It has taken 400 years but scientists have finally demonstrated what herbalists have long believed: sage is a tonic for the brain. Oil derived from the herb improved the memory of healthy young adults given a list of words to recall.

The Medicinal Plant Research Centre at Newcastle and Northumbria universities (both in UK) tested a group of 44 adults aged between 18 and 37. Some were given capsules containing sage oil while others received a placebo capsule of sunflower oil.

Those who took the sage oil performed consistently better, remembering more words than those who had the placebo.

Herbalists have been recommending sage since the 16th century. In 1597 John Gerard wrote: 'It is singularly good for the head and brain and quickeneth the nerves and memory.' Part of a 1652 description of sage by Nicholas Culpepper reads: 'It also heals the memory, warming and quickening the senses.'

Nicola Tildesley, chief researcher on the project - published in the journal Pharmacology, Biochemistry and Behaviour and funded by Oxford Natural Products -said: 'This proves how valuable the work by the old herbalists is, and that they shouldn't be ignored because they were writing centuries ago.'

But the finding is unlikely to be of use to exam candidates. Although sage enhanced immediate memory, it did not have the same effect when they were tested after 20 minutes.

The herb is already being investigated as a potential treatment for Alzheimer's disease, the most common form of dementia, which affects an estimated 10 million people worldwide.

This follows earlier work by the same team which showed that sage inhibits an enzyme called acetylcholinesterase (AChE). AChE breaks down the chemical acetylcholine, which has an important role in memory.

Alzheimer's is accompanied by a drop in levels of acetylcholine. Scientists think a combination of chemicals in sage oil have an effect on AChE. It is also thought to possess antioxidant, anti-inflammatory and hormone-like properties believed to be of value in treating Alzheimer's.

Results from a new trial testing the effect of sage on Alzheimer's patients are expected shortly.

Sage is a member of the mint family and has traditionally been used as a herb of purification. In the 14th century, eating three leaves a day was supposed to 'dispel the evil aire' all day long.

In ancient Greece, Theophrastus classified sage as a 'coronary herb' because it flushed disease from the body and relieved strain on the heart.

Another use for the herb was as a beauty product. The Greeks made a sage tea that was drunk or applied to the body to improve the skin.