Gut Check looks at health claims made by studies, newsmakers, or conventional wisdom. We ask: Should you believe this?
Curcumin, a component of the spice turmeric, can prevent or treat Alzheimer’s disease.
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An internet search for “curcumin” and “Alzheimer’s” leads not only to commercial websites whose claims are clearly suspect but also to papers in scientific and medical journals. That’s how marketers can say “studies show” that curcumin helps immune cells suck up amyloid plaques and that people with dementia who took turmeric capsules had miraculous improvements.
Those claims make their way into the popular press when even respected universities claim that “one of the most promising new treatments for Alzheimer’s disease may already be in your kitchen” and that “curcumin has demonstrated ability to … bind and destroy the beta-amyloid plaques present in Alzheimer’s.”
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Tracing the claims feels like a neurological game of telephone, with the original message unrecognizable by the time it’s cited by later studies. One 2008 paper, for instance, claimed that curcumin “decreased Beta-amyloid plaques, delayed degradation of neurons,” and improved “the overall memory in [Alzheimer’s] patients.” Let’s trace those assertions.
The “decreased plaques” claim comes from a study in which immune cells called macrophages, taken from the blood of six people with Alzheimer’s, were grown in lab dishes. After curcumin was added to the dishes, cells from three patients devoured the main component of plaques (the sticky deposits in the brains of Alzheimer’s patients) more than curcumin-less macrophages did.
The number of red flags here rival those at Turkish national holiday celebrations. For one, cells from the other three patients showed no such effect of curcumin, and there’s no evidence this happens in real life rather than lab dishes. To happen in real life and real bodies, ingested curcumin would have to get from the gut into the bloodstream and then the brain. But “an incredibly small fraction of what you ingest even gets to where it would need to go to affect Alzheimer’s,” said Penny Dacks of the Alzheimer’s Drug Discovery Foundation, whose new website evaluates claims that various foods, drugs, and supplements protect against or treat Alzheimer’s.
Most crucially, it’s far from established that macrophages (called microglia when they’re in the brain) play an important role in Alzheimer’s. Although they might clear amyloid, they “can also activate inflammatory cascades that may accelerate damage to [brain] tissue,” said Dacks.
The “delays degradation of neurons” claim fares no better. Its source is a study that is peripheral to the claim. The study reported that curcumin reduced the number of free radicals (again, in lab dishes), and leapt from there to assert that, because free radicals attack neurons (a process that has not been shown to play an important role in Alzheimer’s), then eliminating them with curcumin (which has also not been proved in people rather than lab dishes) must delay the degradation of neurons in patients’ brains. That’s a triple play of unproved assertion stacked on unproved assertion.
The main source of the “improves memory” claim are studies reporting that people who eat a lot of curry, which contains turmeric, have better cognitive function than people who eat little. But that says nothing about cause and effect; maybe smart people eat more curry than less-smart people do. As for an oft-cited 2012 study in a journal devoted to traditional Indian medicine, which claimed miraculous improvements in three patients with dementia who took turmeric capsules: One improved from 12 to 17 on a 30-point standard mental exam; the other two had no such improvement but, the researchers reported, began recognizing family members again. Needless to say, three patients of whom only one improved on an objective scale is an awfully thin reed to hang a claim of “improves memory” on.
One small study in healthy adults found an effect on working memory so minuscule it wouldn’t be noticed in real life, Dacks said. Another found that curcumin boosted cognition, but only because, inexplicably, the comparison group got worse, not because the curcumin group improved.
There is no rigorous evidence that curcumin does anything for Alzheimer’s.