Declining levels of NAD+ in cells is one of the proximate causes of loss of mitochondrial function with age. A number of approaches to increasing levels of NAD+ in cells involve using supplements that are derived from vitamin B3. Nicotinamide mononucleotide (NMN) is one of these, but has to date far less published human evidence for its effects than is the case for nicotinamide riboside (NR), making the small study noted here interesting. In general, the evidence for vitamin B3 derived compounds to increase NAD+ in older people is good, while the evidence for that increase to then produce benefits to health is mixed at best. For further consideration, regular exercise appears to be better at increasing NAD+ levels than this sort of supplementation, based on human trial data, and we have a fairly good idea as to the effect size of exercise when it comes to mortality and risk of age-related disease.
A small clinical trial of postmenopausal women with prediabetes shows that the compound NMN (nicotinamide mononucleotide) improved the ability of insulin to increase glucose uptake in skeletal muscle, which often is abnormal in people with obesity, prediabetes or Type 2 diabetes. NMN also improved expression of genes that are involved in muscle structure and remodeling. However, the treatment did not lower blood glucose or blood pressure, improve blood lipid profile, increase insulin sensitivity in the liver, reduce fat in the liver or decrease circulating markers of inflammation as seen in mice.
Among the women in the study, 13 received 250 mg of NMN orally every day for 10 weeks, and 12 were given an inactive placebo every day over the same period. "Although our study shows a beneficial effect of NMN in skeletal muscle, it is premature to make any clinical recommendations based on the results from our study. Normally, when a treatment improves insulin sensitivity in skeletal muscle, as is observed with weight loss or some diabetes medications, there also are related improvements in other markers of metabolic health, which we did not detect in our study participants."
The remarkable beneficial effects of NMN in rodents have led several companies in Japan, China and in the U.S. to market the compound as a dietary supplement or a neutraceutical. The U.S. Food and Drug Administration is not authorized to review dietary supplement products for safety and effectiveness before they are marketed, and many people in the U.S. and around the world now take NMN despite the lack of evidence to show clinical benefits in people.