A 40-year longitudinal study of Swedish women found a powerful correlation between mid-life fitness and late-life cognitive function. Women who were categorized as "high fit" in their 40s experienced, on average, nine more years of good cognitive health in their 80s compared to their low-fit counterparts.

A study on identical twins revealed that the twin with greater leg strength had a larger brain and better cognitive function over a 10-year period. This suggests that lower-body resistance training is a uniquely potent and specific intervention for preserving brain mass and preventing Alzheimer's.

While PET scans show lower glucose uptake in Alzheimer's brains, this may not be due to insulin resistance ("type 3 diabetes"). Studies show these brains can absorb glucose normally when cognitively stimulated. This suggests the issue is a lack of demand from inactive brain regions, not a failed supply mechanism.

Repetitive mental exercises like crossword puzzles merely reinforce existing neural pathways. To maintain cognitive health and build new connections, one must engage in novel challenges like learning a new language or skill.

A long-term study found many nuns had brains full of Alzheimer's plaques post-mortem, yet displayed no cognitive decline in life. Their constant social responsibilities and interactions acted as a continuous mental challenge, building new neural pathways that bypassed the damaged areas.

Higher education builds "cognitive reserve" by increasing neural connections. This creates a higher physiological baseline, meaning it takes much longer for age-related brain cell loss to manifest as cognitive impairment, a benefit often overlooked in financial ROI debates.

The severity of clinical dementia is not solely determined by neurological damage. Social factors like relationships, environment, and family support—termed "psychosocial reserve"—can be as crucial as neuropathology, explaining why some individuals with significant brain damage remain cognitively intact while others decline rapidly.

Despite common belief, only about 3-5% of Alzheimer's cases are driven by inherited genetic mutations. The vast majority are linked to lifestyle factors like diet, exercise, and sleep, making it a largely preventable disease if proactive measures are taken early in life.

Amyloid beta, often demonized as a toxic waste product in Alzheimer's, is fundamentally an antimicrobial peptide that protects brain cells. The problem arises not from its existence, but from the brain's inability to clear it effectively during sleep, leading to harmful accumulation.