Sirtuins and NAD+: why do cell repair proteins share one supply?
Protective proteins and DNA repair both spend NAD+. Another protein uses more with age, leaving less for those jobs.
What are sirtuins, and why do they need NAD+?
You nick a finger on a screen door and watch the cut close. Repair takes energy and many kinds of cell work.
Sirtuins are proteins that help cells handle strain and keep house. Each time they work, they use some NAD+.
DNA repair proteins draw from the same supply. A third protein also uses more of it as the body ages.
That shared supply is the key point. When DNA repair uses more, the sirtuin proteins have less available for their own cell-care work, and the reverse can also happen inside the same tired cell that day.
Group 01: What do sirtuins do with NAD+?
Sirtuins help cells cope with strain [5]. They use one bit of NAD+ each time they change how another protein works [9].
When the supply falls, that protective work can slow. Liver cells also need NAD+ delivered to the parts that make energy [13].
In mice, cutting off that delivery weakened cell defenses and caused liver fat to build up. That result hasn't proved a health gain from pills in people.
A major medical review found that sirtuins spend NAD+ while doing cell care [8]. The finding explains the need for fuel; it doesn't prove a treatment.
Group 02: Why can DNA repair use so much NAD+?
A DNA repair protein called polymerase 1 starts work when DNA breaks [9]. It uses NAD+ while building the patch [5].
Sun and normal cell strain can cause many small breaks at once. A rush of repair may leave less NAD+ for sirtuins [8].
Medical reviews describe those two jobs as users of one supply [5]. Neither group has its own private tank.
When the level drops, several kinds of cell care feel it [8]. Urgent DNA repair takes priority over routine upkeep.
That trade-off helps explain why researchers track the shared supply. It doesn't tell us that taking more will improve repair in a person.
Group 03: How does the CD38 protein drain NAD+ with age?
A third protein sits on the outside of cells and rises with age [11]. Called CD38, it breaks down NAD+ and leaves less for cell care [2].
Mice bred without that protein kept higher NAD+ levels when old [2]. The result came from mice, so it doesn't prove that blocking the protein helps people.
The mouse test did show that faster use can drive the age-related drop [11]. Slower making isn't the whole cause.
The CD38 protein that uses NAD+ is like a leak in a gas tank. Adding more fuel won't answer why the leak grew.
How does the body turn used pieces into fresh NAD+?
Tissues gather used pieces and rebuild NAD+ [10]. A pace-setting protein follows the body's 24 hour clock [7].
In mice, blocking that protein upset 89% of daily patterns in brown fat, the kind that burns energy to make heat. That figure means most of the measured daily patterns changed.
The same mouse test upset 77% of patterns in white fat, which stores energy [7]. Muscle kept its usual daily pattern.
That difference means each tissue controls fuel in its own way. A result in mouse fat can't set the best time for a person's pill.
Old cells can also leave tissue sore and swollen. The recycling protein affects that swelling, so simply adding more fuel may not help [6].
What has NAD+ therapy proved in people?
NAD+ therapy is a sales term, not an approved treatment. Pills made from smaller pieces raised blood levels in human tests [4][3].
Clinic drips have much weaker proof. Most of the liquid was gone after two hours [12].
Pharmacies that mixed shots to order also faced recalls after germs tainted vials. That is a risk of the mixed liquid and the needle.
Giving sirtuins more fuel makes sense in a lab. A 2025 review found that a clear gain in people's health remains unproved [14].