The Daily Mail reported today that “eating a curry once (or twice) a week could stave off dementia.”
Sadly, this mouth-watering headline is not a good representation of the research. The study in question tested the effects of curcumin (a chemical found in the spice turmeric) on fruit flies. It found that curcumin improved lifespan and activity in some genetically engineered fruit fly models of Alzheimer’s disease. However, some other fruit flies, including the normal fruit flies, those eating actually died more quickly.
This type of study is essential for the initial testing of chemicals that may be of some benefit to humans. Chemicals showing beneficial effects and sufficient safety in animal studies need to be tested in humans before we can know what their true effects on a disease are. However, the promising effects of many chemicals seen in animals are not replicated in humans.
Despite what the papers have reported, this study cannot tell us whether a weekly curry will stave off Alzheimer’s disease or other forms of dementia.
Where did the story come from?
The study was carried out by researchers from Linköping University in Sweden.
It was funded by The Knut and Alice Wallenberg Foundation, Alice and Georg Olsson, The Swedish Foundation for Strategic Research, ‘Hjärnfonden’ (the Brain Foundation), The Swedish Research Council, the Gustaf V Foundation, and the European Union FP-7 Health project LUPAS.
The study was published in the peer-reviewed scientific journal Public Library of Science One.
The Daily Mail reported that the study was in fruit flies (Drosophila melanogaster) and used the chemical curcumin. However, the newspaper's headline suggesting that eating a curry once or twice a week may stave off dementia is not representative of this research.
What kind of research was this?
This was an animal study looking at the effect of the chemical curcumin on fruit fly models of Alzheimer’s disease. Curcumin is found in turmeric, a spice commonly used in curry recipes such as korma and jalfrezi. Previous studies have suggested that curacumin may help reduce the build-up of toxic amyloid beta that occurs in the brain of people with Alzheimer’s disease.
Animal models of human diseases are used in the initial testing of chemicals that may be beneficial to humans. It is easier and safer to do these early tests in animals in the laboratory than in humans. These models replicate specific aspects of the disease in question, but due to differences between species, do not fully represent the human condition.
As fruit flies are not mammals like humans, any chemicals found to show promise would then also need to be tested in a mammal species such as mice. Although certain chemicals may be effective and safe when tested on mammals, they then need to be tested in humans to see if they are really beneficial to us as well as safe to use.
What did the research involve?
The researchers used fruit flies that had been genetically engineered to replicate (to a certain extent) what happens in the brains of people with Alzheimer’s disease. They used five different types of fruit flies engineered to produce different sections of the protein amyloid beta or another protein called tau. Both of these proteins build up and form abnormal insoluble deposits called plaques and tangles in the brains of people with Alzheimer’s disease. These fruit flies are less active than normal ones of the same age, and have a shortened lifespan.
The researchers carried out various experiments where they fed the genetically engineered and normal fruit flies different amounts of curcumin. They looked at the effect of the curcumin on the fruit flies’ activity and lifespan compared to the same types of flies not fed curcumin. They also looked at how curcumin affected the build-up of amyloid beta in the brains of the flies.
What were the basic results?
The researchers found that the effect of curcumin on lifespan depended on the concentration of curcumin used and the type of fly being tested:
- increasing concentrations of curcumin reduced lifespan in normal (control) fruit flies
- two of the five Alzheimer’s model fly strains also died sooner with high curcumin dose
- three of the Alzheimer’s model fly strains lived longer with the low and intermediate doses of curcumin, although this was still shorter than the lifespan of the normal untreated flies
The greatest effect of curcumin observed was a 75% increase in lifespan with an intermediate dose of curcumin – from fewer than 10 days to more than 15 days on average, in one of the Alzheimer’s fruit fly models.
As all the different types of flies got older they became less active. Again, the effect of curcumin depended on the type of fruit fly tested:
- curcumin reduced activity slightly in normal flies
- curcumin had no effect on the activity one of the Alzheimer’s model fly strains
- the other four Alzheimer’s model fly strains all showed some increase in activity with curcumin, but the extent of the increase varied
The Alzheimer’s model fruit fly strain that showed the greatest increase in lifespan did not show the greatest increase in activity.
The researchers found that curcumin did not decrease the build up of insoluble deposits of amyloid beta in the brains of the fruit flies. However, curcumin sped up the soluble amyloid beta sticking together to form larger bundles called fibrils.
How did the researchers interpret the results?
The researchers concluded that curcumin reduces the toxic effects of amyloid beta or tau protein in the brains of genetically engineered fruit fly models of Alzheimer’s disease.
Curcumin is found in the bright yellow spice turmeric, which is commonly used in curries. This study has shown that curcumin can improve lifespan and activity in some genetically engineered fruit fly models of Alzheimer’s disease.
It is worth noting that this effect was not seen in all of the genetically engineered fruit fly models of Alzheimer’s disease, and that some fruit flies, including the normal ones, actually showed reduced lifespan with curcumin.
Chemicals showing beneficial effects and sufficient safety in animal studies also need to be tested in humans before we can know what their true effects on a disease are. Sadly, the promising effects of many chemicals seen in animals are not replicated in humans.
Despite what the papers have reported, this study cannot tell us whether a weekly curry will stave off Alzheimer’s or any other forms of dementia. However, it is worth noting that a high-fat diet is associated with some forms of dementia.
Analysis by Bazian.