Nicotinamide adenine dinucleotide (NADH) is an important cofactor, or "assistant," that helps enzymes in the work they do throughout the body. NADH particularly plays a role in the production of energy. It also participates in the production of L-dopa, which the body turns into the important neurotransmitter dopamine.

Based on these basic biochemical facts, NADH has been evaluated as a treatment for jet lag, Alzheimer's disease, Parkinson's disease, chronic fatigue syndrome, depression, and as a sports supplement. However, only the first of these uses has any meaningful scientific evidence behind it, and even that is highly preliminary.

Healthy bodies make all the NADH they need, using vitamin B3 (also known as niacin or nicotinamide) as a starting point. The highest concentration of NADH in animals is found in muscle tissues, which means that meat might be a good source—were it not that most of the NADH in meat is destroyed during processing, cooking, and digestion. In reality, we don't get much NADH from our food.