Alzheimer’s disease and other dementias were the leading cause of death in Britain in 2021 (followed by Covid-19 and heart disease), and a top 10 cause of death in the United States. Dementia is a general term used for several diseases that destroy nerve cells and damage the brain, leading to difficulty with memory, thinking and other cognitive functions. Behind those statistics is a heartbreaking condition for individuals (and their loved ones) as they become confused and disoriented, struggle to recognise family, friends and caregivers, and lose the ability to live independently.
Recent studies from across the world have highlighted that dementia cases are likely to rise dramatically. For instance, an analysis of 15,000 middle-aged US adults in Nature Medicine in January 2025 found that in study participants, the lifetime risk of developing dementia after 55 was 42%. Basically, an estimated 42% of over 55-year-old Americans will eventually develop dementia. This is considerably higher than previous studies had found. The authors say that the number of US adults who will develop dementia annually is expected to double over the next four decades. The numbers are eye-wateringly high, and they align with a growing concern in public health that with more people living longer and elderly people becoming a larger proportion of the population, cases will increase dramatically, with associated health and social care challenges.
However, these estimates of a future tsunami of dementia are now being challenged, given data showing that age-specific dementia rates declined by about two-thirds among US adults between 1984 and 2024. Similar falling rates were found in Sweden, the Netherlands, the UK and France. To take it out of jargon, yes, the absolute number of people developing dementia is going up because of ageing and the increasing number of elderly people. Yet, at each age – whether it’s 50 or 60, or 70 – it seems that most studies show that the rate of developing dementia at a given age is going down, compared with what we’ve seen in the past. We’re getting better at living longer, with cognitive impairment still occurring but at a later age.
There’s no simple answer to explain the decrease in age-specific dementia rates, although there are several hypotheses, such as lower smoking rates, higher education, better treatment of high blood pressure and early detection of cognitive impairment. We know that there are modifiable factors – that is, things that individuals and communities can do to prevent the onset of dementia. The Lancet Commission on dementia prevention estimates that about 45% cases of dementia are preventable if 14 modifiable risk factors are addressed. These include education, hypertension, hearing loss, vision loss, smoking, obesity, depression, physical inactivity, diabetes, high LDL cholesterol, excessive alcohol consumption, air pollution and loneliness and traumatic brain injury. The causes of dementia are complex, and include genetic predisposition, but there are also significant actions that we can each do to improve the health of our brain and delay the onset of disease.
Over the past couple of decades we’ve become better at understanding these risk factors and developing public health policies and education to address them. We’ve also seen massive scientific progress in medical drugs. For instance, the past couple years have seen the development of two new treatments for Alzheimer’s (donanemab and lecanemab), which clinical trials indicate slow down the progression of the disease – and which have led to bold claims, by pharmaceutical companies such as Lilley, that this is the “beginning of the end” of Alzheimer’s. Caution is needed, given the high cost of treatment and serious side-effects that these medicines can cause, but it still shows the slow and steady forward movement in dealing with the disease.
The decrease in age-specific dementia rates contrasts with cancer, where incidence is expected to keep going up in young people. Referred to as the “birth cohort effect”, the numbers show that each group of people born at a later time have a higher risk of developing cancer later in life. So someone born in 1990 is at a higher risk of developing cancer younger than someone born in 1980, who has a higher risk than someone born in 1970. For instance, colorectal cancer increased by 70% among those aged 15-39 in G20 countries between 1990 and 2019. We’re doing better in some areas of health like delaying dementia and losing ground in others such as cancer prevention.
Yes, we all have to die at some point, and something in our mind or body will eventually break down with time, but the public health goal is to push disease as far as possible into the future. We know that there are things we can do to delay dementia, and we are already seeing progress likely linked to public health policies and medical advances. Behind the headline news of a dementia tsunami, there’s some good news too.
Prof Devi Sridhar is chair of global public health at the University of Edinburgh, and the author of How Not to Die (Too Soon)
