Scientists at the Heart Research Institute say they have made a major breakthough by finding the definitive relationship between dementia and high levels of cholesterol for the first time.

The researchers say the findings are significant, because they mean future tests to calculate a person's risk from dementia can be performed through blood tests.

The scientists examined the data from 17 global studies that included more than a million patients under the age of 65.

The Institute's Dr Ashish Misra said the findings were exciting and a 'game-changer' because it was the first definitive link between levels of cholesterol and dementia.

"This is the first time we've been able to say categorically that there's a direct link between what we eat and our cognitive decline," he said.

Until now we haven't known high cholesterol was a risk factor for dementia, but we've found a link: "bad" cholesterol aggregates a protein called tau between neurons, which cross the blood-brain barrier, and can lead to dementia," Dr Misra said.

Cholesterol is used by the body to make hormones and aid digestion, but too much cholesterol from a diet high in sugar and fat will lead to an imbalance of lipid levels in the blood, causing complications.

High levels of cholesterol can lead to the accumulation of plaque along artery walls, increasing the risk of stroke.

"Unfortunately, there's no magic drug to get rid of the plaque on your arteries. We need to learn to live with it and help it dissolve over time through improved diet and a healthy lifestyle."

Dr Misra said the discovery will lead to much better identification of early warning signs for dementia, which will give people the chance to work on their risk factors including diet and exercise.

Evidence has shown that the initial effects of dementia often begin 10 to 20 years before clinical symptoms begin to present, and that 40 per cent of the risk of developing it can be attributed to modifiable risk factors.

Dr Misra said simple and cost effective tests can be performed by doctors on people in their 50's, so at-risk patients can work on improving their diet as a way of managing cognitive decline.

The number of people living in Australia with dementia is around 487,500. For the population aged above 65, it equates to 84 sufferers per 1000 people.

The Australian Institute of Health and Welfare says that figure is expected to climb higher in the coming years due to the nation's aging population.

There are projections the number of Australians living with dementia will more than double by 2058.