What Is The Difference Between NAD⁺ And NADH?

NADH is the reduced form of NAD⁺. They are two forms of the same coenzyme. In regards to supplementation, nicotinamide riboside (NR) is widely studied in both preclinical and clinical models. There is a large body of evidence that shows NR is transported directly into cells and NR safely and effectively increases NAD⁺ levels. In contrast, NADH is not well-studied and there have been no studies conducted comparing NR and NADH. Therefore, NADH’s bioavailability remains unknown. NADH is also significantly larger than NR, as it contains two large phosphate groups. The size and presence of the phosphate groups makes it difficult for NADH to enter cells. This may indicate that similarly to NAD⁺, NADH must be broken down into smaller components before it can enter cells and be used.