Long-term use of ginkgo biloba extract does not reduce the risk of Alzheimer’s disease in older people, according to a new study.

The largest ever Alzheimer’s prevention study in Europe, published Wednesday in Lancet Neurology, examined the popular extract that comes from a unique tree species thought to aid in improving memory, dementia and Alzheimer's disease.

French researchers based their findings on a randomized placebo-controlled blind study of about 3,000 people over nearly five years.

Adults over the age of 70 who had complained of memory problems were randomly put in two groups; one group given a twice per day dose of 120 mg of ginkgo biloba and one given a placebo.

Participants were followed up by primary-care physicians and in expert memory centres between March 2003 and November 2004.

The study involved 2854 participants, 1406 were given at least one dose of ginkgo biloba and 1414 were given at least one dose of a placebo. By 2004, 61 people in the gingko group were diagnosed with probable Alzheimer’s disease and 73 were diagnosed in the placebo group.

Risks were not proportional over time and incidence of adverse effects and events was basically the same between the groups. In the ginkgo group 76 died compared with 82 participants in the placebo group.

There were 65 people in the ginkgo group who suffered a stroke and 60 in the placebo group. Other cardiovascular events were also similar among both groups.

Researchers concluded that ginkgo was not effective in reducing the onset of Alzheimer’s dementia as was once thought.

The study mentioned that the main limitation was that the number of dementia events was much lower than expected to begin with, which lead to a lack of statistical power to detect such effects.

Gingko biloba extract contains flavonoid glycosides and terpenoids that are often believed to aid in cognitive function. It has been used in Chinese medicine for hundreds of years.