How are rates of dementia changing?

Before delving into the numbers, it is important to understand what the statistics mean. The word ‘prevalence’ describes the total number of people with dementia in a given population – be that individual countries or the global total. The term ‘incidence’ refers to the frequency of new dementia cases – ie the number of new cases of dementia developing each year.

A study published in 2020 found that between 1988 and 2015 the incidence rate of dementia fell by 13% each decade. So, the number of new people developing dementia was 13% lower each decade than the last. This decrease was mostly seen in men and correlated with lower smoking rates in men as well as fewer people developing heart disease and stroke. The researchers also suggested the results could be due to the current older generation having better access to education and healthcare than those before them. With each generation being so different, studies like this can only provide a snapshot of a population, rather than trends.

Although this result seems promising, it only applies to people in Europe and North America – both economically developed regions of the world with high life expectancies. A piece of research from 2020 that studied the whole world found that the global prevalence of dementia increased by 117% over largely the same time period. These researchers concluded that the increased size of the global population and the rising age of those within it were the cause of the total number of people with dementia more than doubling.

© 2021 The Author(s). Published by Elsevier Ltd.A graph showing the increase in the number of people with dementia from 1990 to 2050.

Then, in 2022, The Lancet published an updated estimation of the prevalence of dementia and predictions up to 2050. The review extensively explored changing rates of dementia in different age groups and across different countries all over the world. The researchers established that the number of global dementia cases will increase by 166% to 152.8 million people with dementia in 2050, mostly due to the growth and ageing of the world’s population.

Within this, the study found varying rates in different parts of the world, predicting the largest increase in dementia cases of 367% in North Africa and the Middle East, closely followed by what the researchers call eastern sub-Saharan Africa at 357%. This prediction is due to the booming population in these areas – so although proportionally the rate may not change dramatically, more people in total will develop dementia there.

By contrast, high-income areas of the Asia-Pacific region – such as Japan, Singapore, South Korea and Brunei – are predicted to see the smallest increase in dementia cases, with a percentage change of just 53%. The reason for this is likely due to the increased age of the populations in those places, which is somewhat counteracted by the expected decline in risk factors for dementia.

The map below (taken from the 2022 Lancet study) gives an indication of the percentage change in dementia cases per country, with dark blue indicating the smallest increase and dark red signifying the largest rates of increase.

© 2021 The Author(s). Published by Elsevier Ltd.A map - from the 2022 Lancet study on the prevalence of dementia - showing the predicted percentage change in dementia cases per country.

All studies mentioned found a higher prevalence of dementia in females than in males, partially due to the higher life expectancy of women, but potentially also due to underlying biological mechanisms of Alzheimer’s disease, the leading cause of dementia. Intriguingly, a review that differentiated between dementia subtype found that the prevalence of vascular dementia was greater in males than females.

In all genders, age is the biggest risk factor for dementia, with the prevalence of dementia doubling roughly every five years until age 85. But despite the global increase in the prevalence of dementia, the prevalence of the condition within each age group is estimated to remain constant.

Age and genetics are two factors that increase a person’s likelihood of developing dementia which can’t be avoided. However, there are several potentially modifiable lifestyle factors that increase dementia risk, outlined in 2020 in a review published in The Lancet. They offer a promising opportunity to tackle rising dementia rates, with the authors stating that ‘up to 40% of dementia prevalence might be preventable through interventions targeting modifiable risk factors’.

The list includes individual lifestyle factors such as alcohol intake, smoking and lack of exercise, which require motivational public health messaging to encourage individuals to combat them. Other factors are the responsibility of national and local governments to address, such as low education levels and air pollution. Medical conditions including high blood pressure, obesity, depression and hearing loss all increase a person’s risk of developing dementia, so improved prevention and treatment of these conditions will also help lower people’s risk of dementia.

Overall, it is important to understand the meaning behind shocking statistics about increased cases of dementia and consider the factors contributing to this and which of these may be attenuated.