Longevity Briefs: It’s Never Too Late To Reduce Dementia Risk

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.

The problem:

As the global population ages, more and more people are living with dementia. The collection of diseases that make up dementia is currently incurable – that’s the bad news. The good news is that, according to estimates, nearly half of all dementia cases are preventable if you follow a healthy lifestyle (see below). But how late in life does this apply? Will switching to a healthier lifestyle in your 60s or 70s reduce your dementia risk in a meaningful way, or is it too late? Fortunately when it comes to dementia and age-related diseases in general, the evidence tends to point towards the former, and this study is no exception. Here, researchers in China followed older participants for a decade to see if changes in lifestyle behaviours at this age correlated with reduced dementia risk.

The discovery:

The study (which is still in preprint and has not yet been peer-reviewed) looked at data from 6,765 adults with a mean (average) age of 80.8 who participated in the China Longitudinal Healthy Longevity Survey, in which participants were followed for 10 years. Participants had normal cognitive function when they joined the study. Researchers then looked at five lifestyle behaviours: diet quality, sleep quality, physical activity, cognitive activity, and social engagement at the start of the study, 3 years later and 6 years later. These behaviours were assessed and scored using self-reported data. Cognitive function was then measured at two timepoints during the final 4 years of the study using the Mini-Mental State Examination (MMSE), a widely used 30-point questionnaire that assesses 5 aspects of cognitive function.

Rather than analysing each behaviour separately, the researchers used a statistical method that simultaneously models how multiple behaviours change together over time and categorises people into groups that follow similar overall patterns of behaviour. Three broad groups were identified. Some people began the study disengaged with healthy lifestyle behaviours, and their behaviours worsened over time – they were dubbed the ‘Low-Declining’ group, and made up the majority of participants at around 64%. Others began the study with moderate engagement, but their engagement increased over time (the ‘Moderate-Improving’ group). The smallest group was the ‘High-Declining’ group which, as you can probably guess, were highly engaged in positive lifestyle behaviours but whose engagement declined over time.

The study found that the Moderate-Improving group had a 63.2% lower risk of cognitive impairment compared to the Low-Declining group – not entirely surprising considering that Moderate-Improving participants were both healthier at the start of the study and also increased their engagement in healthy lifestyles practices during the study. The High-Declining group, on the other hand, had a 37.1% lower risk compared to Low-Declining, meaning they were more at risk of cognitive impairment than those in the Moderate-Improving group. The Moderate-Improving group also showed the slowest rate of cognitive decline between the three groups.

The implications:

One way of interpreting these results is that the trajectory of change in lifestyle is more important for preserving cognitive health than whether you were previously healthy. Modest, progressive improvements made from a modest starting point was associated with better protection than starting off healthy but slipping in later life.

However, since this study was observational in nature, it can only show correlation and not causation, which raises some important caveats. It is expected that people will become less engaged in healthy behaviours as they age, since they are unable to do as much due to normal age-related physical and cognitive decline. If someone starts to engage less with cognitively demanding activities for example, it could be be because they are already starting to experience cognitive decline due to accelerated cognitive ageing or underlying disease rather than the other way around. This is particularly relevant to the ‘High-Declining’ group – why would someone who was clearly motivated to maintain a healthy lifestyle in the past slip in older age? In some cases, it may be due to other factors beyond their control, with those factors being the actual reason for the cognitive decline.

Intervention studies in which participants are assigned healthy lifestyle interventions and followed up over time will be required in order to prove how much of this association actually comes from improving lifestyle in later-life. However, existing evidence for both cognitive decline and other aspects of ageing is cause for optimism. The take-home message is that you should try to be as healthy as possible throughout life, but that it’s never too late to start.