NAD (nicotinamide adenine dinucleotide) is a molecule found in every living cell that plays a central role in converting food into energy. It also helps maintain DNA, regulate cellular aging, and keep your metabolism running properly. Without it, your cells would stop producing energy within minutes. NAD levels naturally decline with age, which has made it one of the most studied molecules in aging research.
How NAD Works in Your Cells
NAD exists in two forms that constantly swap back and forth: NAD+ (the oxidized form) and NADH (the reduced form). Think of NAD+ as an empty shuttle bus and NADH as that same bus carrying passengers. During digestion, your cells break down glucose and other nutrients. NAD+ picks up electrons (the “passengers”) from those nutrients and becomes NADH. That NADH then delivers those electrons to your mitochondria, the power-generating structures inside cells, where they’re used to produce ATP, your body’s primary energy currency.
This cycle is remarkably productive. A single molecule of glucose can generate up to eight NADH molecules inside the mitochondria, each one carrying electrons that ultimately drive ATP production. NAD+ is the primary electron acceptor during the initial breakdown of sugar, while NADH is the primary electron donor that fuels the final energy-producing step. The ratio of NAD+ to NADH in your cells reflects your overall metabolic and energy status.
NAD+ Does More Than Make Energy
Beyond energy production, NAD+ serves as a raw material for two families of enzymes that handle critical maintenance work. The first group, called sirtuins, use NAD+ to regulate gene expression, control inflammation, and help cells respond to stress. Sirtuins work by removing chemical tags from proteins, a process that requires NAD+ to function. They’re often described as “longevity regulators” because of their role in cellular health.
The second group, called PARPs, use NAD+ to repair damaged DNA. When your DNA breaks (which happens thousands of times a day from normal wear and tear), PARP enzymes consume NAD+ to build repair signals at the damage site. The catch is that heavy DNA damage can drain NAD+ reserves quickly. When PARP activity is high, it depletes the NAD+ available for sirtuins, creating a tug-of-war between DNA repair and other protective functions. This competition becomes more consequential as you age and NAD+ levels drop.
NAD+ Declines Significantly With Age
NAD+ levels don’t stay constant throughout life. Research measuring NAD+ in human tissues has found consistent declines across multiple organs. In human skin, average NAD+ concentration appears to drop by at least 50% over the course of adult aging. Human liver samples from people over 60 show roughly a 30% decline compared to people under 45. Brain imaging studies have found decreases ranging from 10% to 25% between young adulthood and old age, and cerebrospinal fluid shows about a 14% decline in people over 45 compared to younger adults.
This decline matters because lower NAD+ means less fuel for energy production, DNA repair, and the protective sirtuin pathways. Researchers believe the age-related drop in NAD+ contributes to many hallmarks of aging, including mitochondrial dysfunction, accumulated DNA damage, and chronic inflammation.
How Your Body Makes NAD+
Your body produces NAD+ through three distinct pathways, each starting from a different raw material. The first is the de novo pathway, which builds NAD+ from scratch using tryptophan, an amino acid found in protein-rich foods. The second is the Preiss-Handler pathway, which converts nicotinic acid (a form of vitamin B3) into NAD+. The third is the salvage pathway, which recycles nicotinamide, a byproduct released whenever sirtuins or PARPs consume NAD+. This recycling route is the most active of the three and keeps NAD+ levels topped off on a day-to-day basis.
Your daily NAD+ needs can be met with dietary tryptophan or roughly 15 mg of niacin per day. Meat, fish, and dairy products are the richest sources of niacin and its precursors. Some plant foods also contain newer precursors that feed into the salvage pathway: cucumbers, cabbage, and immature soybeans contain small amounts of nicotinamide mononucleotide (NMN) and nicotinamide riboside (NR).
NAD+ Precursor Supplements
Because NAD+ itself is a large molecule that breaks down in the digestive tract, supplements typically use smaller precursor molecules that your body can convert into NAD+. The two most popular are NMN and NR. Both feed into the salvage pathway and bypass a key bottleneck enzyme whose activity slows with age, which is why they’ve attracted so much interest as potential anti-aging interventions.
A randomized, double-blind clinical trial involving 80 healthy middle-aged adults tested daily oral doses of 300 mg, 600 mg, and 900 mg of NMN over 60 days. All three doses raised blood NAD+ concentrations, and no safety concerns were identified at any dose level. NR has similarly been tested in multiple human trials and is generally well tolerated. However, the long-term effects of sustained NAD+ boosting in humans are still being studied, and it’s not yet clear whether raising NAD+ levels translates into the lifespan or healthspan benefits seen in animal research.
As of late 2025, the FDA reversed its earlier position and confirmed that NMN qualifies as a dietary supplement in the United States. Companies selling NMN products still need to submit premarket safety notifications, and products without proper filings remain subject to enforcement. NR has been available as a supplement for several years and holds generally recognized as safe (GRAS) status.
IV NAD+ Therapy
Some clinics offer intravenous NAD+ infusions, typically marketed for energy, mental clarity, or addiction recovery. The science here is thinner than the marketing suggests. Early studies in Parkinson’s patients using intravenous NADH (the reduced form) found that about 60% of patients experienced moderate improvement in disability, but these were small, older studies without placebo controls. How the body actually processes NAD+ delivered directly into the bloodstream isn’t fully understood. It likely gets broken down into nicotinamide and other fragments by the liver, meaning IV delivery may ultimately work through the same salvage pathway that oral precursors use.
No large, well-controlled trials have directly compared IV NAD+ to oral precursor supplements in healthy adults. The cost difference is substantial: IV sessions typically run hundreds of dollars per infusion, while oral NMN or NR supplements cost a fraction of that monthly. Without strong evidence that IV delivery offers a meaningful advantage, the premium is hard to justify on scientific grounds alone.