Vitamin B3 Choices
NAD, NADH, Niacin, NMN, NR

Dec 2021: We find that, despite systematic claims of overall changes in NAD+ levels with aging, the evidence to support such claims is very limited and often restricted to a single tissue or cell type. This is particularly true in humans.

Dec 2021: Best way to deal with Alzheimers is to prevent it: vit B3. A diet with a relatively high amount of vitamin B3 from regular foods such as chicken, peanuts and tuna protects against Alzheimer's disease.

Vitamin B3/Niacin supplementation dramatically and beneficially raises growth hormone levels  for several hours.  Pilot Study-Effects of Niacin Administration on FFAs-Free Fatty Acid & Growth Hormone in Obese Children Pediatr Obesity 9-21-2016.

Science 9 July 2021 pg 172 - Faulty microbiome bacteria deplete nicotinamide (vitamin B3) which causes ALS (amylotropic muscular dystrophy). Deficiency also causes other dementias like Alzheimers and Parkinsons. This is clear evidence of the value of B3 supplementation.

From Philip Lee Miller, MD www.antiaging.com California Age Management Institute: I am happy to have started this thread.  I realize this is a very heated topic.  I submitted the article from Dr. Berkmayer. It is indisputable that most significant molar production of ATP is produced through oxidative phosphorylation - the ETC.  NADH is converted to NAD+ in complex 1.  It is well known that NAD+ does not cross mitochondrial membranes.  So all the NAD "precursors" such as NR and NMN as well as NAD+ do not penetrate the mitochondrial matrix. Intra-mitochondrial NAD and NADH must be produced de novo from salvage pathways.

From Roc Ordman, PhD: It has been reported in Science that NAD levels in humans decrease with age (ref). NAD is biosynthesized from vitamin B3 (niacin), which is safe when consumed up to 35 mg/day.  Over that level, the only hazard is flushing. Excess niacin is excreted.  I take 500mg/day with no ill effects. The RDA for adults is 16 mg/day of NEs for men and 14 mg/day of NEs for women. Recently, the median intake of preformed niacin from food in the United States was approximately 28 mg for men and 18 mg for women. So taking a niacin supplement is a safe, inexpensive and convenient way to maintain niacin levels. Other forms like NMN, NR, NADH, and NAD are likely to be a waste of money. Any study supporting their use should have a control using niacin instead. The edietary reference intake report of the National Library of Medicine describes metabolic transport and function of NAD, niacin, etc.

ADDITIONAL DISCUSSION WITH REFERENCES