Nicotinamide mononucleotide (NMN) is a direct precursor to NAD+. In mammals, NMN can be made from nicotinamide (another form of vitamin B3) or nicotinamide riboside. The conversion from nicotinamide involves the enzyme NAMPT.
Scientists are not certain how NMN gets into the cells. It may be transported directly or may require more cofactors—such as vitamins and antioxidants—to make the process work smoothly.
NMN occurs naturally in various foods. The highest amounts are found in edamame, broccoli, cucumber, and cabbage. Moderate amounts are present in avocado and tomato. Smaller amounts show up in raw beef, shrimp, cow milk, and human breast milk. Because of a the low levels of NMN in these foods, NMN supplements may be a more effective way to increase levels and a few NMN supplements are currently available.
Most studies on the safety of NMN have been done in rodents. Only one safety study of NMN done in people has been published. In this clinical trial, researchers found that a single dose of up to 500 mg of NMN didn’t cause any serious side effects. Several clinical trials of NMN in the United States and other countries are currently underway or recently completed.