What's Actually Ageing Your Brain? The Science of Neurodegeneration Risk

And why up to 45% of dementia cases might be preventable.

Here's a thought: the brain changes that lead to Alzheimer's disease can begin 20 to 30 years before a single symptom appears. That means by the time someone forgets a name or loses their train of thought in their 70s, the biological story started back in their 40s, or earlier. That's the uncomfortable truth. But here's the hopeful flip side: the same research that reveals this timeline also shows us that up to 45% of dementia cases worldwide could be prevented or delayed by addressing factors within our control. If you have ever wondered what is the point of having a medical examination in your 30's or 40's here is a good reason, many of the data points, such as Blood Pressure, Blood Sugar, LDL Cholesterol and Homocysteine are modifiable risk factors for dementia in older age. You can improve these and increase not just your lifespan but your healthspan too.

Some risk factors are fixed. Knowing them doesn't mean resignation, it means knowing where to focus extra effort elsewhere.

Age: The single biggest risk factor. Your risk roughly doubles every five years after 65.
Genetics: Particularly the APOE4 gene variant, meaningfully elevates risk for late-onset Alzheimer's disease.
Sex: women carry a disproportionate lifetime burden, in large part due to longevity.
Family history of dementia in a first-degree relative increases your baseline risk.

The Lancet Commission's List: 14 Factors, One Lifetime

The 2024 Lancet Commission on Dementia, one of the most comprehensive and authoritative reviews in the field, identified 14 modifiable risk factors that, if addressed, could prevent nearly half of all dementia cases globally. Crucially, they organised these by life stage, because when a risk factor hits matters enormously.

Early Life: The Foundation Years

Low educational attainment is the one factor flagged for early life, and it's not about intelligence. It's about cognitive reserve. Education builds neural connections, increases synaptic density, and creates the brain equivalent of a financial safety net. The more you build early, the more you can afford to lose later without noticing the difference.

Midlife: Where the Biggest Leverage Lives

This is where things get interesting, and actionable. The midlife risk factors carry some of the heaviest weight in the model:

High blood pressure. Midlife hypertension is particularly damaging. The target? Systolic BP ≤130 mmHg. Vascular damage and white matter injury are the mechanisms.
Obesity. Not just metabolic; obesity is associated with direct amyloid deposition in the brain.
Hearing loss. This one surprises people. It carries the largest single population-attributable fraction of any modifiable risk factor, up to 8% of all dementia cases. The mechanisms include social withdrawal, increased cognitive load, and reduced environmental engagement. An untreated hearing aid is not a vanity issue, it's a brain health issue.
Traumatic brain injury (TBI). Cumulative head impacts, not just single events, matter here. This includes contact sports, falls, and road traffic accidents. And this is not just a risk for dementia, a study of 8,000 male prisoners in Scotland in 2025 found that more than 80 per cent had once suffered a severe head injury. In Canada, a study of almost 10,000 homeless people found that more than half had a head injury that predated them becoming homeless
Alcohol excess. Directly neurotoxic and a gateway to other risk factors including hypertension and TBI.
Smoking. Associated with global brain atrophy. Even passive smoking is a documented risk factor.
Type 2 diabetes. Confers approximately a 46% excess risk for Alzheimer's disease. Poorly controlled blood glucose (HbA1c ≥8%) is particularly harmful.
Depression. The relationship is bidirectional. Depression triggers neuroinflammation, activating astrocytes that promote amyloid aggregation and tau phosphorylation, two of the hallmark pathological processes in Alzheimer's disease.
Elevated LDL cholesterol (newly added in 2024). Operating through both atherosclerotic and potentially direct amyloidogenic pathways.

Late Life: The Factors We Often Dismiss as "Just Ageing"

Physical inactivity. Exercise drives Brain-Derived Neurotrophic Factor (BDNF), sustains cerebrovascular blood flow, and supports neuroplasticity. Sitting still is not neutral for the brain.
Social isolation. Not a soft concern. Loneliness increases allostatic load and dramatically reduces the cognitive stimulation the brain needs to stay resilient.
Air pollution. Ultrafine particulates cross the blood-brain barrier and trigger neuroinflammation. This is a structural, environmental injustice as much as an individual concern.
Untreated vision loss. Like hearing loss, unaddressed visual impairment drives withdrawal from the world, and from the cognitive stimulation that world provides.

Beyond the Lancet List: What Else the Research Flags

The 14-factor model is the gold standard for population-level guidance, but the clinical picture goes deeper:

Elevated homocysteine and low folate. Classified among the highest-confidence modifiable risk factors for Alzheimer's disease in a major 2024 umbrella review.
Sleep disorders and obstructive sleep apnoea. During sleep, the brain's glymphatic system clears amyloid. Disrupted sleep impairs that clearance, and hypoxia accelerates damage. There are many wearable devices that will help you monitor sleep
Chronic psychological stress. Associated with hippocampal atrophy and dysregulation of the HPA (stress-hormone) axis.
Oral microbiome dysbiosis. Porphyromonas gingivalis, a bacterium associated with gum disease, has been detected in Alzheimer's brain tissue. This is an active and compelling area of research.
Subclinical organ dysfunction. A 2024 Nature Reviews Neurology analysis highlights that quiet dysfunction in cardiovascular, renal, hepatic, and metabolic systems can independently accelerate neurodegeneration, even when these conditions haven't yet been formally diagnosed. A routine medical examination will reveal this.

The Takeaway: It's Never Too Early, Never Too Late

The life-course model of neurodegeneration risk is both sobering and empowering. It tells us that the brain doesn't suddenly "go wrong" in old age, it responds, over decades, to the cumulative inputs it receives.

That means the question is never just "what should I do at 70?" It's "what am I doing at 40, 50, and 60 that will either build my brain's resilience or quietly erode it?"

Get a regular medical examination, control your blood pressure. Treat your hearing loss. Move your body. Connect with people. Sleep properly. Don't smoke. Go easy on the alcohol. These aren't just general health platitudes, they are, according to the best evidence we have, the specific levers most likely to keep your brain functioning well for decades to come.

The brain is not a passive bystander in its own fate. Neither are you.

Dr Tim Trodd

Family Medicine, Functional Medicine, General Practice

MBBS (London)
DCH (London)
DRCOG (UK)
MRCGP (UK)
FHKAM (Family Medicine)

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Reference

Livingston, G., Huntley, J., Liu, K.Y., Costafreda, S.G., Selbaek, G., Alladi, S., Ames, D., Banerjee, S., Burns, A., Brayne, C., Fox, N.C., Ferri, C.P., Gitlin, L.N., Howard, R., Kales, H.C., Kivimaki, M., Larson, E.B., Nakasujja, N., Rockwood, K., Samus, Q., Shirai, K., Singh-Manoux, A., Schneider, L.S., Walsh, S., Yao, Y., Sommerlad, A. and Mukadam, N. (2024). 'Dementia prevention, intervention, and care: 2024 report of the Lancet standing Commission.' The Lancet, 404(10452), pp. 572 to 628. Available at: https://doi.org/10.1016/S0140-6736(24)01296-0.