The new study, published in the November issue of the journal Arthritis & Rheumatism (Vol. 54, pp. 3452-3464), is said to be the first to document the efficacy of curcumin-containing extracts for anti-arthritis activity in vivo, as well as demonstrating that the extracts studied are analogous with commercially available turmeric dietary supplements.
"Just as the willow bark provided relief for arthritis patients before the advent of aspirin, it would appear that the underground stem (rhizome) of a tropical plant [turmeric] may also hold promise [against] joint inflammation and destruction," wrote lead author Janet Funk from the University of Arizona in Tucson.
Approximately seven million people in the UK alone are reported to have long-term health problems associated with arthritis. Around 206 million working days were lost in the UK in 1999-2000, equal to £18bn (€26bn) of lost productivity.
The researchers compared the chemical composition of experimental extracts (from turmeric powder, San Francisco Herbs, Spices and Teas) with those of commercially available over the counter turmeric dietary supplements. Two experimental extracts were prepared - a crude extract with 34 per cent curcuminoids and containing essential oils, and an extract with 41 per cent curcuminoids and no essential-oils.
Funk and her co-workers report that the majority of the over-the-counter supplements were also free of essential oils and had curcuminoids contents ranging from 1.8 to 33.7 per cent.
Female rats were used to test the efficacy of the extracts in vivo. The rats were injected with either a saline solution or an arthritis-inducing solution. The animals were then injected with one of the turmeric extracts or a control solution, and joint inflammation measured.
Initial results showed that a version of turmeric extract that was free of essential oils had the most significant impact on arthritis and most closely matched the composition of commercially available supplements.
Cartilage destruction in the tibia of the rats was reduced by 66 per cent, and thigh bone mineral density (BMD) destruction was also reduced by 57 per cent, compared to the control solution.
The researchers, funded by the Office of Dietary Supplements and National Center for Complementary and Alternative Medicine of the National Institutes of Health, reported that an effective dose in rats that would be equivalent in humans to 1.5 milligrams per day of a portion of the turmeric root that makes up three per cent of dried turmeric powder.
A mechanistic study showed that the turmeric extracts appeared to work by inhibiting the protein, NF-kappaB, known to be play a key role in some inflammatory pathways.
"Given the critical role of NK-kappaB as the 'master switch' in innate immunity, these in vivo experiments… provide proof-of-concept for the us of this botanical in other diseases triggered by inappropriate activation of NF-kappaB-regulated inflammatory pathways, including inflammatory bowel disease, asthma, and multiple sclerosis," said the researchers.
They noted, however, that the research did not exclude the possibility that the spice extract may also block other inflammatory processes that are parallel to the NF-kappaB process.
"Before turmeric supplements can be recommended for medicinal use, clinical trials are clearly needed to verify/determine whether… adequate doses of well-characterized turmeric extracts can indeed prevent/suppress disease flares in RA [rheumatoid arthritis] patients, as well as to explore any potential benefits of turmeric dietary supplements in the prevention or treatment of more common forms of arthritis in the general population," concluded the researchers.
Professor Robert Moots, from Liverpool University and spokesman for the British-based charity, Arthritis Research Campaign said that it was not surprising that naturally occurring compounds had similar effects to drugs.
"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," he said in a statement