The Brain's Immune System Is Under Your Control

Neurologist David Perlmutter has spent decades arguing that brain degeneration isn't inevitable. In his new book Brain Defenders, he consolidates a career's worth of evidence into a single, actionable framework: the health of your brain depends on the behavior of its resident immune cells, called microglia, and their behavior depends on your metabolism. "It is almost a fully preventable situation that people shouldn't fear," Perlmutter says of Alzheimer's disease. "People should feel empowerment."

That claim matters because the numbers are stark. Forty to fifty percent of Americans who live to age 85 will be diagnosed with Alzheimer's. Among people 65 and older, one in nine already has dementia. Yet Perlmutter insists these outcomes are not fixed. The shift from a healthy brain to a degenerating one is driven by mechanisms we can influence.

Microglia: The Brain's Firefighters and Arsonists

Microglia are the brain's innate immune cells. In their healthy state, Perlmutter calls them "brain defenders." They maintain synapses, support the blood-brain barrier, and keep neurons functioning. But when triggered, they transform into what he calls "the evil twin" — a destructive M1 configuration that destroys synapses, creates neuroinflammation, and degrades the blood-brain barrier.