What's actually preventing cognitive decline, and when does the work need to start?

What are the major dementia categories?

Dementia isn't one disease. It's a category of conditions with different mechanisms:

• Alzheimer's disease. The most common form, accounting for roughly 60-80% of dementia cases. Characterized by amyloid plaques (protein buildups in the brain) and tau tangles (abnormal protein structures inside neurons). Strongly associated with insulin resistance, cardiovascular risk factors, ApoE4 genotype, and chronic inflammation
• Vascular dementia. The second most common form, driven by cerebrovascular disease and small vessel changes in the brain. Substantially preventable through cardiovascular risk reduction
• Lewy body dementia. Associated with movement symptoms similar to Parkinson's disease
• Frontotemporal dementia. Affects personality, language, and behavior, often before memory
• Mixed dementia. Combinations of the above, common in older adults

The interventions that prevent each form overlap significantly because the underlying drivers (vascular health, metabolic health, inflammation, sleep) affect multiple disease processes at once.

What are the modifiable risk factors for dementia?

The 2024 Lancet Commission identified 14 modifiable risk factors associated with dementia, organized by life stage:

• Early life: lower education
• Midlife (ages 45-65): hearing loss, traumatic brain injury, hypertension, high LDL cholesterol, alcohol misuse, obesity, depression, physical inactivity, diabetes
• Late life (over 65): smoking, social isolation, air pollution, vision loss

Addressing these factors at the appropriate life stage is associated with reduced dementia risk. The Lancet Commission concluded that doing so could prevent or delay roughly 45% of cases worldwide [Source: Lancet Commission 2024, Dementia prevention, intervention, and care].

Beyond the Lancet list, insulin resistance has emerged as a particularly strong modifiable risk factor. Brain insulin resistance contributes to amyloid accumulation, tau pathology, and neuroinflammation, leading some researchers to characterize Alzheimer's as "type 3 diabetes" [PMID: 39200352].

What does ApoE4 mean for individual risk?

ApoE genotype is the strongest known genetic risk factor for late-onset Alzheimer's disease [PMID: 38710950]. People inherit two copies of the gene, one from each parent, and the gene comes in three variants (ε2, ε3, ε4).

The risk pattern:

• One copy of ε4 (heterozygous): approximately 3 to 4-fold higher risk of late-onset Alzheimer's
• Two copies of ε4 (homozygous): approximately 9 to 15-fold higher risk, with an estimated 60% chance of developing Alzheimer's dementia by age 85
• The ε2 variant is associated with reduced risk

Roughly 25% of the population carries at least one ε4 copy. About 2% are homozygous for ε4.

Having ApoE4 doesn't determine outcome. Many carriers reach old age without developing Alzheimer's, particularly those who aggressively address modifiable factors. People with ApoE4 benefit disproportionately from optimizing metabolic health, cardiovascular markers, sleep, exercise, and inflammation. The genotype is information that changes how aggressively to apply preventive strategies, not a verdict.

What labs and assessments are useful for cognitive risk?

A useful cognitive risk assessment typically includes:

• Fasting insulin and HOMA-IR for early-stage insulin resistance
• hs-CRP (a general inflammation marker)
• Homocysteine (associated with cardiovascular and cognitive risk, often responsive to B vitamin optimization)
• Vitamin D, B12 with methylmalonic acid
• Omega-3 index (the proportion of EPA and DHA in red blood cell membranes)
• ApoB and Lp(a) for cerebrovascular risk
• Full thyroid panel, sex hormones
• ApoE genotyping as a one-time test
• Newer markers including p-tau and amyloid blood tests are becoming more available and may eventually become standard for cognitive risk assessment

What interventions actually protect cognition?

The interventions with the strongest evidence:

• Resistance training and aerobic exercise. The most consistently supported intervention across study designs
• Optimizing metabolic health. Addressing insulin resistance, maintaining stable blood sugar
• Cardiovascular risk reduction. Managing blood pressure, ApoB, Lp(a), and cholesterol where elevated
• Treating sleep apnea
• Treating hearing loss. Notably, hearing loss treatment substantially reduces dementia risk in people with hearing impairment
• Maintaining strong social connections and cognitive engagement
• Mediterranean-style or MIND-pattern eating
• Addressing nutrient deficiencies, particularly B12, vitamin D, omega-3, and folate
• Managing chronic inflammation
• Treating hypertension to target ranges
• Avoiding head trauma when possible

A multifactorial approach (addressing all contributing factors simultaneously) tends to produce better results than any single intervention, particularly in people with established mild cognitive impairment or early Alzheimer's. Several clinical protocols using this framework have shown promising results.

Are the new Alzheimer's medications worth knowing about?

The anti-amyloid antibody medications (lecanemab, donanemab) entered clinical practice recently as the first disease-modifying treatments approved for Alzheimer's. They show modest efficacy in selected patients with early-stage disease, but they carry meaningful side effect profiles, including risk of brain swelling and bleeding.

These medications represent a real advance, but they don't replace the importance of addressing modifiable risk factors. Prevention remains substantially more effective than treatment, particularly because the medications work in early-stage disease and don't help advanced cases.

The deeper picture

The window for cognitive prevention is decades long but only useful if it's used. A comprehensive cognitive risk assessment in your 40s or 50s, with appropriate biomarkers, ApoE genotyping, and modifiable risk factor optimization, is one of the higher-leverage things a person can do for long-term outcomes. Extend takes cognitive prevention seriously as part of comprehensive precision medicine care.