A large study of UK adults has found that having two or more chronic conditions (multimorbidity) in middle age is associated with an increased risk of dementia later in life, with this risk increasing in tandem with increased number of chronic conditions.
The study, published in the BMJ , by researchers from the Université de Paris and University College London set out to investigate whether multimorbidity at middle age – 55, 60, 65, and 70 – affects the risk of subsequent dementia in older age.
It is well-established that multimorbidity is common, particularly at older ages and in people living with dementia, and the authors highlighted how “multimorbidity is increasingly prevalent, starting in early adulthood and midlife”. They defined multimorbidity as the presence of at least two chronic conditions out of a predefined list of 13 chronic diseases that included hypertension, diabetes, coronary heart disease, COPD, and depression, but not dementia, and identified those with chronic conditions using data of over 10,000 British men and women from the Whitehall II Study. When participants joined this study in 1985-88 they were aged 35 to 55 and did not have dementia. The researchers identified subsequent cases of dementia using hospital and death records up to March 31, 2019.
The authors commented that: “Given the lack of effective treatment for dementia and its personal and societal implications, finding targets for prevention of dementia is imperative.”
Earlier Multimorbidity – Greater Dementia Risk
The researchers reported that of the 10,095 participants, 6.6% had multimorbidity at age 55 and 32% at age 70, with 639 cases of dementia being identified over a median follow-up period of 32 years.
They said that after taking account of factors such as age, sex, ethnicity, education, diet and lifestyle behaviours, multimorbidity at age 55 was associated with a 2.4-fold higher risk of dementia compared with people without any of the 13 chronic conditions, highlighting that “results showed that the risk is greater when these sorts of chronic conditions develop at a younger age (mid-50s) rather than later in life”.
They described how this association weakened progressively with older age at onset of multimorbidity and explained that at age 65, onset of multimorbidity before age 55 was associated with a 2.5-fold higher risk of dementia compared with a 1.5-fold higher risk in those with onset of multimorbidity between age 60 and 65. This meant, they said, “”or every 5 year younger age at onset of multimorbidity up to age 70, the risk of dementia was 18% higher”.
More Severe Multimorbidity – More Dementia Risk
Analysis of more severe multimorbidity – defined as three or more chronic conditions – showed further accentuation of the risk of dementia and younger age of onset of multimorbidity. The researchers said that “compared with people with no or one chronic condition, those with three or more chronic conditions at age 55 had a nearly fivefold higher risk of dementia”. They added that the risk was 1.7-fold higher when onset of multimorbidity was at age 70.
The authors pointed out that their study was observational and so can’t establish cause, and highlighted some limitations, namely possible misclassification of some dementia cases, and the fact that study participants are “likely to be healthier than the general population”.
However, the authors said that as it was a large study, with over 30 years of follow-up, and since results were similar after further analyses using death as the outcome measure, they had confidence in their findings.
They concluded by saying how their findings “highlight the role of prevention and management of chronic diseases over the course of adulthood to mitigate adverse outcomes in old age”.
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