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Posted on Dec 20, 2004, 2 p.m.
By Bill Freeman
Lemon, lilac and leather are three of 10 odours that can be used to tell whether a person is likely to develop dementia, according to US scientists. A Columbia University team tested the odours on 150 people with minimal to mild cognitive impairment. Those who went on to develop Alzheimer's disease performed poorly in terms of identifying the 10 smells.
A Columbia University team tested the odours on 150 people with minimal to mild cognitive impairment.
Those who went on to develop Alzheimer's disease performed poorly in terms of identifying the 10 smells.
Experts welcomed the study, but said such tests should not used in isolation as a test for Alzheimer's. 
The researchers pinpointed 10 odours to test
Telling smells
The odours also included clove, smoke, menthol, pineapple, soap, strawberry and the artificial 'egg-like' odour that is added to natural gas, .
The study was described to the American College of Neuropsychopharmacology.
Doctors have known for some time that smell is one of the first things to go when someone develops dementia.
Although it is impossible to diagnose Alzheimer's disease with 100% certainty whilst a person is alive, memory tests, genetic tests and brain scans can give an idea of whether this form of dementia is likely.
More recently, smell tests have been added to the tools used to predict dementia risk.
Dr Davangere Devanand and colleagues set out to determine which odours are best to use.
They tested 150 people with minimal to mild cognitive impairment (MCI).
In this condition, people have memory problems that are hard to discern from those found with normal ageing.
Some people with MCI will remain healthy, but others will go on to develop full-blown dementia.
The team tested the volunteers' ability to distinguish between different odours once a year for five years.
The Alzheimer's Society is funding research into a lavender smell test
Compared with the MCI volunteers who did not go on to develop full-blown dementia and 63 healthy elderly people, those with MCI who developed Alzheimer's performed poorly on the test.
Ten odours were particularly good markers of Alzheimer's risk and the results based on these markers tallied with memory test results and brain scan signs of dementia.
Dr Devanand said the test could help spot Alzheimer's sooner.
"Early diagnosis is critical for patients and their families to receive the most beneficial treatment and medications," he said.
Professor Tim Jacob, an expert in smell at Cardiff University, said the smell test was a good idea, but it was essential that it was used in conjunction with other tests for Alzheimer's and backed by expert advice and support.
Future tests
"Smell can be affected by a great many things - if you have a cold, for example. Or before a meal, your sense is more acute than after a meal.
"In the US, you can buy a self-testing Alzheimer's kit based on smell, which I think is unethical and horrifying."
He said the test could be improved by quantifying how well a person is able to discern odours. He is currently trying to do this.
Dr Susanne Sorensen, head of research at the Alzheimer's Society, said: "The physician relies on several tests to reach a best clinical judgement.
"A test that is quick to carry out and non-invasive would, if proven to work, be a significant step forward."
The Alzheimer's Society is funding a study at Oxford University looking into a person's ability to smell lavender.
Dr Steve DeKosky, chairman of the Medical and Scientific Advisory Panel for Alzheimer's Disease International, said: "Although tests for smell are usually abnormal in Alzheimer's, they have not been reliable enough to help with diagnosis, in part because many older people, and a number of late-life brain diseases also have problems with naming odours.
"This study...may help make the diagnosis earlier and perhaps more accurate."
