Good cholesterol could be the key to long term brain health and the prevention of dementia in women, new research has revealed.

The findings come as two thirds of people living with dementia are women and confirmation from the Australian Bureau of Statistics that it is now the leading cause of death for women.

Two new University of Melbourne studies show cholesterol levels alter the structure of grey and white matter in the brain, which determines the likelihood of decay to the brain.

The first study, published in the journal Brain Imaging and Behaviour, found the volume of grey matter in a woman's brain at 60 predicts her memory performance at 70.

The second study, published in the same journal, found women with normal levels of 'good' cholesterol had less white matter damage in their brain when tested again a decade later.

Researchers found women with white matter changes were worse at planning and organisation tests and those with grey matter volume loss had worse memory as they aged.

So the studies showed that maintaining healthy levels of cholesterol impacted on the structure of the brain directly.

A co-author of both and the director of the University of Melbourne's Women's Healthy Ageing Project, Professor Cassandra Szoeke, said the research showed healthy blood vessels (with good cholesterol in them) reduced the risk of cognitive decline and disease.

"This aligns with our knowledge that regular physical activity, normal blood pressure and maintaining normal levels of HDL ('good') cholesterol are all associated with better cognition," she said.

Good cholesterol refers to high-density lipoprotein, as opposed 'bad' cholesterol or low-density lipoprotein.

Not smoking, being a healthy weight and doing regular exercise contribute greatly to achieving good cholesterol, as well as eating fatty fish, olive oil, coconut oil and purple vegetables.