What does the latest study show?
To see if resveratrol could delay the progression of Alzheimer's disease in people , Scott Turner at Georgetown University Medical Centre in Washington DC and his team gave 119 people with mild to moderate symptoms of the disease either a gram of synthesised resveratrol twice a day in pills for a year, or a placebo.
Over the course of the study, those in the placebo group showed typical signs of Alzheimer's progressing, including a decline in the level of amyloid beta protein in their blood -- thought to be a sign that this compound was being taken from their blood and deposited in their brains.
Did the resveratrol make any difference to brain function?
This study was designed to test the safety of taking large doses of resveratrol, rather than look at whether it works. As such, the study is too small to detect any meaningful effect that it might have had on brain function. But Turner says they did see a slight improvement in one measure of cognitive function, although this wasn't statistically significant. A larger study may find a stronger result.
Is amyloid a good indicator of Alzheimer's disease?
Alzheimer's is typically characterised by the build-up of amyloid plaques in the brain, so it is often used as a biomarker for the disease. But questions remain over the role of amyloid in the disease -- does it cause the condition or is it just a symptom? We won't know how informative amyloid levels are until we find a successful way of stopping or slowing Alzheimer's, says Neil Buckholtz of the NIH National Institute on Aging in Bethesda, Maryland, which funded this study.
* Resveratrol exhibits therapeutic potential for cancer chemoprevention as well as cardioprotection.
"It sounds contradictory that a single compound can benefit the heart by preventing damage to cells, yet prevent cancer by causing cell death, said Brown. "The most likely explanation for this, still to be rigorously proved in many organs, is that low concentrations activate survival mechanisms of cells while high concentrations turn on the in-built death signals in these cells."
* Resveratrol may aid in the prevention of age-related disorders, such as neurodegenerative diseases, inflammation, diabetes, and cardiovascular disease.
"The simplest explanation is that resveratrol turns on the cell's own survival pathways, preventing damage to individual cells," said Brown. "Further mechanisms help, including removing very reactive oxidants in the body and improving blood supply to cells."
* Low doses of resveratrol improve cell survival as a mechanism of cardio- and neuro-protection, while high doses increase cell death.
"The key difference is probably the result of activation of the sirtuins in the nucleus," said Brown. "Low activation reverses age-associated changes, while high activation increases the process of apoptosis or programmed cell death to remove cellular debris. Similar changes are seen with low-dose versus high-dose resveratrol: low-dose resveratrol produces cellular protection and reduces damage, while high-dose resveratrol prevents cancers."
Does this mean we should drink more wine?
"You can't possibly consume enough resveratrol from food sources to reach the doses that were used in the study," says James Hendrix, a scientist with the US charity Alzheimer's Association. Turner estimates someone would have to drink 1000 bottles of red wine a day to even come close.
"Nature did not design resveratrol to treat Alzheimer's disease, it designed it for some other reason that only a grape knows," says Hendrix. But the molecule is a good starting point, he says. Chemists should be able to tweak the structure to make more of the chemical reach the brain and to reduce the dose and side effects.
Until then, it's probably best to think of resveratrol and other dietary molecules as counteracting poor diet rather than preventing Alzheimer's.