Nicotine-based drugs may help delay the moment a person with dementia has to enter a care home, say researchers.
Nicotine has toxic effects, and carries a strong risk of addiction, but scientists have shown it can also boost learning, memory and attention.
The effect is small, but it may help give dementia patients up to six extra months of independent living.
A team at King's College London have demonstrated the positive effects of nicotine in experiments on rats.
"It may be possible for medicinal chemists to devise compounds that provide some of the beneficial effects of nicotine while cutting out the toxic effects"
Professor Ian Stolerman
Institute of Psychiatry
They showed that nicotine boosted the animals' ability to carry out a task accurately - particularly when they were also distracted.
When able to give full concentration, the animals responded correctly to stimuli about 80% of the time. Nicotine boosted the accuracy rate by about 5%.
However, when distracted, the animals' success rate fell to about 55%. In this case nicotine brought it back up to around the 85% level.
Biochemical mechanisms
The King's team, based at the Institute of Psychiatry, studied the mechanisms which underpin the effects produced by nicotine.
They showed how proteins on the surface of cells respond to the compound, and pinned down the role of several key chemicals in the brain, including dopamine and noradrenaline.
It transpired that there are only subtle biochemical differences in the way nicotine stimulates the brain, and triggers addiction.
Several nicotinic drugs are already in development, but the King's team hopes its work will speed up the discovery of agents which give the brain a bigger boost than nicotine, with longer lasting effects.
Lead researcher Professor Ian Stolerman said: "Nicotine, like many other drugs, has multiple effects, some of which are harmful, whereas others may be beneficial.
"It may be possible for medicinal chemists to devise compounds that provide some of the beneficial effects of nicotine while cutting out the toxic effects."
Professor Stolerman stressed that the positive effects produced by nicotine were small, and would be of no benefit to most people.
However, he said they could potentially make a difference to dementia patients.
He added that the "cognitive boost" that many smokers experience from nicotine may contribute to the pleasure they get from their habit.
'Don't smoke'
Professor Clive Ballard, of the Alzheimer's Society, said: "Although nicotine has therapeutic qualities, when it is absorbed through smoking the health risks outweigh the benefits.
"Smoking increases risk of vascular dementia, the second most common form of dementia and is associated with a number of other health risks.
"More research is now needed to find a safe and effective treatment for dementia, with the potential benefits of nicotine, but without the health risks."
Rebecca Wood, of the Alzheimer's Research Trust, agreed that people should not be tempted to smoke to try to ward off dementia. She said the best way to minimise risk was to eat a balanced diet and exercise regularly.
Professor Stolerman said there was no reason to believe that nicotine or smoking reduced the risk of getting dementia - it only helps to reverse symptoms.
It is estimated that 700,000 people in the UK live with dementia.
The research will be presented to a Federation of European Neuroscience Societies conference in Geneva.
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