Half of women will develop dementia, Parkinson's disease or have a stroke in their lifetime, new research suggests.
About a third of men aged 45 and one in two women of the same age are likely to go on to be diagnosed with one of the conditions, according to a study of more than 12,000 people.
The researchers, from the University Medical Center Rotterdam, in the Netherlands, said preventative measures could "substantially" reduce the burden of the illnesses.
The findings have been published in the Journal of Neurology, Neurosurgery, and Psychiatry.
The health of 12,102 people was monitored between 1990 and 2016, with all participants initially under the age of 45.
During this period 1,489 were diagnosed with dementia and 263 with parkinsonism, while 1,285 had a stroke.
The overall risk of a 45-year-old later developing one of the three conditions was 48% for women and 36% for men, the researchers said.
Dementia was of greatest concern for women, who at 45 years old had a 25.9% risk of going on to develop the condition, compared with 13.7% for men.
Dr Carol Routledge, director of research at Alzheimer's Research UK, said: "This large study underscores the enormous impact that neurological illnesses have across society and how women are disproportionately affected, particularly when it comes to dementia."
Those diagnosed with one of the three conditions were found to have a higher prevalence of high blood pressure, abnormal heart rhythm, high cholesterol and Type 2 diabetes at the start of the monitoring period.
"These findings strengthen the call for prioritising the focus on preventative interventions at population level which could substantially reduce the burden of common neurological diseases in the ageing population," the authors said.
They estimate that if onset of dementia, parkinsonism and stroke was delayed by one to three years, the remaining risk of developing the conditions could be cut by 20% among 45 year olds and more than 50% in those older than 85 years old.
Dr Routledge (pictured) said it was "crucial" that efforts to find a drug which can delay the onset of dementia symptoms were increased.
She added: "For most of us, our individual risk of illnesses like dementia is not set in stone and there are things we can all do to help maintain a healthy brain.
"The best current evidence suggests that eating a balanced diet, controlling our weight, staying physically active, not smoking, only drinking within the recommended limits and keeping blood pressure and cholesterol in check are all associated with better brain health into old age."
Claire Bale of Parkinson's UK said: "Our recent analysis found that Parkinson's is set to rise steeply to 170,000 by 2025 due to our growing and ageing population. Although it's important to point out that, unlike dementia, women are actually at slightly lower risk of developing Parkinson's than men.
"We urgently need to invest more in research to develop better treatments to help those living with these devastating conditions, and ultimately to find ways to prevent people from developing them in the first place."
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