Middle-aged people with two or more chronic conditions are at increased risk of developing dementia later in life, according to research published in the BMJ.

The findings suggest that those who develop chronic conditions - such as high blood pressure, diabetes, coronary heart disease, depression, and chronic lung disease - at a younger age (mid-50s) are at greater risk compared to those who develop them later in life.

The study's authors say that given the lack of "effective treatment for dementia and its personal and societal implications", the results highlight that "finding targets for prevention of dementia is imperative."

Multimorbidity at age 55 was associated with a 2.4-fold higher risk of dementia

While multimorbidity is common, particularly among the older population, studies examining whether having multiple chronic conditions affects the risk of subsequent dementia are lacking.

The researchers therefore set out to fill this gap in the research by examining the long-term association between multimorbidity at ages 55, 60, 65, and 70 and subsequent dementia.

To do this, they drew on data collected from more than 10,000 British men and women in the Whitehall II Study. When participants joined the study between 1985 and 1988, they were aged 35 to 55 and free of dementia.

Of the 10,095 participants, 6.6% had multimorbidity at age 55 and 32% at age 70. Over a median follow-up period of 32 years, 639 cases of dementia were identified.

After taking account of a range of factors, multimorbidity at age 55 was associated with a 2.4-fold higher risk of dementia compared with people without any of the listed 13 chronic conditions; this association weakened progressively with older age at onset of multimorbidity. 

Participants who had severe multimorbidity (classed as three or more conditions), the importance of younger age of onset of multimorbidity for the risk of dementia was further accentuated. 

Findings highlight the role of prevention and management to mitigate adverse outcomes in old age

While the study is observational and cannot establish a cause, the researchers highlight this was a large study with over 30 years of follow-up.

They also found that the results were similar after further analyses using death as the outcome measure, which they say increases confidence in their findings on dementia.

For this reason, they say the findings "highlight the role of prevention and management of chronic diseases over the course of adulthood to mitigate adverse outcomes in old age."