Harvard Doctor reveals #1 Cause of Aging You've Never Heard Of | Dr. Andrew Salzman

June 25, 2026

AI Summary

5 min read

Dr. Andrew Salzman, a Harvard-trained ICU physician, began his career studying septic shock in the 1990s. While working at Mass General, he attended a talk on the "leaky gut"—a concept that was then considered fringe. That talk sent him down a path that eventually led him to identify NAD as "the centerpiece of biology" and to reframe aging not as a process of wearing out, but as a failure of repair. In this conversation with Dr. Josh Axe, Salzman explains the cellular machinery that runs on NAD, why inflammation is the primary enemy of that machinery, and why creatine deserves attention far beyond the gym.

The Leaky Gut Origin Story

Salzman’s research began in the early 1990s when he was an ICU fellow at Mass General. He attended a talk by Dr. Mitchell Fink on the "leaky gut"—a concept that was then considered fringe. Salzman was electrified. He joined Fink’s lab and built a system to measure intestinal permeability. The key discovery: when gut cells were stressed, their ATP levels dropped, and the gut barrier became leaky. Later, a Japanese surgeon named Naoki Uno joined the group, and together they showed that inflammatory cytokines caused ATP to fall and the gut to leak.

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What you'll learn

1 (01:30) **Aging as a Defect in Repair, Not Wear-and-Tear** - Dr. Salzman introduces his core philosophy: aging is a failure of repair, not a wearing out like a machine.
2 (03:14) **Introduction & Dr. Salzman's Background** - Dr. Josh Axe introduces Dr. Andrew Salzman, a Harvard-trained ICU physician and pioneer in aging science.
3 (04:38) **The Origin Story: From Leaky Gut to PARP** - Dr. Salzman recounts his 1991 discovery of leaky gut and the link between cellular energy and gut barrier integrity.
4 (09:54) **The PARP-NAD-ATP Connection** - Reading a paper on PARP, he connected DNA damage, NAD consumption, and ATP failure, a key mechanism in critical illness.
5 (16:06) **How NAD and Creatine Power the Cell** - A detailed explanation of the cellular energy system: NAD is essential for making ATP in the mitochondria, but creatine is the distribution system.
6 (23:00) **Dietary Sources of NAD and Creatine** - Discussion on food sources for NAD precursors (vitamin B3) and the importance of gut health for nutrient absorption.
7 (26:17) **The Inflammation "Hole in the Bucket"** - Chronic inflammation is the primary driver of NAD depletion, creating a vicious cycle.

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Guests on this episode

Dr. Josh Axe

Show Notes

What if aging isn’t simply your body “wearing out”… but your body losing the ability to repair itself? In this episode, Dr. Andrew Salzman joins Dr. Josh Axe to explain why chronic inflammation, leaky gut, and depleted NAD may quietly drain the very energy your cells need to heal, think, move, and survive.

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00:00 — Why Aging Is A Defect In Repair, Not Wear And Tear

01:42 — Meet Dr. Andrew Salzman: Harvard ICU Doctor & NAD Pioneer

03:07 — The 1991 Discovery That Changed Leaky Gut Research

06:59 — Why Doctors Dismissed Leaky Gut For Years

09:46 — DNA Damage, PARP Activation & The NAD Collapse

12:41 — How PARP Inhibitors Stopped Leaky Gut In The Lab

14:35 — What NAD Actually Does Inside Your Cells

21:31 — Best Food Sources For NAD & Creatine Support

24:55 — How Chronic Inflammation Activates PARP

25:56 — CD38: The Enzyme Draining Your NAD With Age

27:10 — NR vs NMN vs Niacin: Which NAD Supplement Makes Sense?

30:02 — Why NAD Is The “Centerpiece Of Biology”

34:24 — The Mouse Study Linking CD38, NAD & Ovarian Aging

35:30 — Why The Brain Is So Vulnerable To Low Cellular Energy

36:57 — Mitochondri