What Is NAD+? A Guide to Nicotinamide Adenine Dinucleotide
If you have been researching longevity, cellular health or healthy ageing, you may have come across NAD+. But what is NAD+, and why has it become such an important area of scientific research?
NAD+ (nicotinamide adenine dinucleotide) is a naturally occurring coenzyme found in virtually every living cell. It plays a central role in cellular metabolism, helping cells convert nutrients into usable energy. NAD+ also acts as a substrate for enzymes involved in processes including DNA repair and cellular signalling, making NAD+ levels an increasingly studied area of ageing and metabolic research.
What Does NAD+ Do?
One of the most important functions of nicotinamide adenine dinucleotide is its involvement in energy metabolism. NAD+ accepts electrons and is converted into NADH; this NAD+/NADH cycle is essential to processes that ultimately support the production of ATP, the primary energy currency used by cells.
NAD+ is also required by several groups of enzymes, including sirtuins and PARPs, which are involved in cellular regulation and DNA repair. These multiple functions help explain why NAD+ research now extends across metabolism, mitochondrial function and the biology of ageing.
Does NAD+ Decline With Age?
The relationship between NAD+ and ageing is one of the most researched aspects of NAD biology. A human study analysing skin tissue from 49 people, ranging from newborns to 77 years old, found a significant negative correlation between tissue NAD+ levels and age in both males and females.
However, newer research shows that the picture is more complicated. A 2026 Nature Metabolism study examined seven independent human cohorts and found that whole-blood NAD+ remained remarkably stable with age. A major 2025 review similarly concluded that consistent age-related reductions in human NAD+ have only been demonstrated in a limited number of studies and that changes may differ between tissues.
This distinction is important because claims that everyone's NAD+ simply falls with age can overstate what human research currently shows.
Why Is NAD+ Becoming So Popular?
Growing interest in longevity research has brought NAD supplements, NAD+ precursors such as NMN and NR, and other NAD-related products into the spotlight. Researchers are investigating whether influencing NAD metabolism could have applications in healthy ageing and cellular function.
Preclinical research has produced promising findings, but evidence from human clinical trials remains considerably more limited. Researchers therefore emphasise that more clinical studies are required before firm conclusions can be drawn about the benefits of increasing NAD+ levels in humans.
For now, NAD+ research remains a rapidly developing field that connects cellular energy, metabolism, mitochondrial biology and ageing science.