Longevity

Longevity Briefs: Two Or More Chronic Conditions In Middle Age May Double Dementia Risk Three Decades Later

Posted on 4 February 2022

Longevity briefs provides a short summary of novel research in biology, medicine, or biotechnology that caught the attention of our researchers in Oxford, due to its potential to improve our health, wellbeing, and longevity.

Why is this research important: We know that people with dementia are more likely to be living with multiple chronic conditions at the same time (multimorbidity). Common chronic diseases include high blood pressure, diabetes and heart disease, all of which become more frequent with age. Does having multiple chronic conditions make dementia more likely to occur? If so, does the age of onset of chronic conditions influence the risk of dementia later down the line?

What did the researchers do: In this study published in the British Medical Journal, researchers took
10 095 participants between the ages of 35 and 55, and followed them up for a median of 31.7 years. These participants were part of the Whitehall II Study, which recruited men and women employed in the London offices of the British Civil Service at the time of recruitment in 1985. Researchers investigated whether there was an association between multimorbidity at ages 55, 60, 65, and 70 and subsequent occurrence of dementia.

Key takeaway(s) from this research: After controlling for sociodemographic and lifestyle factors, having 2 chronic conditions (excluding dementia) at age 55 was associated with a 2.4 fold increase in dementia risk compared with those not suffering from any chronic conditions. For people with three or more chronic conditions, the risk was around 5 times higher compared with those with 1 condition or fewer, though this number is based on only 84 with three or more conditions at age 55.

Hazard ratios according to number of chronic conditions across age groups. The hazard ratio represents a person’s risk of dementia relative to that of someone with 0 or 1 chronic condition.
Source

This association was stronger if multimorbidity began earlier in life: an appoximate 18% increase in risk for every 5 years below the age of 70. As an example, those with three or more chronic conditions at age 55 had a roughly fivefold higher risk of dementia compared with those with 1 or no chronic conditions, whereas those who developed 3+ conditions at age 70 only had a 1.7 fold increased risk.

The main strengths of this study are that it was large and followed participants for 30 years. However, as a study that simply observes the correlation between two factors, it isn’t possible to conclude that having more chronic conditions at a younger age caused dementia in later life. It’s still possible, for example, that people who develop multimorbidity earlier have unhealthier lifestyles and hence are more likely to develop dementia, even though researchers did try to control for such confounding factors. It’s also worth mentioning that participants were recruited from a specific group (people employed in the London offices of the British Civil Service in 1985) and may not be representative of the wider population.

Regardless of the nature of the association, adopting lifestyle practices that reduce the risk of chronic disease is likely to result in reduced risk of dementia, as these conditions share many of the same risk factors anyway. In future studies, it would be useful to know more about which specific chronic diseases have the strongest associations with subsequent dementia onset.


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References

Association between age at onset of multimorbidity and incidence of dementia: 30 year follow-up in Whitehall II prospective cohort study: https://doi.org/10.1136/bmj-2021-068005

Midlife chronic conditions linked to increased dementia risk later in life: https://www.bmj.com/company/newsroom/midlife-chronic-conditions-linked-to-increased-dementia-risk-later-in-life/

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