Buying supplements: which dietary supplements actually work
The 30-second answer
Most supplement marketing claims are not scientifically supported. After reviewing the evidence, only a handful of supplements have solid, partly EU-authorised support for most healthy adults: creatine, protein, vitamin D, omega-3 and magnesium — and even these only work under specific conditions (e.g. only with an actual deficiency, only combined with resistance training). Hyped topics like NAD+/NMN or collagen have little robust human data behind them. Dietary supplements never replace a balanced, varied diet or medical advice — and the right dose for you is something to discuss with a doctor or pharmacist, not with an article.
What does it actually do for you?
| Area | Evidence | Statement |
|---|---|---|
| A supplement can replace a balanced diet | — | Honest no — this is a legal requirement in the EU: supplements are meant to supplement the general diet, not replace it. Get the diet right first, then supplement where there is an actual gap. |
| Only five supplements have solid, partly EU-authorised evidence for most healthy adults | A | Creatine, protein, vitamin D, omega-3 (EPA/DHA) and magnesium each carry at least one authorised EU health claim — each tied to specific conditions (amount, target group, training context). Details for each below. |
| A well-known brand or a higher price automatically means a better or purer product | — | Honest no: price and brand recognition say nothing about purity or contamination. What matters is independent testing (e.g. for heavy metals and contaminants) and accurate, complete labelling — not the price tag. |
| Longevity and beauty hypes (e.g. NAD+/NMN, collagen) are adequately proven in humans | — | Honest no: for NAD+ precursors (NMN/NR), robust human data on aging, strength or lifespan is essentially absent, and NMN is not authorised as a food in the EU. Collagen does not carry a single authorised EU claim of its own. See the linked fact checks below. |
| More is automatically better — a higher dose works stronger | — | Honest no: each of the five recommended supplements has its own safety upper limit, named in its own article (e.g. magnesium 250 mg/day as a supplement per German BfR guidance, vitamin D 4,000 IU/day). Above that, only the risk goes up, not the benefit. |
Evidence grades: A = strongly supported · B = supported in the right context · C = emerging/mixed evidence · D = experimental · — = no proven benefit. Quoted statements with a regulation number are officially reviewed health claims authorised by the EU — we use only those.
Creatine: what it does, what it does not, what to look for when buying
What it does: Two authorised EU claims (Reg. (EU) 432/2012 and Reg. (EU) 2017/672): from 3 g daily, creatine increases physical performance in successive bursts of short-term, high-intensity exercise, and in adults over 55 combined with resistance training at least three times a week, it can enhance the effect of that training on muscle strength.
What it does not: For classic endurance performance (running, cycling), studies show little direct benefit; without resistance training it just tops up your stores, with no noticeable effect.
What to look for when buying: creatine monohydrate is the studied standard form — pricier forms like "HCL" or "Kre-Alkalyn" have no proven added benefit. Studied range for guidance: 3–5 g daily, ongoing; a loading phase is unnecessary. Individual dosing and suitability: discuss with a doctor or pharmacist.
Protein powder: what it does, what it does not, what to look for when buying
What it does: Three authorised EU claims (Reg. (EU) 432/2012): protein contributes to a growth and to the maintenance of muscle mass, and to the maintenance of normal bones — growth requires resistance training.
What it does not: A shake before training does not make you acutely stronger (protein works over weeks, not hours), and the "damages your kidneys" myth is considered debunked for healthy people — with existing kidney disease, a doctor decides the amount.
What to look for when buying: studied range for people who train: roughly 1.2–1.6 g total protein per kg body weight per day, spread across 3–4 servings — a meta-analysis found little additional benefit above about 1.6 g/kg. Whey is cheap and fast-absorbing, plant blends (e.g. pea + rice) combine into a complete profile — the practical difference between forms is small. Look for contaminant-tested products; pricey "anabolic formula" add-ons are usually skippable.
Vitamin D: what it does, what it does not, what to look for when buying
What it does: Several authorised EU claims (Reg. (EU) 432/2012, plus Reg. (EU) 1228/2014 for the falls claim): maintenance of normal bones, normal muscle function, normal immune function — and, at 20 µg (800 IU) daily, a dedicated claim on reducing the risk of falling linked to postural instability and muscle weakness in people over 60.
What it does not: not an energy booster, not a weight-loss aid, not insurance against infections. People who are already well supplied have little to nothing to gain from extra vitamin D according to current evidence.
What to look for when buying: get your 25-OH vitamin D level checked by a doctor first, then decide. Typical maintenance doses run 800–2,000 IU (20–50 µg) daily, taken with a meal (fat-soluble); the long-term upper limit without medical supervision is 4,000 IU (100 µg) daily.
Omega-3 (EPA/DHA): what it does, what it does not, what to look for when buying
What it does: Authorised EU claims (Reg. (EU) 432/2012): from 250 mg daily, EPA and DHA contribute to normal heart function, and DHA additionally to the maintenance of normal brain function and normal vision.
What it does not: not a weight-loss aid, not a muscle-building booster. Whether capsules provide additional cardiovascular protection for people who are already healthy and well-nourished is contested based on the large trials of recent years.
What to look for when buying: guideline range 250–500 mg EPA+DHA daily, taken with a meal; vegans and vegetarians can use algae oil (same active compounds, same claims). Check for freshness and verified purity — rancid oil is noticeable by smell when you bite into a capsule.
Magnesium: what it does, what it does not, what to look for when buying
What it does: an unusually long list of authorised EU claims (Reg. (EU) 432/2012): reduction of tiredness and fatigue, normal muscle and nervous-system function, normal psychological function, maintenance of normal bones — each conditional on a prior shortfall in supply.
What it does not: for ordinary nighttime leg cramps, the pooled evidence (Cochrane) shows no clear benefit — precisely the reason most people buy it.
What to look for when buying: Germany's BfR recommends a maximum of 250 mg magnesium per day from supplements, ideally split across two servings. Citrate and glycinate are considered well tolerated, oxide is cheaper and somewhat less well absorbed — in practice the differences are smaller than the marketing suggests.
Lots of hype, little proof: a critical look
Not every popular supplement is well supported. Two examples we deliberately assess critically instead of recommending — which is also why you will not find a purchase link for them below:
- NAD+, NMN & NR — the most expensive promise in the longevity space: that these precursors raise NAD blood levels is well established. A benefit for people (muscle strength, metabolism, lifespan) is not — recent meta-analyses and systematic reviews found no effect on muscle mass, grip strength or blood sugar. NMN is also not authorised as a novel food in the EU. Full fact check: NAD+, NMN & NR.
- Collagen — carries no authorised EU claim of its own (the vitamin C claim on many tubs belongs to the added vitamin C, not the collagen). The evidence on skin and joints shows small effects in mostly manufacturer-funded studies. Collagen you drink is broken down like any protein into building blocks — "drink it and it gets built straight back in" is not how biology works. Full fact check: collagen.
Our standard: we do not recommend a supplement just because the story behind it sounds plausible or is well marketed.
What to check for with any supplement before you buy
- Choose the form the evidence studied, not the one marketed hardest: the studied standard form (e.g. creatine monohydrate, magnesium citrate) is almost always the sensible choice — pricier specialty forms rarely have proven added benefit.
- Base the dose on the studied range, not the manufacturer's promise. Guideline doses for each supplement are above and in the linked articles.
- Independent purity testing: look for contaminant or heavy-metal testing information, especially for fish oil and plant extracts.
- Read the mandatory label information: recommended daily serving, a warning not to exceed it, and a statement that the product is not a substitute for a balanced diet.
- Add up your total intake across all products: a multivitamin plus a standalone product (e.g. magnesium or vitamin D) stacks up — double supplementation is a common cause of unnecessarily high intake.
- Medication, pregnancy, existing conditions: check with a doctor or pharmacist before supplementing, especially around kidney, thyroid or clotting issues.
Honest notes before you buy
- Editorial choices are independent of commission: this selection follows the evidence in our fact checks only, not the size of any potential commission.
- Dietary supplements are not a substitute for a balanced, varied diet and a healthy lifestyle — and should be kept out of the reach of children.
- Prices and availability change constantly. Check them directly with the retailer before buying — the price shown in the shop at the time of purchase is always binding, not this article.
Safety & dosing
- Dosing
- Guideline doses differ by supplement and are listed in each linked article (e.g. creatine 3–5 g/day, vitamin D 800–2,000 IU based on a measured blood level, magnesium up to 250 mg/day as a supplement). The right dose for you is something to discuss with a doctor or pharmacist.
- Upper limit
- Each supplement has its own safety upper limit, named in its own article (e.g. magnesium 250 mg/day per German BfR guidance or 350 mg/day US UL as a supplement, vitamin D 4,000 IU/day, omega-3 up to 5 g EPA+DHA/day per EFSA). If you take several products at once, add up the total intake across all of them.
- Interactions
- Medication use, pregnancy/breastfeeding, or existing conditions (especially kidney, thyroid, clotting): check with a doctor or pharmacist before supplementing.
- Keep dietary supplements out of the reach of young children.
- Get persistent symptoms (e.g. fatigue, muscle cramps) checked by a doctor first, rather than masking them with supplements.
Discuss dosing and suitability for you with a doctor or pharmacist.
Sources
- 1. EU Register of authorised health claims (Reg. (EU) 432/2012 and related) — basis for every claim named in this article — Accessed on: 2026-09-25
- 2. German Dietary Supplements Ordinance (NemV) — legal framework, mandatory labelling and the "supplement, not replace" principle — Accessed on: 2026-09-25
- 3. Verbraucherzentrale (German consumer advice centre) — dietary supplements: overview, critical assessment and buying tips — Accessed on: 2026-09-25
- 4. NIH Office of Dietary Supplements — Dietary Supplements: What You Need to Know — Accessed on: 2026-09-25
Dietary supplements are not a substitute for a balanced, varied diet and a healthy lifestyle. This article is for information purposes only and does not replace medical advice.