Cognitive decline is not an inevitable part of getting older. Genetics matter, but the Lancet Commission on Dementia Prevention has estimated that up to forty percent of dementia cases may be attributable to modifiable risk factors. That is a large share, and it is the share worth working on.
The goal is to protect executive function, processing speed, memory, and verbal fluency decades before any impairment appears, which means starting in your forties and fifties rather than waiting for a problem to name itself.
Decline is rarely one disease
Neurodegenerative disease is usually the convergence of several problems: cardiometabolic dysfunction such as insulin resistance, hypertension, and elevated ApoB, chronic neuroinflammation, mitochondrial dysfunction, reduced cerebral blood flow, sleep disordered breathing, micronutrient insufficiency, physical inactivity, and prolonged stress or isolation.
Alzheimer's disease and vascular dementia share overlapping cardiometabolic and inflammatory pathways, which is the reason prevention work starts upstream. The brain is a vascular organ. What protects your arteries protects your cognition.
The numbers we aim at
ApoB under 80 mg/dL, and often under 60 for higher risk patients. HbA1c under 5.3 to 5.4 percent. Fasting insulin under 5 micro international units per mL. HOMA-IR under 1.0. Systolic blood pressure around 115 to 120. A triglyceride to HDL ratio under 1.5.
These are not arbitrary. The SPRINT-MIND trial showed that intensive blood pressure control reduced the risk of mild cognitive impairment. Insulin resistance has been discussed in the literature in relation to Alzheimer's pathology because of impaired cerebral glucose metabolism, which is where the informal label type 3 diabetes comes from.
Exercise is the most reliable lever
Zone 2 aerobic work, roughly 150 to 200 minutes a week at sixty to seventy percent of maximum heart rate, improves insulin sensitivity, fat oxidation, and cerebral perfusion. Higher intensity intervals, one or two sessions a week of four by four minutes at ninety to ninety five percent, are a strong stimulus for brain derived neurotrophic factor.
Higher cardiorespiratory fitness is associated with lower dementia risk and greater hippocampal volume. Resistance training adds to it through IGF-1 signaling, glucose disposal, and the functional independence that keeps you active in the first place.
Sleep, and the reason apnea gets screened
Sleep is when glymphatic clearance removes beta amyloid, memory consolidates, and neuroinflammation is modulated. Untreated obstructive sleep apnea raises the risk of cognitive impairment and is associated with structural brain changes, which is why it gets screened for rather than assumed absent. Sleep fragmentation, short REM, and poor sleep efficiency all get looked at alongside it.
Nutrients, inflammation, and food
The deficiencies that turn up most often are vitamin D, B12, folate, magnesium, and omega-3 fatty acids. Low vitamin D is associated with increased dementia risk, and elevated homocysteine, often from impaired methylation, correlates with cortical atrophy and vascular risk.
Where testing shows a gap, the interventions are specific: EPA and DHA for membrane fluidity, magnesium threonate for synaptic support, B vitamins for methylation, and vitamin D brought into the 40 to 60 ng/mL range. Where testing shows no gap, we do not supplement for the sake of it.
On food, the PREDIMED study showed that a Mediterranean pattern reduced cardiovascular events, which lowers dementia risk through vascular mechanisms. In practice that means polyphenol rich vegetables, olive oil, fatty fish, high fiber whole foods, and far less ultra processed intake.
Two things that get skipped
Cognitive reserve is real, and social isolation, chronic stress, and untreated depression erode it. Learning, social connection, and purposeful activity protect executive function in a way no supplement does.
And alcohol deserves a plain sentence. Excess consumption is directly neurotoxic and raises dementia risk. Chronic cannabis use may impair hippocampal dependent memory. Neither is a comfortable thing to read, and both belong in an honest brain health conversation.
How this runs in practice
Define the endpoint first, which for most people is holding executive function into their eighties. Then audit the systems: ApoB, Lp(a), fasting insulin, hs-CRP, micronutrient panels, hormones, and VO2 max. Then build the foundations, meaning aerobic and resistance programming, nutrition aimed at insulin resistance, sleep, and hormone therapy where it is indicated. Advanced additions such as omega-3s, curcumin, and NAD precursors come last, once the foundations are actually in place.
Cognitive decline is not random. It is the cumulative result of decades of cardiometabolic stress, inflammation, poor sleep, and insufficient physiologic reserve. The earlier you intervene, the more of it you keep.
