One in two women will develop dementia or Parkinson’s disease, or have a stroke, in their lifetime, new research suggests.

About a third of men aged 45 and half of 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 preventive 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 – the generic term for a range of symptoms that can be seen in someone with Parkinson’s disease – 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.

“These are the three most common neurological diseases in the elderly population and also some of the most feared,” said Silvan Licher, one of the authors of the study, who said they embarked on the study to show the burden of neurological diseases on elderly people. In middle age, there is a great deal of focus on heart disease and cancer, but diseases of the brain in later life get less attention and are less researched. For people over 85, dementia is the greatest risk, he said.

Many people suffer from more than one disease in later life. “We noticed that there is much overlap between them,” said Licher. “People do not just have one disease in later life but can have two or three at the same time.”

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.

Routledge said it was “crucial” that efforts to find a drug that could delay the onset of dementia symptoms were increased. “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,” she said.

“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.”