The Coenzyme
That Runs Out

NAD+ is not a name most people recognize. It does not get talked about on cable news. It is not in the supplement aisle next to vitamin C. But every cell in your body uses it. Without it, your mitochondria stop working, your DNA repair stops working, your basic energy chemistry stops working, and you stop working.

That should be the end of the story. Your body makes NAD+. Your body uses NAD+. The system runs. Except it does not, exactly. Sometime in your forties, your NAD+ levels begin to fall. By the time you are seventy, the levels in many tissues are roughly half what they were at twenty. The reasons are still being worked out. The trend is well-documented. And it is the reason injectable NAD+ has become one of the most-asked-about therapies in longevity medicine.

What NAD+ actually does

NAD+ stands for nicotinamide adenine dinucleotide. It is a small molecule, a coenzyme, found in every living cell. It exists in two forms: an oxidized form, called NAD+, and a reduced form, called NADH. The cell flips it back and forth as part of the chemical reactions that produce energy.

In the simplest terms, NAD+ is how your cells move electrons. Every food molecule you eat is broken down through a series of reactions. Many of those reactions transfer electrons. NAD+ accepts the electrons (becoming NADH). NADH then carries them to the mitochondria, where they are used to generate ATP, the body's energy currency. Without NAD+, the entire chain of reactions that turns food into useable energy stops.

That is only the metabolism side. NAD+ also acts as a substrate for several other classes of enzymes that govern DNA repair, gene expression, mitochondrial maintenance, and the cellular stress response. Different enzymes, different jobs, same molecule.

The decline

Cellular NAD+ levels are not stable across a lifespan. They drop. Studies in human tissues, including skin, liver, and skeletal muscle, have documented age-related decline. The exact magnitude varies by tissue and by which form of NAD is measured, but the pattern is consistent. Younger tissues have more NAD+. Older tissues have less.

The mechanisms that drive the decline are not fully resolved, but the leading candidates are clear. One is increased activity of an enzyme called CD38, which consumes NAD+ at higher rates as immune cells become more active with age. Another is the accumulated DNA damage of normal living, which activates PARP enzymes that consume NAD+ as they repair the damage. A third is reduced synthesis of NAD+ from its dietary precursors. Aging, in this view, is partly a story of NAD+ being burned faster than it can be made.

Why this matters for the rest of the body

Falling NAD+ has cellular consequences. Mitochondrial function declines because the redox cycling slows. Sirtuin activity falls, because sirtuins require NAD+ to function. DNA damage accumulates, because the repair enzymes that fix it are competing with sirtuins for the same shrinking pool. Each of these changes maps onto features of biological aging that have been documented for decades, including loss of muscle quality, declining metabolic flexibility, and reduced exercise tolerance.

This is why NAD+ has attracted the attention it has. The hypothesis, supported by a growing experimental literature, is that restoring cellular NAD+ levels can slow or partially reverse some of the age-related decline in cellular function.

How it gets replaced

Three approaches have emerged for raising NAD+ in the body. The first is dietary precursors: niacin (vitamin B3), nicotinamide riboside (NR), and nicotinamide mononucleotide (NMN). These are taken as oral supplements and are converted to NAD+ inside cells. Human trials have shown that NR and NMN can raise blood NAD+ levels, though the magnitude and durability vary across studies.

The second approach is direct injection or intravenous infusion of NAD+. This is what most longevity-clinic protocols use. The molecule is administered as a compounded preparation, often by subcutaneous injection or by IV. The pharmacokinetics differ from oral precursors: blood levels rise faster, and the dose can be controlled precisely.

The third approach is to slow the consumption of NAD+, primarily by inhibiting CD38. This is the most experimental of the three strategies, with most data still coming from animal studies.

Why injectable

For most patients, the choice between oral and injectable NAD+ is not theoretical. It is a question of bioavailability and dosing. Oral precursors are convenient and inexpensive but rely on the body's own enzymes to convert them, and the conversion can be partial. Injectable NAD+ skips the conversion entirely. The molecule that the cell uses is the molecule that arrives. This is why the longevity-medicine community has increasingly converged on injection as the preferred route for patients who want measurable changes in tissue NAD+ levels.

The trade-off is that injectable NAD+ has to be sourced from a state-licensed compounding pharmacy. There is no over-the-counter version. The 503A compounding infrastructure that has matured over the last decade is what makes the injectable option practical for individual patients.

What we know and what we don't

The science of NAD+ has matured rapidly. The decline with age is well-documented. The metabolic role is settled. The sirtuin connection is established. What is less settled is the size of the clinical effect from NAD+ replacement in healthy adults, and how long it lasts. Several human trials are underway. The early signals are encouraging but not yet definitive at the scale of the GLP-1 trials.

This is the honest middle: NAD+ is a real molecule with a real cellular role that really does decline with age. The therapy that follows is supported by the biology and is being characterized clinically. The frontier is mature enough to be safe and tested, and not yet mature enough to make breathless promises.

Where pru sits in the NAD+ conversation

At pru, NAD+ is one of the longevity therapies on our formulary because the science is strong enough to defend and the patient experience is well-characterized enough to deliver responsibly. The molecule is compounded at a 503A licensed pharmacy. Each batch ships with a Certificate of Analysis. The dose is matched to the patient.

The chemistry that has been keeping you alive since you were born can be supported, when the body's supply begins to fall, by the same molecule the body has always used. That is what responsible longevity medicine looks like. It is what we are committed to delivering.