 d and performed an exercise test before and after fasting. Serum samples were collected on day 1 after night fasting and after 8 d of complete food restriction, before and 1 h and 3 h after exercise. Results: After 8 d of fasting, compared with baseline values, serum 24,25(OH)₂D₃ and 3-epi-25(OH)D₃ levels significantly increased; those of 25(OH)D₃ and 1,25(OH)₂D₃ were unaffected; and those of 25(OH)D₂ decreased. Exercise on the first day of fasting induced an increase in serum 3-epi-25(OH)D₃ levels, while exercise performed after 8 d of fasting induced an increase in 25(OH)D₃, 24,25(OH)₂D₃, 25(OH)D₂, and 3-epi-25(OH)D₃ levels. Conclusion: Increases in 24,25(OH)₂D₃ and 3-epi-25(OH)D₃ levels imply that fasting stimulates vitamin D metabolism. The effects of exercise on serum vitamin D metabolites, which are most pronounced after fasting and in subjects with serum 25(OH)D₃ above 25 ng/mL, support the notion that fasting and exercise augment vitamin D metabolism.

Alterations in iron metabolism after physical activity are manifested through the rise of blood hepcidin (Hpc) levels. However, in many athletes, no changes in Hpc levels are observed after exercise despite the presence of inflammation. The missing links could be erythropoietin (EPO) and erythroferrone (ERFE), which down-regulate Hpc biosynthesis. EPO, ERFE and Hpc biosynthesis is modified by serum iron through transferrin receptor 2. Consequently, we investigated whether marathon-induced changes in EPO, ERFE and Hpc levels are blood iron-dependent. Twenty-nine healthy male marathon runners were analyzed. Serum iron, ferritin, transferrin, EPO, ERFE and Hpc levels were assessed before, immediately after, and 9 ± 2 days after the marathon. The runners whose serum Hpc decreased after the marathon (n = 15), showed a significant increase in ERFE levels. In athletes whose serum iron levels were below 105 µg/day (n = 15), serum EPO (p = 0.00) and ERFE levels (p = 0.00) increased with no changes in Hpc concentration. However, in athletes with low serum iron, no changes in EPO levels were observed when serum ferritin exceeded 70 ng/mL (n = 7). Conversely, an increase in ERFE levels was observed in marathoners with low serum iron, independently of serum ferritin (n = 7). This indicates modulation of blood iron may affect exercise-induced changes in the EPO/ERFE/Hpc axis. Further study is needed to fully understand the physiological meaning of the interdependence between iron and the EPO/ERFE/Hpc axis.