Diabetes and dementia: Reasons to be worried or optimistic?

If you ask the public to vote on health concerns, dementia comes very high on the list of diseases they worry about most. This is no surprise given the devastating effect dementia can have on the lives of both the individuals and their loved ones. The economic implications for the care of people with dementia are also very worrying. With this in mind, multiple international research initiatives are trying to determine how best to predict who is most at risk of dementia in order to put in place better preventative measures.

Diabetes, of course, is one condition linked to greater dementia risk, although the magnitude of risk is not well established and may be changing over time. With this in mind, Davis and colleagues sought to determine the excess risk of dementia in their longitudinal follow-up of the Freemantle Diabetes Study in Australia (summarised alongside). Notably, dementia is not an easy outcome to capture fully in any country, as many people will die before it is ever known that they had the condition. Thus, research in this area is much more difficult than when looking at outcomes such as myocardial infarction, which invariably result in hospitalisation. That said, the authors were able to capture data from a combination of databases available to them in Western Australia, an approach shown to improve the pick-up of people with dementia and which, therefore, makes the results more likely to be valid. The authors were also careful to account for the competing risk of death, as people with diabetes tend to die younger than those without, and thus would have less time to develop dementia.

Overall, the findings suggest that people with type 2 diabetes have a modestly higher risk of dementia, developing it around 1.7 years earlier. However, as they also died earlier, they lived with dementia for roughly the same length of time as people without diabetes.

These results parallel other studies demonstrating higher dementia rates and greater cognitive decline in people with diabetes (Biessels et al, 2014; Lyall et al, 2017). Collectively, the studies suggest more work is needed in this area to determine how best to delay dementia in people with diabetes, as well as elucidating the mechanisms behind this higher risk.

Looking beyond diabetes, there is some good news, as dementia rates appear to be lower than predicted given rising life expectancy. Indeed, in a recent US study, the prevalence of dementia in cohorts of people with average ages around 75 years were lower in 2012 than in 2000 by around 25% (Langa et al, 2017). The authors speculate that improving education could be relevant to this trend but, of course, lowering of cardiovascular risk over time via a whole host of factors (less smoking, lower cholesterol levels, better primary and secondary preventative measures) are also likely to be critical. Indeed, more and more evidence implies a link between cardiovascular disease and dementia. It is therefore hoped that, by better addressing cardiovascular risk in our patients with diabetes via multifactorial risk factor management across lifestyle, lipid, blood pressure and glycaemia domains, we are also lowering their risk of cognitive decline and dementia.

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