A simple blood test could spot Alzheimer’s at least five years before symptoms start to show.

The test’s creator hopes it will be in widespread use within three years.

Quicker detection of the disease would allow earlier treatment and, with the help of new drugs, those who test positive may never fully develop it.

Those given early warnings could also take preventative measures, such as changing their diet and taking more exercise.

Alzheimer’s and other forms of dementia affect more than 800,000 Britons. The figure is set to double in a generation.

Currently, sufferers are only diagnosed after the disease has already caused significant damage to the brain.

But the new test aims to detect signs of Alzheimer’s years earlier by distinguishing between mere forgetfulness and the more dangerous memory lapses that signal dementia in its earliest stages.

Spotting Alzheimer’s early on would have ‘immense’ benefits for the elderly, the test’s inventor said last night.

Professor Matej Oresic made the breakthrough after analysing the blood of 226 men and women in their late sixties and seventies and then tracking their health for an average of five years.

At the start of the study, 37 had already been diagnosed with Alzheimer’s; of the others, 46 did not have any memory problems but 143 were suffering from forgetfulness.

By the end of the study, 52 of that 143 had also been diagnosed with Alzheimer’s.

Comparing their blood samples with samples from those who were still merely forgetful revealed clear differences in the concentration of three metabolites – chemicals produced by reactions in the body.

Working out how these chemicals relate to the progression of Alzheimer’s could help develop new treatments for the disease. Testing for them in elderly people suffering from forgetfulness could lead to valuable early warnings of the onset of dementia, the journal Translational Psychiatry reports.

Those found to have memory problems related to Alzheimer’s could do mental and physical exercises and change their diet in an attempt to keep their brain healthy for as long as possible.

Professor Oresic, of the VTT Technical Research Centre of Finland, said delaying the onset of Alzheimer’s in older people ‘is almost as good as preventing it’, adding: ‘A delay of even a couple of years would immensely improve quality of life.’

He said that more work is needed to show just how accurate his test is – but he hopes the kit will be in small-scale use within a year, and widely used in two or three.

Dr Simon Ridley, head of re- search for the charity Alzheimer’s Research UK, said Professor Oresic’s work had seen ‘prom- ising early results’.

He added that the chemicals produced by the billions of reactions that occur in the body present a ‘gold-mine’ of potentially useful information for scientists.

If research on such chemicals leads to the development of drugs that can stop the progression of Alzheimer’s, those who receive an early positive on Professor Oresic’s test may never go on to fully develop the disease after all.