Does vitamin C stop you catching colds?
Decades of Cochrane trials find no meaningful drop in cold risk for ordinary adults, only a modest shortening of colds once they start.
By The Evidence Desk · 2 min read
What the science actually supports, and how firmly.
Dr Schwartz weighs the research behind common health claims. Two marks on everything we publish: how strong the evidence is, and which way it points.
The Verdicts desk
All verdictsClaim checkRefuted
Taking vitamin C regularly prevents the common cold in the general population.
For the average adult, regularly taking vitamin C does not meaningfully lower the chance of catching a cold. It may shorten colds slightly once they occur, and a clearer benefit appears only in people under brief, extreme physical exertion.
Moderate certainty—No effect
Claim checkRefuted
Eating sugar causes hyperactive behaviour in children.
Multiple double-blind trials, pooled in review, have not found that sugar causes hyperactivity in children. What changes is often the parent's expectation, not the child's behaviour.
High certainty—No effect
Claim checkUnproven
Every adult should drink eight glasses of water a day.
No strong evidence pins healthy adults to a fixed eight-glasses target. Needs vary widely, much of your intake comes from food and other drinks, and thirst is a reasonable guide for most people.
Moderate certainty—No effect
Reviews & analysis
Methods
How we weigh the evidence
Every claim we assess carries the same two marks: how strong the evidence is, and which way it points. This is the method behind them, and the reason we sometimes say "we don't know."
High certainty
Methods
The evidence pyramid: why not all studies are equal
"A study found" tells you almost nothing until you know what kind of study it was. A quick tour from anecdote to meta-analysis.
High certainty
Methods
Relative vs absolute risk: the trick behind scary headlines
"Doubles your risk" and "raises it from 1 in 10,000 to 2 in 10,000" can describe the exact same finding. One sells papers; the other tells you what to do.
High certainty
Consensus
What scientists mean by "consensus"
A scientific consensus is not a vote, and not a demand for silence. It is what remains standing after decades of people trying to knock it down.
High certainty
Verdicts
How a single study becomes a myth
The pipeline from a modest finding to a confident health myth is short, well-worn, and easy to spot once you know the stations it passes through.
Moderate certainty
Evidence
Where the evidence stands: physical activity
On a subject where much is contested, this one is not: across an enormous body of research, regular movement is among the best-supported things you can do for your health.
High certainty↑Benefit