Endogenous metabolism in endothelial and immune cells generates most of the tissue vitamin B3 (nicotinamide).

In mammals, nicotinamide (NAM) is the primary NAD precursor available in circulation, a signaling molecule, and a precursor for methyl-nicotinamide (M-NAM) synthesis. However, our knowledge about how the body regulates tissue NAM levels is still limited. Here we demonstrate that dietary vitamin B partially regulates plasma NAM and NAM-derived metabolites, but not their tissue levels.

Low NAD Levels Are Associated With a Decline of Spermatogenesis in Transgenic ANDY and Aging Mice.

Advanced paternal age has increasingly been recognized as a risk factor for male fertility and progeny health. While underlying causes are not well understood, aging is associated with a continuous decline of blood and tissue NAD levels, as well as a decline of testicular functions. The important basic question to what extent ageing-related NAD decline is functionally linked to decreased male fertility has been difficult to address due to the pleiotropic effects of aging, and the lack of a suitable animal model in which NAD levels can be lowered experimentally in chronologically young adult males.