A method to predict a middle-aged person's chance of developing dementia has been devised by scientists.
The idea is to have a simple tool to predict the risk for diseases
The test calculates risk by assessing factors such as blood pressure level, body mass index and cholesterol levels, along with age and education.
The work, published in the journal Lancet Neurology, is based on a Finnish study that revealed several midlife risk factors were linked to dementia.
A high-risk result, said the team, could encourage lifestyle changes.
The scientists used data from the Cardiovascular Risk Factors, Ageing and Dementia study.
This research assessed 1,409 middle-aged people from Finland and then looked at them again 20 years later for signs of dementia, including Alzheimer's disease and vascular dementia.
Scientists discovered that along with the known risk factors of age and a low-level of education, high blood pressure, high cholesterol and obesity also meant people had a higher chance of suffering from dementia.
Using these results, the team developed a score-based system to predict the likelihood of a middle-aged person developing dementia in later life.
Lead researcher Miia Kivipelto, from the Aging Research Center, Karolinska Institute in Sweden, said: "The idea is to have a simple tool to predict the risk for diseases, like you have for cardiovascular diseases or diabetes.
"But for dementia there has been nothing like this. The idea to put this information together and have an overall estimation for dementia risk is new."
The predictive test takes information about age, number of years spent in education, sex, body mass index, blood pressure level, cholesterol level, physical activity and genetic factors and assigns each with a risk score related to their association with dementia.
Then, combining these, the patient can be given an overall score, indicating the probability of them developing dementia.
Dr Kivipelto said: "We hope physicians could use this system to find people who are at a higher risk of developing dementia at later life."
Once these people have been identified, she added, they could be advised to change their lifestyle, or be given drugs, so as to lower their weight or blood-pressure levels.
"It is also an easy way to see how much you can do yourself to lessen your risk of dementia."
Rebecca Wood, chief executive of the Alzheimer's Research Trust, said: "It is remarkable that one can start to protect oneself from dementia that much earlier.
"To be able to identify a group of people at higher risk and who might be able to introduce lifestyle changes to reduce their risk is very exciting.
"The proposed test is still a somewhat blunt instrument, because it picks up too many people who may not develop dementia so much more work is needed to improve and validate its results."
Professor Clive Ballard, director of research at the Alzheimer's Society, said: "New developments that encourage living a healthy life style are an important step towards combating dementia.
"We recommend that people take regular exercise; eat healthily; make sure they get their blood pressure checked and take part in social activities."
The Mental Health Foundation said that the general public must take responsibility for their diets if they are to avoid dementia in later life.