Is Fish Oil Good for Runners? Omega-3, EPA and DHA Explained
Fish oil doesn't get talked about nearly as much as protein or caffeine in running circles, but it's one of the few supplement categories where the average UK diet is genuinely, measurably short of what's recommended — and that gap doesn't close on its own just because you train regularly. It's easy to assume that a generally healthy, active lifestyle automatically covers every nutritional base, but omega-3 is a specific, well-documented exception.
What EPA and DHA actually are
EPA and DHA are the two long-chain omega-3 fatty acids found in oily fish and fish oil supplements. They're structurally different from the plant-based omega-3 (ALA) found in things like flaxseed and chia seeds, and the two contribute differently to how your body uses them — the conversion rate from plant-based ALA into usable EPA and DHA in the body is notably inefficient, which is why fish oil specifically, rather than a generic "omega" or flaxseed-based blend, is what most of the relevant research focuses on for people who don't eat oily fish regularly.
Why UK runners specifically fall short
British Dietetic Association's omega-3 guidance notes that UK intakes of omega-3 sit below recommended levels for most of the population — and runners eating on the go around training, or relying heavily on convenient carb-focused fuelling (bagels, pasta, gels, sports drinks), are not automatically exempt from that gap just because the rest of their diet is otherwise geared towards performance. Oily fish (mackerel, salmon, sardines) is the main dietary source, and UK consumption of it has historically sat well below public health recommendations.
Why this matters more for endurance athletes specifically
Marathon and half marathon training involves months of repeated, high-volume physical stress — and omega-3s are frequently discussed in the context of supporting the body's normal inflammatory response processes as part of a balanced diet. That's a relevant, if often overlooked, consideration for anyone accumulating serious weekly mileage over a long training block, where the cumulative physical load is genuinely different to someone training casually a couple of times a week.
What to look for in a supplement
The two numbers that actually matter on a label are EPA and DHA content specifically, not just total "fish oil" milligrams — a lot of the fish oil in a cheap capsule isn't EPA or DHA at all, it's other fatty acids that don't carry the same evidence base. Checking the EPA/DHA breakdown, not just the headline fish oil number, is the single most useful thing to do when comparing products, and it's exactly where most standard high-street options fall short.
How RunnerVits compares to a typical high-street fish oil
A standard, widely available 1000mg fish oil capsule on the UK market commonly provides around 300mg of combined EPA and DHA — the rest of that 1000mg is made up of other fatty acids that don't carry the same evidence base for heart, brain or recovery support. Even many "extra strength" branded options, sold at a higher price specifically for being more concentrated, tend to land somewhere in the 400-450mg combined EPA/DHA range per capsule.
RunnerVits' High-Strength Omega-3 provides 2,000mg of fish oil per two-capsule serving, including 1,000mg EPA and 500mg DHA — 1,500mg combined EPA and DHA per serving, or 750mg per capsule. That's roughly two-and-a-half times the concentration of a standard 1000mg high-street capsule, and still meaningfully ahead of most premium "extra strength" alternatives, gram for gram. Alongside that strength, it includes Vitamin E to help maintain freshness — fish oil is prone to oxidation, which is part of why quality and concentration both matter, not just the headline number on the front of the tub.
Quick answers
How long does it take to notice a difference?
Omega-3 is a background, cumulative supplement rather than something with an immediate, noticeable effect — most guidance frames it as a daily habit built up over weeks and months, not a same-day performance aid.
Is fish oil safe to take alongside other supplements like creatine or joint support?
Yes — omega-3, creatine, electrolytes and joint support ingredients work through entirely different pathways and are commonly used together as part of a broader daily supplement routine.