Dr. Nir Barzilai: Inside the Geroscience Hypothesis — and Why He Takes Rejuvant

On Longevity Technology — Unlocked, Dr. Nir Barzilai — President of the Academy of Geroscience and Professor of Medicine at Albert Einstein College of Medicine — walks through the geroscience hypothesis: the idea that targeting the biology of aging itself can delay multiple diseases at once. The conversation covers the drugs already showing healthspan benefits today (SGLT2 inhibitors, metformin, GLP-1s), and what's coming next (mTOR, sirtuins, NAD+). Near the end of the episode, he turns to supplements — and to why, of the ones he's seen, he personally takes Rejuvant.

What Dr. Barzilai said

Excerpted from the interview (jump to this part on YouTube), lightly edited for readability.

I'm just going to pick one example and explain to you why I'm picking that: Rejuvant. Phil, are you taking Rejuvant? No? You think I should? So — maybe this is my premiere, my coming out of the closet for the first time — I'm taking Rejuvant.

Why did I decide to take it? Let me just say: supplements are great for the economy — billions of dollars — but multi-supplements are probably increasing your chance of mortality, even if you exercise and diet. Because we don't know anything — there's no clinical study on supplements, no combination trial of therapy and supplements. It's really risky, in my mind, compared to the FDA drugs I mentioned earlier.

But certainly there are supplements that are going to be beneficial, maybe on a personalized-medicine level, because they're doing something. The science behind Rejuvant comes out of Brian Kennedy's lab, and I like the idea of showing really good data in animals — without that I wouldn't believe anything. So they've shown an effect on health and longevity in animals. That's not enough, because it doesn't have the clinical studies. But they published something really interesting: when they asked people about their satisfaction across, I think, 76 different drugs, Rejuvant was the best or top three — I don't remember exactly which. For me, the idea that people subjectively notice a change is really important.

So I went to my doctor, we did before-and-after, and I decided to go on it — in combination with metformin, fasting and exercise. But it improved things — I feel it improved my ability to maintain concentration. And, maybe this is my bias, some of my hair that was whiter before became darker. I don't know if that's real or a bias, but that's what I'm doing, in the context of the rest of my health.

So that's as far as I can say, and it's not really about Rejuvant specifically — it's about picking whatever you want, as long as you can measure it and it actually improves your health.

The Aging Cell findings

Dr. Barzilai's guardedly positive read on Rejuvant echoes what he told the peer-reviewed journal Aging Cell after its 2026 study on 84 commonly used longevity supplements and drugs:

While many nutraceuticals have generated more enthusiasm than meaningful geroscience-based evidence, Rejuvant has at least a plausible mechanism of action and supportive preclinical data. In addition, post-marketing experience suggests a more reassuring profile for use, safety, and user satisfaction than the sweeping claims made for many other supplements. In today's longevity marketplace, that may not be a gold standard — but it is about as close as one gets to an adult in the room.

Read the full press release and the study itself.