Vitamins for Athletes: What Actually Matters, What You’re Wasting Money On, and What Can Hurt You
Table of Contents
Introduction
It is entirely natural for athletes — and patients more broadly — to want to maximise their performance. They invest significant time and effort into optimising every aspect of their training, recovery, and daily routine. Alongside nutrition, vitamins and supplements naturally become an area of interest.
However, more is not always better. In some cases, excessive intake of certain vitamins may be harmful to health rather than beneficial. At the same time, many supplements are simply unnecessary, and true deficiencies are often less common than people assume — especially in those already eating a varied, adequate diet.
This article was written to help athletes take a more targeted and evidence-based approach: to focus on what actually matters, to avoid unnecessary supplementation, and to recognise situations where supplements may be neutral — or in some cases, actively counterproductive.
The Real Problem: Vitamins for Athletes Are Not the Same as Vitamins for Everyone
There is a persistent assumption in sports culture that athletes, because they eat more, eat better. The research disagrees. Micronutrient deficiencies are prevalent within athletic populations, and elevated training loads, restricted energy intake during weight-cutting phases, and limited dietary variety in some sports all contribute to this risk [1]. The vitamins most likely to be deficient in athletes are not always the ones most prominently featured in supplement marketing.
This also means that the standard approach — picking a multivitamin off the shelf because “training is hard on the body” — often misses the actual problem entirely. The smarter approach starts with knowing what your blood work actually shows. If you train hard and haven’t had your micronutrient status checked, preparing properly for a blood test as an athlete is a reasonable first step before spending money on supplements.
Some of the athletes I work with take a “more is better” approach — trying to cover all bases by taking multiple vitamin supplements at once to ensure they are getting everything they might need. However, with the right information, it becomes possible to avoid unnecessary supplementation while focusing on the specific vitamins that are actually lacking.
Vitamins for Athletes: What the Evidence Says You Actually Need
Vitamin D — One of the Most Commonly Documented Deficiencies in Sport
Among all vitamins for athletes, vitamin D has the strongest and most consistent evidence base for genuine deficiency at population level. A systematic review and meta-analysis of 2,313 athletes found that 56% had vitamin D inadequacy, defined as serum 25(OH)D below 32 ng/mL [2]. The risk was significantly higher in winter and spring (RR 1.85; 95% CI 1.27–2.70) and in indoor sports (RR 1.19; 95% CI 1.09–1.30) [2]. The elevated risk at latitudes above 40°N reached significance in a sensitivity analysis when Middle Eastern populations were excluded as outliers [2]. A separate 2022 meta-analysis focused specifically on elite athletes reported a pooled prevalence of vitamin D insufficiency (defined as 25(OH)D <50 nmol/L) of 30% (95% CI 22–39%) [10].
The consequences extend beyond bone health. A 2024 systematic review of randomised controlled trials in elite athletes concluded that the greatest potential benefits of vitamin D supplementation may relate to aerobic endurance, anaerobic power, and strength [3]. A narrative review on vitamin D and athletic injuries found that a 25(OH)D value below 75.8 nmol/L has been identified as a risk factor for stress fractures in athletes [9].
A 2026 narrative review across all major vitamins for athletes confirmed that vitamin D deficiency is highly prevalent, particularly in indoor sports and during winter months, with evidence for musculoskeletal benefit from supplementation [1].
Practical threshold: If you train primarily indoors, live at northern latitudes, or train through winter months, checking your 25(OH)D can be clinically reasonable — these factors recur in the literature as contributors to deficiency risk[2].
At higher latitudes — such as in my home country, Finland — I frequently encounter vitamin D insufficiency in athletes, particularly those who train indoors. Limited sun exposure in these settings makes endogenous vitamin D production unreliable.
Because of this, I often prioritise checking 25(OH)D levels in these athletes. When low levels are identified, targeted supplementation becomes a straightforward and evidence-based intervention, especially during winter.
In situations where testing is not available, a cautious, low-dose supplementation strategy during winter may still be reasonable — but this should be seen as a practical compromise rather than a substitute for proper assessment.
B Vitamins — Critical for Energy, Easy to Miss in Restricted Diets
When discussing vitamins for athletes, B vitamins are often underrated. The B-complex — thiamine (B1), riboflavin (B2), niacin (B3), pantothenic acid (B5), pyridoxine (B6), biotin (B7), folate (B9), and cobalamin (B12) — support energy metabolism and red blood cell synthesis, making adequate intake relevant for athletes undertaking high training loads [1].
Deficiencies tend to occur in specific subgroups rather than across the board. Female endurance athletes and athletes following vegetarian or vegan dietary patterns are among those who may warrant closer monitoring, particularly for B12; folate may also merit attention in some subgroups[1]. For a detailed breakdown of how B12 and folate behave specifically in athletic populations, including the markers worth tracking beyond a standard serum level, see Vitamin B12 and Folate in Athletes: Beyond Anemia Prevention.
A study in 72 recreational endurance athletes found normal serum B12 levels but significantly higher methylmalonic acid (MMA) concentrations compared with inactive controls — a finding the authors interpreted as suggesting altered vitamin B12 metabolism in this population[6]. This is relevant because standard serum B12 testing may not capture the full picture in high-volume training populations. An elevated MCV in athletes, for example, can be an early indicator of B12 or folate insufficiency that would otherwise go unnoticed.
Folate plays an important role in haematological adaptation and cell synthesis, which is one reason it may deserve attention — along with B12 — in certain athletic subgroups such as female endurance athletes[1]. Red cell production is under significant demand in endurance athletes, and markers like reticulocyte count can reflect how well the bone marrow is responding to that demand.
The important nuance: There is moderate evidence that B-vitamin sufficiency supports energy metabolism and recovery. There is, however, low evidence that supplementation improves performance in athletes who are already replete [1]. Correct a deficiency, yes. Take B-complex supplements on top of an already adequate diet? The benefit is unlikely.
In my practice, I do occasionally see vitamin B12 deficiency in physically active patients — particularly in those who are dieting or restricting energy intake. The risk is even more pronounced in athletes following a vegan diet, where no animal-derived sources of B12 are consumed. That said, I encounter B12 deficiency far less frequently than vitamin D insufficiency — it does come up from time to time, but not in a consistent or systematic way.
In these cases, ensuring adequate intake becomes important. For those who avoid animal products entirely, fortified foods or supplementation are often necessary to maintain sufficient B12 levels. When dietary flexibility allows, including some animal-based sources can help support adequate intake, but this is not always feasible for all athletes.
Vitamins for Athletes: What You Are Probably Wasting Money On
Multivitamins in Well-Nourished Athletes
Multivitamin use is common in competitive sport. The evidence for benefit in athletes eating adequately, however, is not. A review in the Journal of the International Society of Sports Nutrition concluded that multivitamin and mineral supplements are unnecessary for athletes or other physically active individuals who are on a well-balanced diet with adequate calories [5]. A separate review confirmed the same position: micronutrient supplementation in well-nourished athletes does not enhance physical performance [7].
This is not an argument against vitamins. It is an argument for testing first. When no deficiency is present, multivitamins have not been shown to provide an ergogenic benefit [5][7]. If a deficiency is present, a targeted supplement addressing that specific shortfall is more rational than a broad-spectrum product.
In practice, a targeted approach is usually more useful than broad multivitamin screening. I tend to prioritise vitamin D — and, in selected cases, B12 or folate — and then supplement based on confirmed deficiencies.
For otherwise healthy athletes consuming a varied mixed diet, most vitamin requirements are typically met through food alone. Vitamin D remains the main exception, particularly at higher latitudes. Iron deficiency is another important consideration, especially in menstruating female athletes.
A basic laboratory panel — including 25(OH)D, vitamin B12, often folate, and iron parameters — usually covers the areas most relevant to athletic populations.
Extensive vitamin panels are rarely needed. When progress stalls, the explanation is more often found in factors such as energy intake, training structure, or recovery — rather than in unidentified deficiencies across multiple vitamins.
Vitamin A Supplementation Without Confirmed Deficiency
Vitamin A contributes to immune regulation, metabolic control, and mitochondrial function [1]. However, athlete-specific clinical trials are minimal and findings inconsistent. The current evidence certainty for direct performance outcomes from vitamin A supplementation is rated as very low, and supplementation cannot be recommended for ergogenic purposes in the absence of a confirmed deficiency [1].
In clinical practice, true vitamin A deficiency is extremely rare. I virtually never encounter it in otherwise healthy patients. By contrast — as discussed in the following section — excessive intake of vitamin A can be harmful in a number of situations, which further limits the rationale for routine supplementation.
What Can Work Against You
This is the section most patients, athletes and coaches have not been told about, and it matters considerably when thinking about vitamins for athletes.
The Antioxidant Trade-Off: Vitamins C and E
The conventional logic around antioxidant vitamins — primarily vitamins C and E — is that hard training generates oxidative stress, antioxidants neutralise oxidative stress, therefore antioxidant supplementation helps athletes recover and adapt. The logic sounds correct. The biology is more complicated.
Reactive oxygen species generated during exercise also function as signalling molecules involved in training adaptation pathways, and high-dose antioxidant supplementation may interfere with those signals. A 2026 narrative review synthesising this evidence concluded that excessive intake of vitamins C and E may impair adaptive responses including mitochondrial biogenesis and protein synthesis [1].
The key human RCT underpinning this concern was a double-blind study from the Norwegian School of Sport Sciences, published in the Journal of Physiology. Fifty-four subjects performed 11 weeks of endurance training while receiving either vitamin C (1,000 mg/day) and vitamin E (235 mg/day) or placebo. The supplemented group showed blunted training-induced increases in the mitochondrial protein COX4 (p ≤ 0.03 between groups). Markers of mitochondrial biogenesis — including mRNA levels of CDC42 and MAPK1 — were also lower in the supplemented group (p ≤ 0.05). Crucially, the study’s authors noted that while cellular adaptations were blunted, this did not translate to detectable differences in VO₂max or running performance within the study’s timeframe, and they called for caution when considering antioxidant supplementation combined with endurance exercise [4].
In practice, this is often counterintuitive. Many patients I see consider vitamin C harmless — a water-soluble vitamin that can be taken freely because excess is excreted. It is also common for patients to increase their intake significantly when they feel they are getting sick, sometimes taking high doses in a “more is better” fashion, not unlike how zinc is often used during illness. This pattern likely reflects, at least in part, the lasting influence of early claims about vitamin C popularised by Linus Pauling.
While this is generally true in terms of safety, it does not mean that more is better in the context of training. The practical implication is that chronic high-dose antioxidant supplementation during hard training blocks may blunt some of the cellular adaptations that training is intended to produce.
At higher doses, antioxidant supplementation may interfere with exercise-induced signalling pathways, potentially blunting some of the adaptations athletes are aiming to develop [4][1]. This effect has been demonstrated at the cellular level in human studies [4]. However, clear negative effects on long-term performance have not been consistently shown, and the practical significance of these findings remains uncertain [4][1].
As with most aspects of nutrition, moderation is key — there is little reason to avoid vitamin C altogether, but routine high-dose supplementation is unlikely to offer additional benefit and may not be optimal in a training context.
Vitamin A at High Doses — Toxicity and Teratogenic Risk
Because vitamin A is fat-soluble, it accumulates in hepatic tissue. Vitamin A toxicity — hypervitaminosis A — can be either acute from a single high dose or chronic from sustained excess intake. Symptoms include nausea, bone pain, and in more severe cases liver damage ranging from steatosis to fibrosis [8]. Vitamin A in particular carries genuine hepatotoxicity risk at chronic excess [8].
Because preformed vitamin A accumulates in the body — particularly in the liver — excessive intake carries a genuine risk of toxicity. Unlike most water-soluble vitamins, this makes vitamin A a poor candidate for empirical, unsupervised supplementation. The risk increases further when multiple overlapping supplements are used, especially products that combine fat-soluble vitamins without clear dose awareness.
Particular caution is required in pregnancy, where excessive intake of preformed vitamin A is associated with teratogenic risk. In addition, certain foods — most notably liver — already contain very high amounts of vitamin A, meaning total intake can rise quickly when dietary sources and supplements are combined.
In my clinical practice, there are very few situations where I would recommend vitamin A supplementation. Outside of specific, targeted indications, routine use is uncommon. More potent vitamin A derivatives, such as systemic retinoids, are used in clinical medicine, but their use is tightly controlled and typically requires specialist supervision and strict pregnancy prevention.
A related issue I often encounter is the routine use of fish oil or cod liver oil supplements. These products typically combine omega-3 fatty acids with fat-soluble vitamins such as A, D, and E, which introduces two potential concerns. First, combining multiple sources can unintentionally increase intake of fat-soluble vitamins — particularly A and E — to levels where accumulation becomes relevant. Second, omega-3 fatty acids have mild antiplatelet effects, which may be clinically relevant in certain contexts.
For this reason, supplement use should be reviewed in patients taking anticoagulant or antiplatelet medications, as well as in those preparing for surgery. In acute situations — such as suspected stroke, where thrombolytic therapy may be considered — awareness of supplement use forms part of the overall bleeding risk assessment.
Conclusion
The question is not whether vitamins matter for athletes — it is how to use them intelligently.
For most athletes, the foundation remains simple: a varied, adequate diet will cover the majority of micronutrient needs. When deficiencies do occur, they tend to follow predictable patterns — vitamin D in northern latitudes and indoor sports, iron in menstruating female athletes, and B12 in those with restricted or plant-based diets. In these situations, targeted identification and correction of deficiencies is both rational and supported by the evidence.
What does not work — and what the supplement industry continues to promote — is the idea that more is better. Broad multivitamin use in already well-nourished athletes offers little benefit, and in some cases, excessive or poorly targeted supplementation may introduce unnecessary risk. This is particularly relevant for fat-soluble vitamins, which accumulate in the body, and for high-dose antioxidant supplementation, where the biological effects are more complex than often assumed.
Perhaps the most important takeaway is this: supplementation should follow assessment, not precede it. A small number of well-chosen laboratory tests can answer most clinically relevant questions, and in many cases, the limiting factor in performance is not a hidden vitamin deficiency, but something more fundamental — energy availability, training structure, or recovery.
In practice, the goal is not to eliminate supplements, but to use them with precision. Test where appropriate. Correct what is actually deficient. Avoid what is unnecessary. And recognise that, in some cases, doing less is not only more rational — it may also be more effective.
References
[1] https://pmc.ncbi.nlm.nih.gov/articles/PMC12845069/
[2] https://pubmed.ncbi.nlm.nih.gov/25277808/
[3] https://pmc.ncbi.nlm.nih.gov/articles/PMC10768611/
[4] https://pmc.ncbi.nlm.nih.gov/articles/PMC4001759/
[5] https://pmc.ncbi.nlm.nih.gov/articles/PMC2129136/
[6] https://pubmed.ncbi.nlm.nih.gov/16286674/
[7] https://pubmed.ncbi.nlm.nih.gov/34662692/
[8] https://pubmed.ncbi.nlm.nih.gov/40901583/
