Cognitive decline and the modifiable risks
The 2024 Lancet Commission puts fourteen risk factors behind roughly 45% of dementia cases worldwide. Most of them are things you have heard of.
goodWell supported, with the usual caveats about effect size.Revised 19 Jun 2026
The commission's list is unglamorous: hearing, blood pressure, movement, company.Photograph: CDC / Unsplash
Definition
Cognitive decline covers everything from the ordinary slowing of processing speed that accompanies ageing to mild cognitive impairment and dementia. Only the last is a disease category; the first is a normal, gradual change that most people notice and few people need to worry about.
The headline finding
The Lancet standing Commission’s 2024 report identifies fourteen modifiable risk factors that together account for around 45% of dementia cases worldwide. The 2020 report listed twelve; vision loss and high LDL cholesterol were added in 2024.
The list, across the life course:
- Early life — less education.
- Midlife — hearing loss, high LDL cholesterol, depression, head injury, physical inactivity, diabetes, smoking, hypertension, obesity, excessive alcohol.
- Later life — social isolation, air pollution, vision loss.
How to read “45%”
Carefully. This is a population attributable fraction: an estimate of how many cases might not occur if these exposures were eliminated at population level. It is not a personal probability, and it assumes causality that is better established for some factors (hypertension, smoking) than others.
It also does not mean an individual who does everything right is safe. Age and genetics remain the largest risk factors, and neither is on the list because neither is modifiable.
The claim is that a large share of dementia is not inevitable. Not that any particular case was preventable.
What this implies
Very little that is novel, which is the point. The interventions are the ones already recommended for cardiovascular health, plus three that get less attention:
- Treat hearing loss. It is the largest single midlife factor in the commission’s model, and hearing aids are an unusually concrete intervention.
- Get vision checked and corrected. New to the 2024 list.
- Stay socially connected. Infrequent social contact is on the list; the causal direction is harder to establish here, but the association is robust.
Open questions
Reverse causation haunts several factors — early dementia can cause social withdrawal, depression and inactivity years before diagnosis, which inflates their apparent contribution. The commission addresses this, and it is the main reason the estimate is a range in practice rather than a precise 45%.