Studies explained

How to read supplement studies: a practical guide to the evidence

Coenzyme Q10, zinc or quercetin: ‘the evidence’ comes up everywhere. We show you what to look out for when you read studies on food supplements.

7 min read7 sources
A woman in reading glasses looks through supplement studies with simple charts
In this article
  1. Key points
  2. What does ‘the evidence’ mean?
  3. What types of study are there?
  4. Why placebo, randomisation and blinding matter
  5. Peak level and area under the curve: what do absorption studies measure?
  6. Who paid for the study?
  7. A short checklist for the next study you read
  8. Frequently asked questions about reading studies
  9. Sources

Key points at a glance

  • ‘The evidence’ on a question describes how many studies there are, how good they are and whether they point the same way.
  • Observational studies and controlled trials on the same question can reach different results1.
  • Absorption studies measure the peak level and the area under the curve, in other words how much of a substance reaches the blood. They don’t record how the participants feel.
  • Studies of medicines and medical devices funded by manufacturers more often reach favourable results. For food supplements, too, that’s a reason to look more closely, but not a reason to dismiss a study2.

What does ‘the evidence’ mean?

If you search for ‘coenzyme Q10 studies’ or ‘zinc studies’, you usually want to know one thing: is it proven? The honest answer is rarely a clear yes or no. The evidence describes how many studies there are, how well they’ve been carried out and whether their results fit together.

So a single study is only one building block. Only when several careful studies find similar results can you call the evidence solid. The sections below show you how to recognise quality.

What types of study are there?

  • Laboratory studies on cells or animals show whether a mechanism is possible. Their results can’t simply be applied to humans.
  • Observational studies record associations, for example between diet and sleep. They don’t show which is the cause and which is the effect.
  • In randomised controlled trials, chance decides who gets the substance and who gets a placebo. This is the best way to test cause and effect.
  • A review brings together several studies on one question.

Magnesium and sleep show how much this difference matters. A review found an association between magnesium and sleep quality in observational studies, but contradictory results in randomised controlled trials1. You can read more in our article magnesium and sleep: what the studies have looked at.

Reviews traditionally sit at the very top of the well-known evidence pyramid. Some experts suggest seeing them instead as a tool for weighing up and summarising existing studies3. A review built on weak studies is still a weak basis.

Why placebo, randomisation and blinding matter

A placebo looks like the real product but doesn’t contain the substance. This separates what the substance does from what expectation does, which matters especially when results come from questionnaires.

A Cochrane review of more than 200 studies that compared a placebo group with a group given nothing at all concluded that, in certain situations, placebos can influence what participants report about themselves4. Small studies were among those that showed larger placebo effects4. Studies that rely only on self-reported questionnaires are therefore worth reading with some caution.

In a double-blind study, neither the participants nor the researchers know who is receiving what. In a crossover study, every participant receives all the variants, one after another. The international CONSORT guideline sets out what a report on a randomised controlled trial should contain, and its 2025 version has a checklist of 30 items5.

Peak level and area under the curve: what do absorption studies measure?

Many studies on liposomal forms are absorption studies. Participants take a dose, and blood samples are then taken several times. In a vitamin C study with 27 adults, this happened eleven times over a 24-hour period6.

This gives two key figures. The peak level is the highest value measured, and the area under the curve describes the amount over the whole period. In the study mentioned, the peak plasma level with the liposomal form was 27% higher than with conventional vitamin C, and the area under the curve was 21% higher6.

It’s just as important to know what such studies don’t show. A review on liposomal vitamin C found ten comparison studies, but only two that looked at possible effects on the body beyond blood levels7. A higher blood level is a measurement. What it means for how you feel has to be established by other studies.

Who paid for the study?

Many of the studies we describe in our articles were also funded by manufacturers. A Cochrane review of 75 papers on studies of medicines and medical devices found that manufacturer-funded studies more often had favourable results and conclusions than others2. On blinding, however, they scored well more often2.

Funding is usually stated at the end of a study, under headings such as ‘Funding’ or ‘Conflict of Interest’. It’s a reason to look more closely, but not proof that a result is wrong.

A short checklist for the next study you read

  1. Who was studied: healthy adults, older people, women only?
  2. How many participants were there, and how long did the study run?
  3. What was it compared with: a placebo, another form, or nothing at all?
  4. What was measured: a blood level, a questionnaire, or something that happened in everyday life?
  5. Who paid for the study?
  6. Does the result fit with other studies and reviews?
Worth knowing: A study result applies first and foremost to the formulation, amount and group that were studied. For other products with the same substance it’s an indication, but not evidence in its own right. In the EU, a health claim may only be used once it has been authorised after assessment by EFSA. One example of an authorised health claim is ‘Zinc contributes to the normal function of the immune system’.

Whether it’s vitamin C, zinc or coenzyme Q10, this checklist lets you assess the evidence on any substance yourself.

Frequently asked questions about reading studies

How do I find the evidence on coenzyme Q10 or quercetin?

The PubMed database is a good place to start. Look for reviews first, then check individual studies against the checklist. Our articles on coenzyme Q10 and quercetin explain what these substances are.

What is the evidence on shilajit or berberine?

There’s no authorised health claim in the UK or the EU for either substance. You can assess the studies that do exist yourself, using the checklist above. Our article shilajit: what’s behind the mountain resin? explains what the resin is.

What does ‘the evidence is limited’ mean?

Usually there are only a few studies, with small groups and a short duration, often not repeated by other researchers. That doesn’t mean a substance has no effect, only that the question hasn’t yet been studied well enough.

Sources

  1. Arab A, Rafie N, Amani R, Shirani F (2023). The Role of Magnesium in Sleep Health: a Systematic Review of Available Literature. Biological Trace Element Research 201(1):121-128. DOI
  2. Lundh A, Lexchin J, Mintzes B, Schroll JB, Bero L (2017). Industry sponsorship and research outcome. Cochrane Database of Systematic Reviews 2017(2):MR000033. DOI
  3. Murad MH, Asi N, Alsawas M, Alahdab F (2016). New evidence pyramid. Evidence Based Medicine 21(4):125-127. DOI
  4. Hróbjartsson A, Gøtzsche PC (2010). Placebo interventions for all clinical conditions. Cochrane Database of Systematic Reviews 2010(1):CD003974. DOI
  5. Hopewell S, Chan AW, Collins GS, et al. (2025). CONSORT 2025 statement: updated guideline for reporting randomised trials. BMJ 389:e081123. DOI
  6. Purpura M, Jäger R, Godavarthi A, Bhaskarachar D, Tinsley GM (2024). Liposomal delivery enhances absorption of vitamin C into plasma and leukocytes: a double-blind, placebo-controlled, randomized trial. European Journal of Nutrition 63(8):3037-3046. DOI
  7. Carr AC (2025). Do Liposomal Vitamin C Formulations Have Improved Bioavailability? A Scoping Review Identifying Future Research Directions. Basic & Clinical Pharmacology & Toxicology 137(1):e70067. DOI

This article is for general information only and should not replace medical advice. Food supplements are not a substitute for a balanced and varied diet and a healthy lifestyle.

Written by
Melinava Editorial Team
Our editorial team writes about liposomes, nutrients and scientific studies.
More about us

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