There's a weird story around today that says eating Marmite "may help prevent you getting dementia".
It's based on this study, published in the Journal of Psychopharmacology and carried out by psychologists at the University of York.
The study compared the brain activity of people who'd eaten a teaspoonful of Marmite every day with that of people who'd had a teaspoonful of smooth peanut butter.
It found that the levels of a chemical called gamma-aminobutyric acid (GABA) were higher in the subjects who'd had Marmite (or, in scientific journal language, "a yeast extract product") than those who'd had peanut butter. GABA is an inhibitory neurotransmitter, meaning it reduces the response of neurons in the brain. The study also found that in subjects who had had the Marmite, the brain's response to visual stimuli was reduced.
The trouble is, the study at no point mentions dementia, or Alzheimer's, at all.
If you've got access to the full paper, go and open it and press Ctrl-F to search the text. There's not a single mention of Alzheimer's or dementia.
It does say: "Atypical levels of GABA have been associated with disorders such as epilepsy, autism, anxiety and depression, suggesting potential therapeutic benefits to modulating its concentration," and that the findings suggest "possible clinical benefits" in patients with abnormal levels of GABA. But that obviously doesn't say anything about dementia.
And in fact it COULDN'T reasonably be expected to say anything about dementia, because it looked only at 28 people in their early twenties.
"This is a pretty good study," Dr Pete Etchells, a psychologist at Bath Spa University, told BuzzFeed News. "They got people to eat five millilitres of Marmite every day for a month, so at least there was an attempt to look at long term effects. The take-home is that Marmite affects brain function, and the effects are likely through the high levels of B12 in it."
But, he said, "It's a small study of vision, it doesn't test memory functioning, and uses healthy adults with a mean age of 22. So it can't say anything about Alzheimer's."
Media claims that eating Marmite every day could "prevent Alzheimer's" are "horseshit", he said.
No one really seems to know where the dementia link comes from. The senior researcher on the study told BuzzFeed News he was "bemused" by the response.
Dr Daniel Baker said: "I'm slightly bemused as to where it's come from. We've said nothing about Alzheimer's or dementia in our press release or article. We haven't tested for it, we aren't making any claims.
"We were incredibly deliberate and careful in not mentioning any specific diseases or disorders in the press release, precisely because we didn't want this to happen. It's funny, because GABA has been linked to a massive number of disorders, and apparently dementia and Alzheimer's are among them, but it's not the obvious one.
"We thought people would mention epilepsy and anxiety, and perhaps schizophrenia, but for some reason they've gone with this."
The Times, The Independent, the Daily Mirror, Wired, and the Huffington Post, for the record, did report the study with more defensible references to epilepsy. But even that is somewhat speculative, since it's a pilot study looking at 28 healthy people.
He wondered whether the dementia link was sparked by a press release from the Alzheimer's Society.
The release quoted the charity's head of research, Dr James Pickett, as saying: "There’s no way to say from this study whether eating Marmite does affect your dementia risk." That comment was embedded in a longer quote about how "our diet plays an important role in the way our brain functions", so all the media outlets just quoted it in the apparent assumption that no one would notice it directly contradicted their headlines.
But it looks like that wasn't what started the whole thing – BuzzFeed News understands that several journalists contacted the society specifically asking for a quote on the Marmite-dementia link, and that was what sparked them to put the release out.
In a rather stronger statement, Pickett told BuzzFeed News: “This study only looked at people in their twenties over a short period of time, so it can’t tell us anything about dementia risk.”
Anyway, the long and the short of it is: This study doesn't show that Marmite can prevent Alzheimer's, the study couldn't possibly show that, and no one involved in the study claims it does.
Tom Chivers is a science writer for BuzzFeed and is based in London.
Contact Tom Chivers at email@example.com.
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