www.lesswrong.com/posts/k8mwvvvpjMGcZLAKH/the-case-for-lifelogging-as-life-exten...

This sentence is misleading because it treats youthful or midlife health as something that raises Alzheimer’s risk. Major health authorities and longitudinal studies find the opposite: healthier cardiovascular and lifestyle profiles are associated with lower dementia risk later in life.

• WHO’s dementia risk-reduction guidance says people can reduce dementia risk by exercising, not smoking, avoiding harmful alcohol use, controlling weight, eating a healthy diet, and maintaining healthy blood pressure, cholesterol, and blood sugar.
• In the Whitehall II cohort study (25-year follow-up), ideal cardiovascular health at age 50 was associated with a lower incidence of dementia later in life.
• NHLBI’s summary of related research likewise states that good cardiovascular health reduced participants’ chances of developing dementia.

It is true that people who avoid other causes of death may survive to older ages where dementia becomes more common at the population level. But that is not the same as saying the healthiest young people have the highest chance of Alzheimer’s. On the individual-risk question, the evidence points the other way: better health lowers dementia risk.

This description overstates and misstates the hippocampus’s role in memory.

Authoritative neuroscience references describe the hippocampus as crucial for memory processing and consolidation—helping convert or stabilize new memories—rather than as the brain’s primary storage site for long-term memories.

• The NCBI StatPearls review on the hippocampus says it is involved in memory processing and that it helps convert short-term memory into long-term memory.
• An NCBI neuroscience text on long-term storage says the cerebral cortex is the major long-term repository for many aspects of memory, and that the hippocampus helps consolidate declarative information into cortical storage sites.

So the post’s wording is inaccurate: the hippocampus is essential for forming/consolidating many memories, but long-term memories are not primarily stored in the hippocampus itself.