It will be the first to test gingko as a treatment for those who are still living in the community and are being treated by their GP. Previous trials have concentrated on patients receiving hospital care, where the condition is often more advanced.

We believe gingko may prove more effective if prescribed in a community setting, where patients symptoms are usually less severe, says Dr James Warner, a psychiatrist from Imperial College London and St Marys Hospital, who is leading the study. This trial will help us to find out whether with gingko its a case of the sooner the better, for patients who may benefit from taking it.

Gingko is believed to cause blood vessels to dilate, improving blood flow to the brain, and to thin the blood, making it less likely to clot. Gingko may also have antioxidant effects, protecting nerve cells against biological rusting.

All of these effects would suggest that gingko might slow down a degenerative process such as dementia, says Dr Warner.

It is estimated that 700,000 people in the United Kingdom are affected by the condition, 60 per cent of whom are diagnosed with Alzheimers disease. Patients might occasionally misunderstand who or where they are, forget peoples names or how to get home.

Gingko could provide a cheaper alternative to conventional medicines, with fewer of the potential side effects such as nausea, loss of appetite, tiredness and diarrhoea. A quality gingko extract taken from the Gingko biloba tree costs around £200 for a years supply. It is currently available over the counter in the UK, most European countries and the United States.

Conventional medicines for memory loss are based upon a class of drugs known as cholinesterase inhibitors, which cost around £1,000 a year, and prescription of these drugs is restricted. Some patients also benefit from therapies such as music therapy, aromatherapy and reminiscence therapy, which keep the environment stimulating and encourage the use of the brain.

Participants on the double-blind trial will continue to take their conventional medicines for age-associated memory loss. For six months they will be given 60mg of gingko extract or a placebo twice daily. Participants will also receive up to three visits of one and a half hours where researchers will examine each individuals cognitive functioning, their memory, quality of life and behaviour.

Robert McCarney, research associate on the study adds We are now recruiting individuals living in or around London and the home counties, aged over 55 and whom their GP suspects may have dementia. Anyone interested in finding out more about the study should telephone 020 7886 7697.

For general information relating to age-associated memory loss or Alzheimers disease, contact The Alzheimers Society helpline on 0845 300 0336.

The study is being carried out by Imperial College London in collaboration with the London School of Hygiene and Tropical Medicine, the Royal London Homeopathic Hospital and University College London. The Alzheimers Society is funding the research.

Gingko facts

Fossilised remains of the ancient tree have been found dating back 200 million years. It has been used in traditional Chinese medicine for at least 5,000 years. In Germany, gingko is of the top 10 prescription medicines for the treatment of circulatory problems. Germans spent 280 million dollars on gingko in 1993. Four gingko trees survived the atomic bomb in Hiroshima in August 1945, leading local people to name the tree the bearer of hope. The tree inspired Goethes poem Gingko Biloba. The gingko tree can grow up to forty metres tall and can achieve a spread of nine metres.