Nutrition Facts with Dr. Greger

More on Boosting NAD+

September 18, 2025

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  • While NMN and NR are NAD precursors with some demonstrated benefits in rodents, human studies so far show limited efficacy and established safety for NMN is lacking. 
  • Direct NAD supplementation faces challenges with stability and bioavailability, making precursors like NMN and NR the focus of research. 
  • The efficacy and safety of various NAD-boosting supplements, including NMN, NR, and tryptophan, are still under investigation, with some showing potential risks and inconsistent results in human trials. 

Segments

NMN vs. NR Precursors
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(00:00:18)
  • Key Takeaway: NMN and NR are NAD precursors with differing proposed mechanisms of cellular entry and stability, but direct head-to-head comparisons in humans are limited.
  • Summary: This segment discusses NMN as a supplement to boost NAD production, comparing it to NR. It explores arguments for NMN’s potential advantages in stability and direct precursor status, as well as counterarguments regarding cell membrane permeability and the need for conversion to NR.
Human Studies on NMN
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(00:02:13)
  • Key Takeaway: Current human studies on NMN show minimal to no significant effects on various health markers in healthy individuals, and its efficacy in metabolically compromised individuals is also limited.
  • Summary: This section reviews the limited human studies on NMN, detailing findings from trials on healthy men, middle-aged men and women, and amateur runners, noting a lack of significant improvements in most measured variables. It also touches on a study in pre-diabetic women showing a modest improvement in muscle insulin sensitivity but no broader metabolic benefits.
NMN Safety and Concerns
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(00:05:23)
  • Key Takeaway: While NMN is found in some foods, supplemental doses are significantly higher, and its long-term safety for human consumption is not yet established, with theoretical concerns about nerve degeneration.
  • Summary: This part addresses the safety of NMN, contrasting its natural occurrence in foods with supplement doses. It highlights the lack of human safety evaluations for NMN, unlike NR, and discusses potential negative metabolic consequences and the theoretical risk of nerve degeneration based on animal and in vitro studies.
Other NAD Boosters
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(00:07:48)
  • Key Takeaway: Direct NAD supplementation is impractical due to instability, and other precursors like niacin and tryptophan have their own limitations and potential side effects, with tryptophan restriction showing promise in animal studies.
  • Summary: This segment shifts to other NAD-boosting strategies, discussing niacin and tryptophan. It explains why direct NAD intake is difficult, highlights the inefficiency and side effects of tryptophan, and mentions animal studies suggesting tryptophan restriction might be beneficial for longevity and cancer rates.