NAD+, cell repair and cancer

NAD+ consumption during DNA repair

Repair has a cost. PARP enzymes consume NAD+ during the response to DNA damage, while sirtuins use it in regulating metabolism and stress responses. Ying’s review of NAD-dependent cellular functions brings energy metabolism, signaling and cell death into the same account.

Calling NAD+ “energy” leaves out the spending. Calling it “repair” leaves out the rest of the cell. I prefer the busier picture: several processes drawing on a resource whose supply and location matter. The review of NAD+ in metabolic disease explains how these activities connect changes in energy status with metabolic adaptation.

A protein consuming NAD+ during repair establishes a cellular mechanism. The benefit of adding a precursor still needs its own human evidence.

CD38 and the aging mouse

In the CD38 deletion experiment, mice lacking this NAD-consuming enzyme were protected against the age-related fall in NAD+ and had better mitochondrial function. It is an elegant way to test the role of consumption: change the machinery that spends NAD+ and observe what remains.

CD38 also shapes immune-cell signaling and metabolism, as described in the review of the CD38–NAD+ axis. The animal experiment therefore points into a network of functions, rather than supplying a simple instruction to raise a blood level.

The precision of that genetic experiment matters. Deleting an enzyme in a mouse is a very particular intervention, and that precision would disappear if the result became a general claim about human pills.

SLC25A47 and liver tumors in mice

The SLC25A47 study in mouse liver examined a mitochondrial NAD+ transporter. Its deletion increased liver lipid content and promoted tumorigenesis, the development of tumors. The study connected local NAD+ transport with SIRT3 and AMPKα, proteins involved in metabolic regulation.

This finding complicates any blanket claim that reducing NAD+ is protective. Here, disrupting transport worsened the outcome. It also gives no permission to reverse the experiment in imagination and promise that an oral precursor prevents human liver cancer.

For me, the location of the disruption is the most compelling feature. A whole-blood measurement cannot settle what is happening inside liver mitochondria. The review of NAD+ homeostasis in human health and disease describes several ways supply can become disturbed, including impaired production and increased consumption.

The concern about an existing cancer

NAD+ helps sustain cellular metabolism. That creates a theoretical concern that additional availability could support a cancer already present. The health-and-disease review describes biology whose consequences depend on context; the concern does not establish that NMN or NR caused cancer in a human trial.

Neither reassurance nor a cancer scare seems justified to me by that uncertainty. The useful next question is which tissue, which disease context and which outcome a study actually examines. Individual cancer care requires the treating clinician's assessment.

The 2025 synthesis of human NAD+ precursor evidence describes limited efficacy and sparse tissue-specific data. Those gaps leave the broad claims about longevity and disease prevention unresolved. The human trial comparison gives the results that can already be described more precisely.