How to evaluate supplements: an evidence-led guide

Two tubs sit side by side on a shelf. One lists a single ingredient and an amount. The other lists nine ingredients and a promise. Which one is better? Neither, yet: you haven't said what you want it to do.

That is the whole idea of this guide. Start with the need, then look at the evidence, the product, the rules where you live and the safety questions. It's a short checklist you can reuse for any supplement, and buying nothing is a perfectly good outcome.

Start with a specific need

"Better health" is too broad to evaluate. A nutritional requirement, an identified deficiency and a wish to feel more focused are three different questions. Write your goal down before you research products, and ask whether food, an existing treatment or a professional assessment is the sensible first step.

Supplements can have a role, but they cannot replace a varied diet, and how useful one is depends on the ingredient and the person taking it. NIH Office of Dietary Supplements, What You Need to Know. The Dutch Voedingscentrum puts the starting point plainly: many people do not need supplements, although some groups are advised to take specific ones. Voedingscentrum, Supplementen and Heb ik extra vitamines en mineralen nodig?.

Match the evidence to the claim

A headline saying an ingredient "works" leaves out the interesting part. Who was studied? What preparation did they get? What was it compared with, and what actually changed? Evidence about a diagnosed condition doesn't automatically carry over to healthy adults.

• Research detail: Participants; Question to ask: Were they similar to the intended user?
• Research detail: Preparation; Question to ask: Was it the same ingredient, form and combination?
• Research detail: Outcome; Question to ask: Did people feel or function better, or did a laboratory marker change?
• Research detail: Comparison; Question to ask: Was there a suitable control group?

Animal and laboratory findings give researchers a reason to investigate. They are not proof of a benefit in people. NCCIH, Checklist for Understanding Health News Stories.

Read beyond the abstract

A study's limitations matter as much as its conclusion. Look at sample size, study duration, missing participants, funding and whether other researchers found something similar. A result can be statistically detectable and still too small to notice in everyday life.

Repeated findings build confidence; one positive study leaves more room for doubt. NCCIH, How To Make Sense of a Scientific Journal Article.

Separate product quality from effectiveness

An accurately labelled product and an effective one are different things. Testing can answer specific quality questions; it cannot turn a weak health claim into a strong one.

• Product information: Ingredient amounts and serving size; What it helps you assess: What the stated daily portion contains
• Product information: Batch-specific laboratory report; What it helps you assess: Which substances and contaminants were tested
• Product information: Storage instructions and expiry; What it helps you assess: How the product is intended to be stored
• Product information: Research on the actual preparation; What it helps you assess: Whether the advertised use was studied

Ask what a certificate covers rather than treating a logo as a promise. Independent quality seals do not guarantee safety or effectiveness. NIH ODS, What You Need to Know, quality section. Our guide to reading supplement labels shows how to turn a label into a daily portion and a price per portion.

Check the European context

The NIH and NCCIH pages above are American. Their advice on weighing evidence travels well; the rules around the product do not, so here is what the EU and Netherlands sources say (all read on 14 October 2026).

• Supplements are food. EFSA states that in the EU food supplements are regulated as foods, with Directive 2002/46/EC as the main law, and that the business placing a product on the market is responsible for its safety. EFSA, Food supplements. In the Netherlands the NVWA says the same: companies are responsible for the products they sell, and the authority steps in when a product breaks the rules. NVWA, Voedingssupplementen.
• The label has required content. The Directive says a supplement's labelling must not attribute to it the property of preventing, treating or curing a human disease, and must give the recommended daily portion, a warning not to exceed it, a statement that supplements are not a substitute for a varied diet, and a warning to keep it out of reach of young children. Directive 2002/46/EC, Article 6.
• Claims have a register. The EU register of health claims lists authorised claims with their conditions of use, and non-authorised claims with the reasons. It also notes that some claims, including ones about botanical substances, are missing because the assessment or review is not finished. An authorised statement about a nutrient is not blanket approval of every promise made about a finished product. European Commission, EU register of health claims.
• Amounts are not harmonised yet. The Commission's supplements page says maximum and minimum amounts are envisaged in the Directive but no proposal has yet been presented, and EFSA likewise reports no binding EU-wide maximum or minimum levels for supplement ingredients. European Commission, Food supplements.
• Herbs deserve extra care. The NVWA says the health effects of herbal supplements are usually not well studied, and that combining some with medicines can be harmful. Voedingscentrum likewise says the effects of herbal preparations are often not well researched and that they can sometimes be harmful. The NVWA also points out that some supplements on its blocklist may not be sold but turn up anyway. Substances with no history of safe use in the EU before 1997 fall under novel-food rules, which EFSA assesses.

Rules differ from country to country and change over time. For a specific smartshop product, see buying in the Netherlands and EU: check the product and the country.

Safety: medicines, surgery and life stage

"Natural" tells you where something came from. It is not a safety check. NCCIH recommends discussing supplement use with health care providers, and the NVWA says to report side effects to Lareb, the Dutch adverse-reaction centre, and to talk to your doctor. Our practical suggestion is to bring a pharmacist or clinician the exact products if you take medicines, are pregnant or breastfeeding, are choosing a product for a child, or have surgery planned. Bring the full ingredient list, including products you use only occasionally. NCCIH, Using Dietary Supplements Wisely. For the specifics, read our guide to supplement and medicine interactions.

Useful questions to take with you: is there a reason to take this, what uncertainty remains, could it interact with my medicines, and when should the decision be reviewed?

Keep a simple decision record

Record the proposed purpose, the evidence you relied on, unanswered questions and any professional advice. If use is appropriate, agree how its value and tolerability will be reviewed. Don't read every change in how you feel as proof of an ingredient's effect.

What a good buy looks like

We would pay for a product that fits a clear need, has an understandable label and offers relevant evidence, not for an impressive ingredient count. A simple, cheaper option can be the sensible choice. Compare the daily portion and ingredient amounts, and check medicine interactions before adding it to your routine. This is editorial judgement, not an individual treatment recommendation.

Frequently asked questions

Do I need a foundation stack?

No. Start with your diet, circumstances and a specific need. An influencer's shopping basket is not your assessment.

Is a study enough to recommend a product?

It is a starting point. Check the preparation, population and outcome, then consider the wider evidence and safety information.

Does a higher price mean better evidence?

Price does not tell you whether the intended use has been studied. Assess the evidence and product information separately.

What should I ask a pharmacist?

Bring exact product names, ingredients and amounts, alongside your medicines. Ask whether the proposed use is appropriate and which interactions or warning signs matter for you.

Written by Smart Supplements with AI assistance from the sources linked in the text. It has not been reviewed by a clinician.

Last updated: 14 October 2026

This article is for informational purposes only and is not intended as medical advice. Always consult a healthcare professional before starting any new supplement, especially if you take prescription medication.