More than 55 million people worldwide live with some form of dementia or cognitive impairment. In the next three decades that number is predicted to triple — climbing to 152 million people by 2050.
Dementia is often presented as an inevitable threat which looms in the distance of old age. Its causes are baked in with genetic risks and the advancing state of human ageing — or so the thinking goes.
But scientists are discovering that dementia is not set in stone. A large-scale reevaluation of the science, published by the Lancet journal, concluded that many more cases of dementia could be avoided than previously believed.
About 45% of the risk of developing dementia is due to 14 health factors. The Lancet Commission report, compiled by 27 leading dementia experts, is an update of a previous list of risk factors. The 2024 list included two new risks: high cholesterol and vision loss.
"This is important as, by understanding and acting on true risk factors of dementia, we can indeed delay, or prevent some cases of dementia," said Sarah-Naomi James, an expert in ageing diseases at University College London in the UK. James was not involved in writing the Lancet report.
What causes dementia?
Dementia is a group of many diseases, but the most common form is Alzheimer's disease.
It is caused by damaged nerve cells in the brain and leads to confusion and memory loss. People with dementia often cannot control their emotions, and their personalities may change.
Around half of the risk factors for dementia are due genetic mutations, which we inherit from our parents and grandparents.
But 45% of our dementia risk is due to 14 environmental risk factors and can therefore be reduced, the Lancet commission on dementia said.
The two new risk factors are associated with 9% of all dementia cases: 7% of cases are attributable to "bad" cholesterol from the age of 40 years, and 2% of cases are attributable to untreated vision loss in later life.
Other risk factor are: lower levels of education, hearing impairment, high blood pressure, smoking, obesity, depression, physical inactivity, diabetes, excessive alcohol consumption, traumatic brain injury, air pollution and social isolation.
Together, they make 40% of dementia risk.
Dementia prevention
The study authors call on national and international government bodies to be ambitious about dementia prevention.
"Actions to decrease dementia risk should begin early and continue throughout life," the authors wrote.
Currently, two-thirds of people with dementia live in developing countries. People in China, India and Sub-Saharan Africa are likely to be worst hit as the global population ages.
The authors wrote that there was "more potential for reduction in risk in low income and middle-income countries and among minoritized and lower socioeconomic groups."
In particular, reducing pollution levels and increasing educational standards in children and promoting midlife cognitive activity could have a significant impact on reducing dementia risks.
How to reduce your risk of getting dementia
The report offers guidelines for governments and health authorities to reduce dementia risk across people's lifespans, including:
making hearing aids accessible for those with hearing loss
ensuring good-quality education for all
supporting people to give up cigarettes
encouraging exercise and sport
encouraging use of helmets and head protection in contact sports and on bicycles
reducing high blood pressure from the age of 40
treating high cholesterol from mid-life
maintaining a healthy weight and treat obesity as early as possible
reducing high alcohol consumption
making sure people are not socially isolated or lonely, especially in old age
screening for eyesight problems and giving glasses to those who need them
reducing people's exposure to air pollution
"If we did simple things well, such as screening for some of the factors identified in this report, with adequate resources to perform this, we have the potential to prevent dementia on a national scale," said Masud Husain, a neurologist at University of Oxford in the UK. Husain was not involved in the report.
"This would be far more cost effective than developing high-tech treatments which so far have been disappointing in their impacts on people with established dementia," said Husain in a statement.
Is there a cure for dementia?
Researchers have been looking for medical treatments for dementia for decades, but their successes have been limited.
New hope arose after the discovery of a medicine called lecanemab, which slows the development of some forms of dementia, such as Alzheimer's in its early stages.
But the drug has proved controversial. Lecanemab was approved for use by the US Food and Drug Administration (FDA) in 2023, but the European Medicines Agency (EMA) rejected the drug for use in the European market in July 2024. The EMA reasoned the benefits of lecanemab did not outweigh the risks of a patient having serious side effects.
Scientists are still working to understand the disease's underlying biology. Without better understanding how dementia damages the brain, it's difficult to create new treatments to halt or reverse cognitive decline.
James highlighted that scientists still had major gaps in understanding how the 14 dementia risk factors highlighted by the Lancet were linked with dementia-related changes in the brain.
"We don't know how these factors (such as blood pressure) are affecting dementia risk, and which aspects of dementia pathology, type and development are conferring this risk," James said, adding that the report's recommendations ought to be encouraged by anyone interested in encouraging people to live healthier lives overall.