The leaves of the ancient Ginkgo biloba tree can help with memory loss and circulatory disorders. Anne Woodham investigates

Ginkgo biloba is one of the best-known and widely available herbal remedies, particularly popular among people over 50 who are anxious about possible memory lapses.

Chinese herbalists traditionally used ginkgo to treat asthma, bronchitis, bladder infections and brain disorders (Ginkgo nuts are a kidney 'yang' tonic to increase sexual energy and prevent premature ejaculation). In Europe and the US, scientific studies suggest that ginkgo leaf extracts can benefit failing memory, Alzheimer's disease, age-related dementias and circulatory disorders such as Raynaud's disease by improving blood flow to the brain, heart, limbs, ears and eyes. It can also help erectile dysfunction by improving blood flow to the penis.

The name ginkgo is thought to come from the Chinese word sankyo or yin-kuo, meaning 'silver fruit.' Biloba, the European species name, refers to the unique two-lobed leaves that resemble a duck's foot. Ginkgo is also known as 'maidenhair tree' or 'forty-coin tree.' It is among the oldest living tree species, often called a 'living fossil.'

The last Ice Age almost wiped out the tree , but it survived in China and parts of Asia where it has been used for food and medicine for 4,000 years. Nowadays it grows in Europe, North America and Australia, and is often found in city parks and streets because of its extreme hardiness in withstanding pollution, low sunlight, and it?s resistance to disease and insects. Many trees live to 1,000 and even 2,000 years, and a few are thought to be nearly 4,000 years old.

Ginkgo contains antioxidant compounds - flavonoid glycosides and terpenoids such as ginkgolides, bilobalides and quercetin - that scavenge chemicals known as 'free radicals' that cause cell damage and hasten ageing. The central nervous system and brain are especially susceptible to this kind of damage.

These compounds also appear to stabilise cell membranes and make blood vessel walls and red blood cells more flexible, so that blood flows more freely in the tiny capillaries that feed the further reaches of the brain, limbs and other extremities. Oxygen in the blood enhances brain functions like memory, concentration and problem-solving ability. When blood flow to the brain is weakened, as in the elderly, these functions are impaired.

Ginkgolides benefit healthy blood circulation by inhibiting the effects of a blood clotting substance called platelet activating factor (PAF). While our bodies need PAF for certain functions, too much of it has been linked to allergies, asthma and cardiovascular diseases such as stroke.

Ginkgo and Alzheimer's

In Germany, where numerous scientific trials of the plant have been carried out, ginkgo leaf extract is one of the most popular herbal medicines. But it was the results of a multi-centre study of 202 patients published in the prestigious Journal of the American Medical Association in October 1997 that really put ginkgo on the international map. This showed that the leaf extract could delay the progression of Alzheimer's by six months to a year.

Whether ginkgo biloba makes a difference to cognitive function in healthy people is another question. Studies, including several in the UK, show that it may improve working memory, especially in those aged 50-59, but has little effect on concentration. Any benefits will probably take at least four-six weeks (sometimes 24 weeks) of treatment to become apparent.

Ginkgo seems to be safe and well-tolerated by most people. Side effects are rare, but mild gastrointestinal upsets, headache and dizziness have been reported. Very large doses can cause nausea, vomiting, diarrhoea and restlessness.

The extract is available as tablets, capsules or tinctures. Look for a product standardised to a 24 per cent concentration of ginkgo flavone glycosides. In clinical studies, the effective dose was 40 mg of standardised ginkgo extract three times a day, a total of 120 mg.

Always follow instructions on the package and consult your doctor before using ginkgo if you are taking prescription drugs, particularly anticoagulant or vasodilator medication.