Extract of a spice used in curry could help prevent rheumatoid arthritis and osteoporosis, US research suggests.
Turmeric adds flavour and colour to curries and other foods
Turmeric has been used for centuries in Asian medicine to treat inflammatory disorders and its extract can be found in western dietary supplements.
Now lab work by University of Arizona researchers, in Arthritis & Rheumatism, shows just how the spice's curcuminoid extracts have a therapeutic effect.
Experts say new drugs may be found, but eating more spices is unlikely to work.
The researchers said clinical trials were needed before turmeric supplements could be recommended for medicinal use.
Earlier work by the University of Arizona team showed turmeric could prevent joint inflammation in rats.
In their latest study, they set out to find exactly what ingredient in turmeric was having the anti-inflammatory effect.
They prepared extracts from the rhizome, or root of the turmeric plant, and compared them against the commercially available products that contain turmeric extracts.
A version of turmeric extract that was free of essential oils was found to most closely match the composition of the commercial supplements.
And it was this extract, containing curcumin, that was most effective at blocking the onset of rheumatoid arthritis in the rats.
The extract appears to work by preventing a protein that controls when genes are switched on or off from being activated in the joint.
Once the protein known as NF-KB is activated, it binds to genes and increases the production of inflammatory proteins, which attack the joints.
Dr Janet Funk and her colleagues believe their findings also suggest turmeric extract could treat other inflammatory disorders, including asthma, multiple sclerosis and inflammatory bowel disease.
The extract also blocked a pathway in the body linked to bone loss, suggesting it could treat osteoporosis as well.
Professor Robert Moots, professor of rheumatology at Liverpool University and spokesman for the Arthritis Research Campaign, said people with arthritis will have to wait to see if the study results in new treatments.
"It will come as no surprise if naturally occurring compounds have a drug-like effect," he said.
"I do not think there is any evidence that countries that eat a lot of turmeric have a lower frequency of rheumatoid arthritis. So simply eating more spices is not likely to be effective clinically.
"What is more likely is these results will lead to the targeted development of new compounds."
Dr Anne Barton, senior lecturer and honorary consultant rheumatologist at the University of Manchester said: "The findings are interesting but should be interpreted with some caution at this stage.
"Results of tests in animal models of arthritis are not always reproduced in human rheumatoid arthritis.
"As the authors point out though, there are a number of successful drug therapies that have been developed from plants."