Having two or more chronic conditions (known as multimorbidity) in middle age is associated with an increased risk of dementia later in life.
Common chronic conditions include high blood pressure, diabetes, coronary heart disease, depression, and chronic lung disease (COPD). The results show that the risk is greater when these sorts of chronic conditions develop at a younger age (mid-50s) rather than later in life.
Evidence shows that multimorbidity is common at older ages and in people living with dementia. However, it is a relatively unstudied area on whether multiple chronic conditions at earlier ages affect the risk of subsequent dementia. The researchers set out to examine the long-term association between multiple chronic conditions at ages 55, 60, 65 and 70 and subsequent dementia.
The study used British adults to analyse the link to dementia and was published by The BMJ.
Studying chronic conditions and dementia
Their findings are based on data collected from over 10,000 British men and women taking part in the Whitehall II Study, which looked at the association of social, behavioural, and biological factors on long-term health. When the participants joined the study in 1985-88, they were aged 35 to 55 and free of dementia.
For this study, multimorbidity was defined as the presence of at least two chronic conditions out of a predefined list of 13 chronic diseases, excluding dementia. Subsequent cases of dementia were identified using hospital and death records up to 31 March 2019.
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.
A range of factors was accounted for including age, sex, ethnicity, education, diet and lifestyle behaviours, and the researchers found that multimorbidity at age 55 was associated with a 2.4-fold higher risk of dementia (1.56 per 1,000 person-years) compared with people without any of the 13 chronic conditions.
The association weakened progressively with older age at the onset of multiple chronic diseases.
For example, at age 65, the onset of multimorbidity before age 55 was associated with a 2.5-fold higher risk of dementia (3.86 per 1,000 person-years) compared with a 1.5-fold higher risk (1.85 per 1,000 person-years) in those with the onset of multimorbidity between age 60 and 65. For every 5-year younger age at onset of multimorbidity up to age 70, the risk of dementia was 18% higher.
When the researchers examined more severe multimorbidity (defined as three or more chronic conditions), the importance of the younger age of onset of multiple chronic conditions for the risk of dementia was further accentuated.
For example, compared with people with no or one chronic condition, those with three or more chronic conditions at age 55 had a nearly five-fold higher risk of dementia, whereas the risk was 1.7-fold higher when the onset of multimorbidity was at age 70.
The study was observational; therefore, a cause cannot be established, and the researchers pointed out some limitations. This included possible misclassification of some dementia cases and the fact that study participants are likely to be healthier than the general population.
However, this was a large study with over 30 years of follow-up, and results were similar after further analysis using death as the outcome measure, which the researchers said increased confidence in their findings on dementia.
“Given the lack of effective treatment for dementia and its personal and societal implications, finding targets for prevention of dementia is imperative,” they wrote. “These findings highlight the role of prevention and management of chronic diseases throughout adulthood to mitigate adverse outcomes in old age.”