Patients with Alzheimer's disease have been given fresh hope as scientists discover that off the shelf vitamin B supplement halts memory loss.

Researchers have discovered that high doses of Vitamin B3, which costs as little as £4 over the counter, could have a dramatic effect on the onslaught of the progressive disease.

The breakthrough by US scientists could mean a cheap and easily obtainable treatment for the 417,000 or so sufferers in the UK.

The supplement is thought to reduce the build up of "tangles" in the brain that cause cell death and dementia and could also boost the general performance of neurons in the mind.

The researchers at the University of California found that high doses of a common type of the vitamin, known as Nicotinamide, significantly reduced memory loss in mice with the disease.

Now they are holding clinical trials to see if the supplement has the same effect on humans.

"Nicotinamide has a very robust effect on neurons," said Kim Green, a scientist at the University of California and lead author of the study. "Nicotinamide prevents loss of cognition in mice with Alzheimer's disease, and the beauty of it is we already are moving forward with a clinical trial."

Hope has been high for a while that the use of vitamin B could be beneficial to sufferers of dementia including Parkinson's and Huntingdon diseases.

But previous research by the same university has provided conflicting results about its usefulness and only last month a study using B6, B12 and B18 failed to show any improvements.

But the latest research, published in the Journal of Neuroscience, suggests that Nocotinamide may be different.

For the trials around 25 volunteers, all over 50 years old with early signs of Alzheimer's Disease, will be given extremely high doses of the vitamin - around 1,500 mg or 15 tablets - twice a day for six months.

Another 25 will be given a placebo.

Researchers hope the vitamin might block the action of a protein called phosphorylated tau, which builds up in Alzheimer's disease, clogging up the brain and suffocating the cells.

In mice, nicotinamide was shown to lower the levels of tau. The vitamin also strengthened microtubules along which information travels in brain cells, helping to keep neurons alive and further preventing symptoms in the mice, which were genetically engineered to develop Alzheimer's.

In the study, Green and his colleague, Frank LaFerla, added the vitamin to drinking water fed to mice. They tested the rodents' short-term and long-term memory over time using water-maze and object-recognition tasks and found that treated Alzheimer's mice performed at the same level as normal mice, while untreated Alzheimer's mice experienced memory loss.

The nicotinamide, in fact, slightly enhanced cognitive abilities in normal mice.

"This suggests that not only is it good for Alzheimer's disease, but if normal people take it, some aspects of their memory might improve," said LaFerla, UCI neurobiology and behaviour professor.

"Microtubules are like highways inside cells. What we're doing with nicotinamide is making a wider, more stable highway," Green said. "In Alzheimer's disease, this highway breaks down. We are preventing that from happening."

Even though nicotinamide is found naturally in beef, pork, chicken, wheat flour, maize flour, eggs and milk, the amounts that would have to be eaten would be enormous to get the same effect as the pills.

There is also a danger that the large amounts of the vitamin, which is used to reduce anxiety and sells in vast quantities (550million bottles a year), will cause skin flushes or even liver damage.

Rebecca Wood, chief executive of the Alzheimer's Research Trust, said: "This research indicates that vitamin B3 could improve memory function in mice with Alzheimer's. These are exciting findings, but until the results from the human clinical trial are announced, people should be wary about changing their diet or taking supplements. In high doses vitamin B3 can be toxic.

"The Alzheimer's Research Trust is funding research into vitamins that could give a protective effect to try to identify ways of reducing people's risk of developing Alzheimer's. It can also help increase our understanding of the disease and ways to develop new treatments.

"We await the results of this exciting clinical trial."