Lifespan: Why We Age—and Why We Don't Have To review

Lifespan opens with a bold claim: aging is not an inevitable feature of biology but a disease — one that can be treated, slowed, and possibly reversed. David Sinclair, a Harvard geneticist who has spent three decades studying why organisms age, builds his argument around what he calls the Information Theory of Aging. Cells contain two kinds of information: digital (the DNA sequence, which stays largely stable across a lifetime) and analog (the epigenome, the chemical layer that tells genes when and where to switch on). Sinclair argues that aging is primarily a loss of epigenetic information — a degradation in the cell's ability to read its own instructions correctly — rather than the accumulation of genetic mutations most people assume it to be.

The book's scientific core traces a set of proteins called sirtuins, which Sinclair helped discover in yeast in the 1990s. Sirtuins act as a kind of cellular maintenance crew, repairing DNA damage and resetting epigenetic marks. Their activity depends heavily on NAD+, a molecule that declines with age. From here, Sinclair walks through the interventions that appear to activate these pathways: caloric restriction and intermittent fasting (both trigger a cellular stress response that ramps up sirtuin activity), exercise, cold exposure, and compounds like resveratrol, metformin, and NMN — molecules Sinclair takes himself and discusses with notable candor. He is careful to distinguish between what the animal data supports and what is proven in humans, though critics argue he sometimes blurs that line.