The quality of the active ingredient in ginkgo supplements appears to have dropped significantly in the last three years, according to tests done by ConsumerLab.com.
The organisation reported that only 22 per cent of the Ginkgo biloba supplements it tested met the quality standards compared to 75 per cent of the products tested in late 1999.
Ginkgo, which is used to improve cognitive functioning, remains a top-selling herb in the US, although sales fell by 29 per cent to $47 million in the past year according to market research firms SPINS and ACNielsen.
Ginkgo supplements are generally made from a highly concentrated leaf extract. Products that have been effective in clinical trials contain defined amounts of special compounds from the leaf. Many products on the market claim to be standardized only to total amounts of these compounds and not to the individual compounds.
ConsumerLab.com said it found most ginkgo products (nine were tested) to contain less than one-fifth of the expected amount of bilobalide - a compound that may play a particularly important role in the effectiveness of ginkgo.
"While consumers are often told to look for 'standardized' ginkgo, the standards used by many manufacturers do not measure up to those used in clinical studies," said Dr Tod Cooperman, president of ConsumerLab.com. "It's like selling a car with only one cylinder: it's still a car, but it is not likely to perform well. This may also help explain why sales of ginkgo have been falling."
ConsumerLab.com added that the findings also pose a challenge to the FDA's proposed rules for the labeling of supplements which do not clearly define standards for herbal ingredients.
A more recently introduced supplement for improving cognitive functioning (particularly in Alzheimer's patients) called huperzine A was also tested in the recent review. All of the huperzine products (four in total) contained the labeled amount of the ingredient, but one was found to be high in lead.