Coffee is good for you. Then it is bad. Then good again. Eggs raise your cholesterol, until they do not. If you have ever felt whiplash from health headlines, you are not alone. The problem usually is not the research itself. It is how a single study gets squeezed into a catchy headline. Once you know a few questions to ask, you can judge most health news, and most supplement claims, in a couple of minutes.
Question 1: Was the study done in people?
A surprising number of headlines are based on studies in mice, rats or cells in a lab dish. These studies are important for science, but many results never carry over to humans. If the article does not mention people, look for words like "in mice" or "in cells" further down. A compound that kills cancer cells in a dish is not the same as a cancer treatment.
Question 2: What kind of study was it?
There are two broad types:
- Observational studies watch large groups of people and look for patterns. For example, people who drink coffee have lower rates of a certain disease. These studies are useful but cannot prove cause and effect. Coffee drinkers might also be different in other ways, such as income, smoking habits or overall health.
- Randomized controlled trials assign people by chance to take a treatment or a placebo and then compare the results. This is the strongest way to test whether something actually works.
When a headline says something "lowers your risk," check whether it was a trial or an observational study. Words like "linked to" or "associated with" are a clue that it was observational.
Question 3: How many people, and for how long?
A study of 20 people for two weeks tells you much less than a study of 20,000 people for five years. Small studies are more likely to produce results that do not hold up later. Short studies cannot tell you about long-term effects.
Question 4: How big was the effect?
A result can be "statistically significant" and still be tiny in real life. Pay attention to the actual numbers. Also watch out for relative risk, which can make small changes sound huge. "Cuts your risk in half" might mean going from 2 in 1,000 people to 1 in 1,000. We explain this in detail in relative risk vs absolute risk.
Question 5: Who were the people studied?
A supplement that helped older adults with a deficiency may do nothing for healthy 30-year-olds. A trial in elite athletes may not apply to weekend walkers. Ask yourself whether the people in the study are similar to you.
Question 6: Who paid for it?
Industry funding does not automatically make a study wrong, but it is worth knowing. Studies paid for by the company selling the product are more likely to report positive results. Look for whether the results have been repeated by independent researchers.
Question 7: Is this one study, or the weight of the evidence?
Science moves slowly. A single surprising study is a reason to pay attention, not a reason to change your habits. More reliable are reviews that combine the results of many studies, and recommendations from neutral bodies such as the NIH Office of Dietary Supplements or MedlinePlus.
Question 8: Was it published, and where?
Some headlines come from conference talks or preprints, which have not yet been checked by other scientists. That does not make them wrong, but the findings are more preliminary.
Using this checklist on supplement claims
Supplement marketing often cites "clinical studies." Run the same questions:
- Was it the same ingredient, in the same form and dose, as the product?
- Was it a real trial in people, or a lab study?
- How many people and how long?
- Who funded it?
You will often find that the study used a different form or a much higher dose than the product contains. Our article on manufacturer claims vs evidence has real examples.
The bottom line
Most bad health decisions come from overreacting to one study. Slow down, ask whether it was done in people, how big and how long it was, how large the effect was, and whether other studies agree. With a little practice, you will start spotting weak headlines instantly and save yourself money on supplements that were never really proven.