NAD+ Precursor
NAD+ precursors are molecules that can be converted into NAD+, a vital coenzyme found in all living cells, crucial for energy production, cellular repair, and longevity. Taking NAD+ directly is generally considered inefficient due to its inability to enter cells directly due to its large size and polar nature, making it unable to cross the cell membrane effectively. Thus, NAD+ precursors like NMN, NR, and NA, which are smaller and can enter cells more easily, are used to increase cellular NAD+ levels, as they can be converted into NAD+ once inside the cells. These precursors are therefore preferred for supplementation to boost NAD+ levels efficiently within the body.
- Nicotinamide Mononucleotide (NMN): A prominent NAD+ precursor, NMN, is involved in the biosynthesis of NAD+. NMN enters cells via specific transporters and is converted to NAD+ through a series of enzymatic reactions.
- Nicotinamide Riboside (NR): Another significant precursor, NR, is converted into NMN before participating in NAD+ synthesis. NR can enter cells through unique transporters and is phosphorylated to NMN by the enzyme NR kinase.
- Nicotinamide (NAM): NAM, a form of vitamin B3, is also a precursor of NAD+, contributing to its synthesis through the salvage pathway. NAM is converted to NMN by the enzyme nicotinamide phosphoribosyltransferase (NAMPT).
- Nicotinic Acid (NA): NA, another form of vitamin B3, serves as a precursor of NAD+ through the Preiss-Handler pathway. NA is converted to NAD+ via a series of enzymatic reactions, first to nicotinic acid mononucleotide (NAMN), then to nicotinic acid adenine dinucleotide (NAAD), and finally to NAD+.
- Reduced Nicotinamide Mononucleotide (NMNH): A new and efficient NAD+ precursor, NMNH operates via a novel metabolic pathway that is independent of the enzymes NRK (Nicotinamide Riboside Kinase) and NAMPT (Nicotinamide Phosphoribosyltransferase).
Comparision
| Precursor | Nicotinamide Mononucleotide (NMN) | Nicotinamide Riboside (NR) | Nicotinamide (NAM) | Nicotinic Acid (NA) |
|---|---|---|---|---|
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| Description | A vital NAD+ precursor involved in the biosynthesis of NAD+. NMN enters cells via specific transporters. | A significant precursor that is converted into NMN before participating in NAD+ synthesis. NR can enter cells through unique transporters. | A form of vitamin B3 and a precursor of NAD+, contributing to its synthesis through the salvage pathway. | Another form of vitamin B3 serving as a precursor of NAD+. |
| Pathway | NAD+ salvage pathway | NAD+ salvage pathway | Salvage Pathway | Preiss-Handler Pathway |
| Conversion Process | Converted directly to NAD+ through a series of enzymatic reactions. | Phosphorylated to NMN by the enzyme NR kinase, then converted to NAD+. | Converted to NMN by the enzyme nicotinamide phosphoribosyltransferase (NAMPT), then to NAD+. | Converted to NAD+ via a series of enzymatic reactions: NA → NAMN → NAAD → NAD+. |
| Molecular Weight | 334.22 g/mol | 255.25 g/mol | 122.13 g/mol | 123.11 g/mol |
| Bioavailability | Currently under investigation, but shows promise in preliminary studies | Good bioavailability when taken orally | Lower bioavailability compared to NMN and NR | Well-established bioavailability |
| Safety and Toxicity | Considered safe at moderate doses; long-term effects still under investigation | Generally regarded as safe; high doses may cause mild side effects | Generally safe; excessive amounts may cause flushing and other side effects | Safe at recommended doses; high doses may cause flushing |
| Natural Sources | Not found in significant amounts in food | Found in trace amounts in milk | Found in meat, fish, and grains | Found in meat, fish, and grains |
| Research Status | Extensively studied in animals; human research is ongoing | Well-studied in both animals and humans | Extensively researched | Extensively researched |
| Cost and Accessibility | Relatively expensive; widely available as a supplement | Moderate cost; widely available as a supplement | Less expensive; widely available in both food and supplement form | Least expensive; widely available in both food and supplement form |
| Half-Life | Not well-established; more research needed | Short, around 2.7 hours in humans | Longer than NMN and NR | Long, around 5.6 hours in humans |
| Clinical Trials | Several ongoing to determine efficacy and safety in humans | Numerous completed and ongoing, showing promising results for various health conditions | Extensively studied, with numerous trials completed | Extensively studied, with numerous trials completed |