Suffering two or more chronic health problems in midlife more than doubles the risk of dementia, research suggests.
The new research, published in the BMJ, found that the risk is greater when these types of conditions develop at a younger age, such as the mid-50s, rather than later in life.
For the study, experts looked at those having two or more chronic health conditions when they were aged 55, 60, 65 and 70.
From the group of 10,095 British men and women taking part in the Whitehall II Study, 7 per cent had two or more conditions at the age of 55, rising to 32 per cent at age 70.
A total of 639 cases of dementia occurred over a typical 32 year follow-up.
After adjusting for factors such as socio-economic status, diet and lifestyle, having two or more conditions at the age of 55 pushed up the risk of dementia almost 2.5 times, compared to people with none.
Meanwhile, developing two or more conditions between the ages of 60 and 65 was associated with a 1.5-fold higher risk.
For those with three or more chronic conditions at the age of 55, there was about a five-fold higher risk of dementia.
The risk fell dramatically if people were aged 70 before they developed chronic health conditions.
“Given the lack of effective treatment for dementia and its personal and societal implications, finding targets for prevention of dementia is imperative," said the experts, including researchers from University College London.
“These findings highlight the role of prevention and management of chronic diseases over the course of adulthood to mitigate adverse outcomes in old age.”
All those in the research were aged between 35 and 55 at the start of the Whitehall II Study (from 1985 to 1988).
“One in three people born today will go on to develop dementia in their lifetime," said Dr Rosa Sancho, head of research at Alzheimer’s Research UK.
“Age, genetics and lifestyle are all risk factors for developing the condition, but we know age is also a major risk factor for the development of other health conditions.
“Large, long-term studies like this are good for highlighting links, but we need research to explore the mechanisms between individual conditions.
“It is important to properly manage long-term health conditions and people who have concerns about any aspect of their health should speak to their GP.
“We do know that it’s never too early or too late in life to take action on brain health and there are things we can do to reduce our risk of dementia.
“This includes not smoking, drinking only in moderation, staying mentally and physically active, eating a balanced diet, and keeping cholesterol and blood pressure levels in check.”