Brain Health and Cognitive Decline: Modifiable Risk Factors

Dementia is among the most feared diagnoses in medicine, and for many people it feels like an inevitable consequence of ageing or bad luck in the genetic lottery. The evidence tells a more hopeful story. Age and genetics matter, but a substantial share of dementia risk is linked to factors that can be changed, many of them the same factors that drive heart disease, diabetes and stroke. For practitioners, brain health is therefore not a separate specialty but an extension of the cardiovascular and metabolic care they already provide.

The modifiable risk factors

The Lancet Commission on dementia prevention, intervention and care, updated in 2024, identified 14 modifiable risk factors across the life course and estimated that together they account for nearly half of dementia cases worldwide.

The estimate is based on population attributable fractions, which assume causal relationships and should be interpreted with caution. But the consistency of the associations, and the biological plausibility of many of them, make a strong case for addressing these factors, especially as most also reduce the risk of other diseases.

How these factors affect the brain

• Vascular damage: hypertension, diabetes, smoking and high cholesterol damage small and large blood vessels, contributing to vascular dementia and interacting with Alzheimer disease pathology.
• Cognitive reserve: education, cognitively stimulating activity and social engagement build the brain’s capacity to tolerate damage before symptoms appear.
• Sensory deprivation: hearing and vision loss reduce stimulation and social engagement and may increase cognitive load.
• Inflammation and metabolic effects: obesity and diabetes are associated with inflammation and insulin resistance, which may affect the brain.
• Direct injury: head injury and heavy alcohol use damage brain tissue.
• Depression: may be both an early symptom and a risk factor.

What intervention trials show

Blood pressure

In the SPRINT MIND study, intensive blood pressure control reduced the risk of mild cognitive impairment compared with standard control, though the reduction in probable dementia did not reach statistical significance. Treating hypertension in midlife is one of the best supported ways to protect the brain.

Multidomain interventions

The Finnish FINGER trial randomised older adults at increased risk to a 2 year programme combining diet, exercise, cognitive training and vascular risk management. The intervention group showed better cognitive performance than controls. Similar programmes are being tested in many countries.

Hearing

The ACHIEVE trial found that a hearing intervention did not slow cognitive decline in the overall population studied, but did slow it by nearly half in a subgroup of older adults at higher risk. Hearing loss is common, undertreated and associated with isolation, so identifying and treating it is worthwhile on multiple grounds.

Diet

The MIND diet, combining elements of Mediterranean and DASH patterns with an emphasis on leafy greens and berries, was associated with slower cognitive decline in observational studies. In a randomised trial, however, the MIND diet did not produce significantly greater cognitive benefit than a control diet when both groups followed mild calorie restriction. A healthy dietary pattern remains reasonable for overall health, while its specific cognitive effect is uncertain.

Supplements

Trials of ginkgo biloba, omega 3 supplements and vitamin E in people without deficiency have generally not prevented dementia. B vitamins slowed brain atrophy in one trial in people with mild cognitive impairment and raised homocysteine, suggesting a possible benefit in a subgroup, but not a general preventive role.

Physical activity

Regular physical activity is consistently associated with lower dementia risk in observational studies and improves cognitive function in some trials, as well as protecting cardiovascular and metabolic health.

Sleep and the brain

Sleep appears to play a role in clearing metabolic waste from the brain, and poor sleep and sleep apnoea are associated with cognitive decline. Whether treating sleep problems prevents dementia is not yet established, but it is reasonable to address them for their broader benefits.

Reversible causes of cognitive symptoms

Before attributing cognitive symptoms to dementia, several treatable causes should be considered. This is one of the most important contributions any practitioner can make.

Anticholinergic medicines deserve special mention. Higher cumulative use has been associated with increased dementia risk in observational studies, and reviewing medicines for anticholinergic burden in older adults is a simple and valuable step.

A practical brain health plan

1. Control blood pressure, particularly from midlife.
2. Manage diabetes and cholesterol.
3. Stop smoking and limit alcohol.
4. Be physically active, including aerobic and strength activity.
5. Check hearing and vision, and use hearing aids or correction where needed.
6. Stay socially and cognitively engaged.
7. Treat depression and address sleep problems.
8. Protect the head in sport and cycling.
9. Eat a healthy dietary pattern.
10. Review medicines for anticholinergic burden.

An illustrative case

A 71 year old retired engineer is brought by his daughter because of forgetfulness and withdrawal. He has hypertension that is poorly controlled, type 2 diabetes treated with metformin for 10 years, has stopped socialising because he struggles to follow conversations, and takes an anticholinergic medicine for bladder symptoms and a sleeping tablet. His assessment reveals B12 deficiency, significant hearing loss and moderate depressive symptoms. His B12 is replaced, he is fitted with hearing aids, his anticholinergic medicine and sleeping tablet are reviewed and tapered by his doctor, his blood pressure treatment is optimised and his depression is treated. 6 months later his daughter reports that he is more engaged, more alert and back at his weekly club. A specialist memory assessment later finds mild impairment only, and he continues with a brain health plan.

A hopeful message

Dementia is not simply fate. Many of its risk factors are modifiable and overlap with those of heart disease and diabetes, and some cognitive symptoms have reversible causes. Practitioners who treat brain health as part of whole person care can make a meaningful difference, both to individual patients and to the wider burden of dementia.