What is the controversy with NAD+?

NAD+ (nicotinamide adenine dinucleotide) is a substance every cell in the body needs for energy production and repair processes. Multiple human studies show that NAD+ levels gradually decline with age, presumably due to a combination of reduced production and increased consumption. Many researchers view this declining level as a contributing factor in age-related deterioration.

Oral supplementation with NR (nicotinamide riboside) or NMN (nicotinamide mononucleotide) demonstrably raises NAD+ concentrations in the blood and tissues of humans. That is one of the more firmly established facts in this field. In animal models such as mice and worms, NAD+ replenishment repeatedly led to a longer healthy lifespan and fewer age-related diseases. But an animal result is not yet a human benefit, and that distinction is precisely the heart of the debate.

The central problem is that higher NAD+ levels in humans have so far not been reliably translated into measurable health gains. Whether supplementation actually improves fitness, cognition, or metabolism remains unclear. The available clinical studies are too small and too short to draw firm conclusions. The substance rises in the blood, but what that concretely delivers for a person's health has not yet been demonstrated.

There is also a serious safety signal. In both cell studies and mouse experiments, NMN was found to protect pancreatic cancer cells against multiple chemotherapy agents and to support tumour growth. NAM (nicotinamide) showed a similar but weaker effect. Whether this also applies to humans has not been proven, but caution is warranted: people with active cancer or an elevated risk would be wise to discuss NMN supplementation with their doctor first.

The fundamental biology of NAD+ turns out to be more complex than was long assumed. The gut microbiome processes NR and NMN in ways that can alter their availability and activity. Moreover, each cell contains multiple separate NAD+ pools in different compartments, such as the mitochondria and the nucleus, each of which is regulated independently. This makes it difficult to predict exactly what a supplement does in the human body and explains why animal results are hard to translate.

Finally, there is the issue of conflicts of interest. Several lead authors of influential NAD+ review articles have financial ties to companies that sell these supplements, through patents, advisory roles, or equity stakes. This applies to a portion of the studies that serve as the basis for enthusiastic conclusions about NMN and NR. That does not automatically make their science incorrect, but it is a factor to weigh. Short-term supplementation appears safe and well tolerated, but large, long-term safety studies in humans are still largely lacking.