9 supplements for athletes: what works and what your blood shows

The shelf is full, your feed is full, and almost none of it does what it promises. The honest truth about supplements for athletes is simple: a small group works demonstrably, a second group only works if you have a deficiency, and the rest mostly costs money. This list covers nine supplements, sorted by how strong the evidence is, each with the blood value that tells you whether it adds anything for you.

That last part is where most lists stop and we begin.

A supplement list can tell you vitamin D is "good for recovery". It cannot tell you whether your vitamin D is low. Only a measurement can do that. And it is exactly with the situational supplements that this is the difference between a useful addition and expensive urine.

How we graded these supplements

We looked at three things: the quality of the evidence, whether it adds anything on top of good nutrition, and whether a blood value tells you if you need it. A supplement with strong studies behind it ranks above one that is mainly popular on forums.

Nutrition remains the base. A supplement is called a supplement for a reason: it fills a gap you cannot close with food, nothing more. The full approach to eating around your training sits in nutrition for muscle growth.

The nine below fall into three groups: strong evidence, situational, and overrated.

Supplements with strong evidence

These four have the most and best studies behind them. They work for almost every athlete, regardless of your blood values, because they do not correct a deficiency but directly affect a performance or recovery.

1. Creatine monohydrate

Creatine is the most researched sports supplement there is. The position stand of the International Society of Sports Nutrition concludes that creatine monohydrate is safe and effective for strength and explosive power (PMID 28615996). A dose of 3 to 5 grams per day is enough, every day, and the timing does not matter.

There is one blood value to know before you get a fright.

Creatine raises your creatinine slightly, and that is not kidney damage but a measurement artefact of the supplement itself. What creatine does and does not do to your blood sits in creatine and your blood values.

2. Protein (whey or plant-based)

Protein powder is no miracle, but it works. A meta-analysis of 49 studies showed that extra protein increases strength and muscle gains on top of resistance training, with the largest effect in people who have trained for a while (PMID 28698222). A daily intake of 1.6 to 2.2 grams per kilo of body weight is the guideline.

If you already get that from food, a scoop of powder adds little.

Powder is convenient, not magic: it is simply a fast way to hit your daily target. How much you actually need and why, you work out in how much protein per day.

3. Caffeine

Caffeine is one of the best-supported performance enhancers. The ISSN position stand describes that 3 to 6 milligrams per kilo of body weight, about an hour before exertion, measurably improves endurance, strength and focus (PMID 33388079). For someone of 80 kilos that is roughly 240 to 480 milligrams.

The trap is not the effect, but the timing.

Train late and that same caffeine wrecks your sleep, and sleep is where your recovery happens. Dosing and timing without ruining your night sit in caffeine and pre-workout.

4. Beta-alanine

Beta-alanine helps with efforts lasting one to four minutes that burn hard, such as a heavy set or a short sprint. A meta-analysis of 40 studies found a small but real effect on exercise capacity (PMID 27797728). The dose is 3.2 to 6.4 grams per day, built up over several weeks.

One side effect scares people off unnecessarily.

You can get a tingling on your skin, and that is harmless and passes on its own. It says nothing about how well it works.

Situational: measure first, then supplement

These four only work if you take in too little of them. At a normal value, supplementing adds nothing demonstrable, and with iron, blind supplementing can even be harmful. This is exactly the group where a blood measurement is the difference between worthwhile and wasteful.

5. Vitamin D

Vitamin D is worthwhile if you have a deficiency, and in the Dutch winter that is surprisingly common. The Gezondheidsraad (the Dutch Health Council) advises supplementation for certain groups, precisely because the sun here is too weak for half the year. Whether you fall into that group depends on your value.

That value is called 25-OH vitamin D, and you have it measured.

Supplementing without a deficiency does not demonstrably improve your performance, so this is not one to take by default. What a deficiency does to your recovery, performance and testosterone sits in vitamin D deficiency in athletes.

6. Iron

Iron is the most dangerous on the list to take blind. A deficiency mainly occurs in endurance athletes and in women, and it hits your endurance hard (PMID 31055680). But too much iron accumulates and is harmful, so this is not a supplement you take on a guess.

The value you measure for this is ferritin, your iron store.

Take two endurance athletes with the same fatigue: one has a ferritin of 15, the other 90. Only the first benefits from iron, and from the outside you cannot see that difference. Without measuring, they would both buy the same tub.

Supplement only with a confirmed deficiency and preferably under the guidance of your GP. Why endurance athletes are particularly at risk, you read in iron deficiency in athletes.

7. Omega-3

For omega-3 from fish oil the evidence is modest, with a possible anti-inflammatory and recovery-supporting effect. The effect on pure muscle growth is unclear. The base is oily fish twice a week, which the Voedingscentrum also advises, and a supplement is mainly relevant if you do not eat that fish.

Your status is read off your omega-3 index.

What that index says about your heart and recovery sits in the omega-3 index.

8. Magnesium

Magnesium is only worthwhile if your intake is low, and the evidence for cramp and sleep is weak. Tricky detail: magnesium in your blood is a poor measure, because most of it sits in your cells and bones, not in your serum. So a normal serum value does not rule out a deficiency in your tissue.

That is why this is one you mainly get from food.

Nuts, green vegetables and wholegrains supply it fine. What magnesium does and does not do for cramp, sleep and recovery sits in magnesium for athletes.

The overrated category

This last one belongs here because it is sold so persistently, not because it works. This is the category that annoys me most, because it takes the most money for the least evidence. If you get enough protein, it adds almost nothing.

9. BCAAs (and why testo boosters belong here too)

BCAAs are sold as muscle builders, but with enough protein they do nothing extra. A widely cited review concludes that the claim that isolated BCAAs drive muscle protein synthesis is unwarranted (PMID 28852372). If you hit your 1.6 to 2.2 grams of protein per kilo, you already take in those amino acids.

Testo boosters belong in the same category.

For herbal mixes such as tribulus there is no convincing evidence that they raise testosterone in men with normal values. Instead of buying a booster, you are better off having your testosterone measured, so you know whether there is anything to raise at all.

Overview: the 9 supplements at a glance

This table sums up the list: how strong the evidence is, the common dose, and the blood value that tells you whether it adds anything for you.

Which supplements do you actually need?

For most athletes it comes down to three: creatine, enough protein, and possibly caffeine around your training. Those work regardless of your blood values. The rest is situational: vitamin D, iron, omega-3 and magnesium are only worthwhile if you take in too little of them, and you only know that once you measure it.

Anything beyond that is optional, not essential.

How do you know what you are missing?

By having the situational values measured before you buy anything. A panel that measures your vitamin D, ferritin and hormones in one draw shows which supplements genuinely add something for you and which are wasted money. Guessing is more expensive over time than measuring.

A broad panel such as the 360 Health gives you those situational values in one go, so you choose your supplements based on your blood and not on an advert.

What do you do with this list?

Start with the top four, because they work regardless of what your blood says. Then have your vitamin D and ferritin measured before you buy anything from the situational row. And skip the bottom category until you have a concrete reason to suspect a deficiency.

That way you spend money on what works, and not on what is well advertised.

Every blood test result includes a professional assessment by a BIG-registered doctor. For treatment decisions, discuss your results with your GP.

References

• Kreider RB, et al. International Society of Sports Nutrition position stand: safety and efficacy of creatine supplementation in exercise, sport, and medicine. Journal of the International Society of Sports Nutrition, 2017. PMID 28615996.
• Morton RW, et al. A systematic review, meta-analysis and meta-regression of the effect of protein supplementation on resistance training-induced gains in muscle mass and strength in healthy adults. British Journal of Sports Medicine, 2018. PMID 28698222.
• Guest NS, et al. International society of sports nutrition position stand: caffeine and exercise performance. Journal of the International Society of Sports Nutrition, 2021. PMID 33388079.
• Saunders B, et al. Beta-alanine supplementation to improve exercise capacity and performance: a systematic review and meta-analysis. British Journal of Sports Medicine, 2017. PMID 27797728.
• Sim M, et al. Iron considerations for the athlete: a narrative review. European Journal of Applied Physiology, 2019. PMID 31055680.
• Wolfe RR. Branched-chain amino acids and muscle protein synthesis in humans: myth or reality? Journal of the International Society of Sports Nutrition, 2017. PMID 28852372.