Do athletes need fish oil supplements?

In a previous blog we covered what fish oil is and what omega-3 fatty acids are. We also looked at some health claims. Here we look at the potential benefits for athletes. For the evidence on specific uses, see our blogs on does fish oil build muscle? and fish oil and injury.

Why would athletes need fish oil?

Fish oil is one of the most widely used supplements in sport. It is taken to speed up recovery, to reduce inflammation, to protect the brain and to improve performance, and the reasoning is plausible. EPA and DHA are built into the membranes of muscle cells and other tissues, and they influence the signalling molecules that regulate inflammation. More than 100 studies have investigated fish oil supplements in athletes over the past 25 years, but until recently there was no systematic review that collated this evidence and provided a consensus, specifically for elite athletes.

Training itself improves omega-3 status. It increases the content of docosahexaenoic acid (DHA, 22:6n-3) in the membranes of muscle cells (2), and athletes who have trained for years may therefore have less need for fish oil supplements. However, expert groups such as the International Olympic Committee and the American College of Sports Medicine were either “unclear if fish oil supplements should be pursued by athletes” or offered no guidance. The general population is a different case, because in most developed countries intakes of EPA and DHA are low as few people eat oily fish regularly. We therefore performed a systematic review of the existing literature (1).

How was the review done?

We searched PubMed, Embase, Web of Science and Google Scholar up to April 2019 and included only randomised placebo-controlled trials in athletes that measured the effect of fish oil on a health, physiological, biochemical or performance outcome. Of 137 papers identified, 32 met the criteria. The athletes ranged from recreational to elite and from Olympic to professional sports. Their mean age was about 25 years and 70% of the trials were conducted in males. Methodological quality was assessed with the Physiotherapy Evidence Database (PEDro) scale and ranged from 6 to a maximum of 11 points. Only 4 of the 32 trials reported effect sizes.

These numbers set the limits of what can be concluded. With only 4 trials reporting effect sizes, we can say more about whether an effect was seen than about how large it was. And because the athletes were mostly young men, we know much less about women and older athletes.

What did we find?

Fish oil supplements had consistent positive effects on reaction time and mood, on cardiovascular dynamics (in cyclists) and on skeletal muscle recovery. They also attenuated the pro-inflammatory cytokine TNF-alpha and increased post-exercise nitric oxide responses. No clear effects were seen on endurance performance, training adaptations, muscle force or lung function, other than in cases of exercise-induced bronchoconstriction (EIB).

"... fish oil supplements exert consistent positive effects on cognition and mood, cardiovascular dynamics (in cyclists), and muscle recovery".

No benefits for fish oil supplements were seen on endurance exercise performance, training adaptations, muscle force, or lung function

Muscle recovery is the outcome with the most detail in individual studies, and it is discussed in our blog on fish oil and injury. Fish oil on its own did not reduce muscle damage or soreness after hard eccentric exercise in trained young men (3). However, when fish oil was added to a protein-containing supplement for five to six weeks, perceived muscle soreness was lower in football players (4) and likely lower in rugby players (5). In the football study, soreness over 72 hours was less than half with fish oil compared with the protein drink (4). In the rugby study, countermovement jump height increased by 4.6% with omega-3 and decreased by 3.4% with placebo (5). These studies are small and the effects on performance were inconsistent, so the recovery benefit is best described as less perceived soreness.

Are there negative effects of fish oil?

We also looked for evidence of a negative effect of fish oil on performance. Few negative outcomes were reported and the side effects were mild, although we identified one case of a duodenal ulcer associated with a high dose of fish oil. Many of the randomised controlled trials (RCTs) that reported positive effects used doses that can be obtained from oily fish in the diet. A typical 1000 mg fish oil capsule provides only about 300 mg of EPA and DHA combined, so the amount of EPA and DHA on the label is the number that counts. EPA and DHA are natural constituents of seafood, including algae and crustaceans, and are found in much smaller amounts in dairy and meat, where the diet of the animal determines the omega-3 content. Oily fish such as salmon, mackerel, herring, sardines and trout are the richest dietary sources.

The quality of supplements is a second consideration, and it was raised in the scientific literature we reviewed. In a survey of commercial fish oil capsules sold in China, the EPA content met the labelled amount in 64% of products and the DHA content in 48% (6). These data come from one market, but the declared content cannot be taken for granted. Oil exposed to air, light or heat also becomes rancid, so capsules should be stored sealed, in the dark and cool.

Can fish oil protect against concussion?

Before we started the review we had become aware of a growing interest in fish oil as a way to prevent concussion in athletes, and as an addition to medical management after head injuries in military and non-athletic settings (7, 8). Our review found only one RCT in athletes, which reported that DHA lowered a blood marker of neuronal injury in American football players. This is a positive result for DHA, but a marker of injury is not a concussion, and no study has yet investigated whether DHA speeds up recovery from concussion. We also concluded that more research is needed on the effect of fish oil on neuromuscular performance, bone metabolism, rehabilitation from injury (for example surgical compared with non-surgical outcomes, including bone stress), EIB, risk of illness and risk of sudden cardiac death in athletes. The concussion evidence is discussed in more detail in our blog on fish oil and injury.

In that study (9), 81 American football players from a National Collegiate Athletic Association (NCAA) Division I team took 2, 4 or 6 g of DHA per day or a placebo over 189 days of a season. A blood marker of damage to axons increased over the season, and DHA likely attenuated this increase by a small to moderate amount, independent of the dose. Even the lowest dose of 2 g of DHA per day is many times more than a standard fish oil capsule provides.

"RCTs that reported positive effects for [fish oil supplements], used doses that were achievable through the consumption of oily fish in the diet".

What can we do for the athlete now?

First, we should measure omega-3 status. A fatty acid profile gives more objective information on whether an individual athlete would benefit from fish oil, and avoiding a deficiency is paramount. Athletes who follow a vegan diet are at high risk of an inadequate intake of EPA and DHA. Where the athlete is open to such advice, we should also encourage the consumption of dietary sources, because many of the positive trials used doses that oily fish can provide. Second, we should monitor omega-3 status periodically, so that the supplementation regime can be adjusted where necessary. If a supplement is used, the EPA and DHA content per serving should be checked on the label rather than the weight of the oil.

We should firstly measure omega-3 status in order to capture fatty acid profiles that gives us greater objectivity in answering whether a given athlete would benefit from fish oil supplementation

Practical takeaways

1. There is some clear evidence for beneficial effects of fish oil and of eating oily fish in athletes, but not for the main performance outcomes, such as endurance performance and training adaptations.

2. Measuring and monitoring omega-3 status makes the decision to use fish oil supplements more objective.

3. Added to a protein-containing supplement for five to six weeks, fish oil reduced perceived muscle soreness in football and rugby players, but the effects on performance were inconsistent.

4. Many positive trials used doses that oily fish can provide, and the EPA and DHA content on the label is the number that counts.

5. The evidence comes mainly from young men and only 4 of the 32 trials reported effect sizes, so more research is needed, in women and older athletes in particular.

Conclusion

The past 25 years of research have identified several applications of fish oil in athletes, mainly for mood, reaction time, cardiovascular dynamics and muscle recovery. Training itself improves omega-3 status, so athletes who eat oily fish may need less from supplements than is often assumed. Fish oil as a way to protect athletes from the effects of concussion and traumatic brain injury (TBI) is still at an early stage.

References

1. Lewis NA, Daniels D, Calder PC, Castell LM, Pedlar CR. Are there benefits from the use of fish oil supplements in athletes? A systematic review. Adv Nutr 11(5) 1300-1314, 2020.

2. Helge JW, Wu BJ, Willer M, Daugaard JR, Storlien LH, Kiens B. Training affects muscle phospholipid fatty acid composition in humans. J Appl Physiol 90(2) 670-677, 2001.

3. Mackay J, Bowles E, Macgregor LJ, Prokopidis K, Campbell C, Barber E, Galloway SDR, Witard OC. Fish oil supplementation fails to modulate indices of muscle damage and muscle repair during acute recovery from eccentric exercise in trained young males. Eur J Sport Sci 23(8) 1666-1676, 2023.

4. Philpott JD, Donnelly C, Walshe IH, MacKinley EE, Dick J, Galloway SDR, Tipton KD, Witard OC. Adding fish oil to whey protein, leucine, and carbohydrate over a six-week supplementation period attenuates muscle soreness following eccentric exercise in competitive soccer players. Int J Sport Nutr Exerc Metab 28(1) 26-36, 2018.

5. Black KE, Witard OC, Baker D, Healey P, Lewis V, Tavares F, Christensen S, Pease T, Smith B. Adding omega-3 fatty acids to a protein-based supplement during pre-season training results in reduced muscle soreness and the better maintenance of explosive power in professional Rugby Union players. Eur J Sport Sci 18(10) 1357-1367, 2018.

6. Zhou Q, Xu L, Xu Y, Xue Q, Xue C, Jiang X, Wen Y. Systematically investigating the qualities of commercial encapsulated and industrial-grade bulk fish oils in the Chinese market. Foods 14(9) 1623, 2025.

7. Bailes JE, Patel V. The potential for DHA to mitigate mild traumatic brain injury. Mil Med 179(suppl_11) 112-116, 2014.

8. Lewis MD. Concussions, traumatic brain injury, and the innovative use of omega-3s. J Am Coll Nutr 35(5) 469-475, 2016.

9. Oliver JM, Jones MT, Kirk KM, Gable DA, Repshas JT, Johnson TA, Andréasson U, Norgren N, Blennow K, Zetterberg H. Effect of docosahexaenoic acid on a biomarker of head trauma in American football. Med Sci Sports Exerc 48(6) 974-982, 2016.