NAD+ is widely present in all human cells. It is an important cofactor for Sirtuins protease and CD38 polymerase. It participates in redox reactions and is the core of cellular energy metabolism. It directly or indirectly affects many key cellular functions.
The reason why NAD+ levels decrease with age is because it participates in many important metabolic reactions. Mainly from three aspects:
(1) As we age, DNA damage accumulates. DNA damage activates PARPs enzymes. PARPs consume NAD+ to repair damaged DNA.
(2) Enzymes in the immune system also consume NAD+. The more active the immune system is, the more NAD+ is consumed.
(3) There is an important class of enzymes called sirtuins, which play an important role in maintaining chromosome stability and DNA repair. DNA damage and chromosomal instability accumulate with age, causing sirtuins to consume more NAD+.
NAD+ synthesis is mainly divided into two types, including the de novo synthesis pathway and the salvage synthesis pathway.
1. The de novo synthesis pathway is that the human body itself produces NAD+ in the cytoplasm through tryptophan, and tryptophan can be obtained from foods such as meat, cheese, eggs, and fish.
2. The salvage synthesis pathway is to directly supplement NAD+ precursors, such as nicotinic acid (NA), Nicotinamide Mononucleotide (NMN) and nicotinamide riboside (NR), among which NMN has the highest conversion efficiency.
As an important coenzyme and energy production medium in the human body, NAD+ has a huge impact on many functions of the body.
References; Anthony J. Covarrubias, Rosalba Perrone, Alessia Grozio & Eric Verdin. NAD+ metabolism and its roles in cellular processes during ageing. Nature Reviews Molecular Cell Biology. 22 December 2020.s41580-020-00313-x.
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