Longevity Briefs: Dementia Risk Has Decreased. Why?

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:

The proportion of people around the World who are living with dementia is increasing. This is because the proportion of the population who are elderly (and therefore most at risk) is increasing, but that doesn’t mean that a given person, at a given age, is any more likely to have dementia now compared to if they had been born decades earlier. In fact, the risk of dementia at a given age seems to have decreased from generation to generation. That’s good news, as it confirms that factors besides the genes we inherit can bring the risk of dementia down. The question is: what are these factors, and how can we leverage them to keep lowering dementia risk until there is, one day, a way to cure it?

In this study, researchers examined data spanning two continents and several decades to investigate how dementia risk has changed and potentially uncover the main driving forces behind these changes.

The discovery:

Researchers examined data from birth cohorts in the US, Europe, and England specifically. This data included people who were born between 1890 and 1948. The study included in total about 150,000 participants aged 71 or older when the data was collected. Rather than using actual dementia diagnoses, researchers used a machine learning algorithm to identify individuals with probable dementia at a given time, based on factors like cognitive score and demographic characteristics. They chose to do this rather than use real dementia diagnoses partly because it would allow larger datasets to be analysed, and partly because dementia diagnosis practices vary across different countries and over time, which would have made comparisons difficult. They also tried to adjust for period effects (for example, the influence of GDP growth on the health of successive generations).

They found that, after accounting for age and period effects, individuals from more recent birth cohorts had significantly lower age-specific dementia prevalence rates in all three regions. For example, in the US, about 15% of people who were born between 1939 and 1943 had dementia in their early 80s, while that figure was 20% for those born two decades earlier. This decreasing trend was also found to be more pronounced in women than men.

The implications:

This study suggests a potentially encouraging trend: the risk of developing dementia may be decreasing across generations. This seemed to be driven, in large part, by decreased risk in women, which is probably related to improvements in education. We know that better educational status is strongly associated with reduced risk of cognitive decline and dementia. As women’s education has mostly caught up with men in the developed world, we might expect the trend of dementia risk reduction to fade. However, there have also been long term improvements in other environmental risk factors for dementia, such as less pollution, improved food quality and lower rates of smoking.

If this trend continues, we will still need to worry (a lot) about increasing dementia prevalence due to the ageing population, but at least it will be the only thing we need to worry about – dementia numbers shouldn’t increase beyond what would be expected from population ageing. This data also highlights how we still, as individuals, can have a lot of influence over whether or when we get dementia.