Sources and evidence

The sources we prefer

Where they exist, we start with sources that weigh up many studies or set official guidance:

Government and public-health bodies, such as national health services and health agencies, and international bodies such as the World Health Organization.
Recognised health and research institutions, including official reference sources for nutrients and supplements.
Professional guidelines from recognised clinical and professional organisations.
Systematic reviews and meta-analyses, which collect and assess all the studies on a question, not a selection of them.
Individual peer-reviewed studies, used to explain a specific finding, to cover a question no review has addressed yet, or to show where research is heading.

We treat press releases, marketing material, product claims and social-media posts as claims to check, not as evidence. We may quote them so we can explain what the research actually shows.

Why not all evidence is equal

A single small study is a weaker basis for advice than consistent results across many larger ones. When we weigh a finding, we look at:

Who was studied: people or animals, and whether they resemble our readers.
How the study was designed: a randomised controlled trial can test cause and effect, while an observational study can only show that two things tend to go together.
Size and length: how many people took part and for how long.
Consistency: whether other studies found the same thing.
What was measured: a real-world outcome, or a marker in the blood that may or may not translate into one.

How we describe the strength of evidence

We use consistent wording so the language itself tells you how confident to be:

Evidence	What that means	How we phrase it
Strong	Consistent results from good studies in people	“does”, “reduces”, “improves”
Moderate	Good evidence, but some doubt remains	“likely”, “probably”
Limited	Small, short or few studies	“may”, “might”, “small studies suggest”
Very limited	Little or no research in people	“it’s unclear”, “not known”, “hasn’t been tested”

We do not use “proven”, “clinically proven” or “guaranteed”.

How we handle particular kinds of evidence

Observational findings. When research shows that people who do X tend to have outcome Y, we say they are “linked” or “associated”. We don’t say X causes Y unless trials support that.
Early or preliminary research. Animal, laboratory and pilot studies can show where science is heading, but we don’t turn them into advice for people.
Mixed or conflicting evidence. We say the studies disagree. Where we can, we explain why, for example because they studied different people, doses or durations. We describe the sensible middle ground, not the most exciting result.
Uncertainty. “We don’t know yet” is a legitimate answer. We would rather say it plainly than fill the gap with confident-sounding advice.
Low-risk habits. When something is cheap, safe and pleasant, weaker evidence may still make it worth trying. We say when we’re making that kind of judgement, and we keep it separate from what the research found.

Benefits, harms and who should check first

Every time we describe a possible benefit, we also aim to describe what isn’t known, any risks or side effects, and the people who should speak to a professional first. That includes people who are pregnant, those taking medication, and those with relevant health conditions. This matters most for supplements, which can interact with medicines.

Numbers and doses

We don’t invent statistics. Where an article gives an amount or dose, it should come from an official reference source, and we point out that individual needs differ.

Citing sources

Our aim is for articles to list their key sources at the end, so you can check them yourself. Not every page on PLENTIST does this yet.

Spotted a problem?

If you think we’ve misread or misrepresented the evidence, please tell us. Our corrections and updates policy explains how we deal with it. You can also read our wider editorial policy.