NAD+ and Mitochondria: The Truth About Younger Cells That Ads Do Not Tell You

After your forties, you may feel that your energy is not what it used to be. You wake up tired, get more breathless than before after climbing two flights of stairs, and start wondering how to keep your body able to travel, play with your children or grandchildren, and stay independent for longer. Then you open social media and see ads for NMN and NR supplements claiming to help make your “cells younger.” The price is not small either. The question that lingers is: how true is it?

This article brings together verified evidence on NAD+, mitochondria, and two popular supplements, while stating plainly where the science is clear and where researchers are still debating. That way, you can make decisions with your doctor based on real information, not advertising claims.

What Is NAD+, and Why Are People Talking So Much About “Replenishing NAD+”?

NAD+ (Nicotinamide Adenine Dinucleotide) is like a rechargeable battery inside the cell that both supplies power and presses the button to call in the repair crew. As we age, this battery stores less charge in many tissues.

NAD+ performs two jobs in the cell at the same time. The first is redox, accepting and donating electrons in the ATP energy production chain through the electron transport chain. This is the power that fuels every cell in your body. The second is serving as a substrate for three groups of enzymes that maintain cellular health: Sirtuins, which regulate gene expression and mitochondria; PARPs, which repair DNA; and CD38, which consumes NAD+.

What makes NAD+ a key player is that all three enzyme groups compete for NAD+ from the same pool. When CD38 works hard and consumes a large amount of NAD+, less is left for Sirtuins and PARPs. DNA repair and mitochondrial maintenance can then suffer as a result. This mechanism is clearly supported by multiple peer-reviewed sources from 2014 to 2020, although part of the evidence still comes from animal experiments and some human studies, and long-term human data remain unsettled.

The strongest evidence we have right now is this cellular mechanism. We can be confident in it because multiple independent sources point in the same direction, not because it merely sounds plausible.

Mitochondria Are Easy to Damage Because mtDNA Is Fragile

Mitochondria are the power plants of the cell, and part of the fatigue you feel as you get older comes from the gradual decline in efficiency of these power plants. The main reason lies in their own DNA.

Mitochondrial DNA (mtDNA) sits close to the electron transport chain, which is a direct source of ROS, or free radicals. On top of that, mtDNA lacks the same level of protective packaging as DNA in the nucleus. It therefore accumulates mutations faster. This faster rate falls in the range of 10 to 100 times. Research has generally found 10 to 17 times, and up to 100 times in some situations, depending on the type of organism and the measurement method.

One point needs to be corrected. mtDNA is not completely naked. It is wrapped by a protein called TFAM, which acts somewhat like protective armor, but it is not the true histone armor found in the nucleus. This is a major reason mitochondria gradually decline with age. This knowledge is clearly supported by multiple independent sources.

How Are NMN and NR Different, and What Has Recent Research Found?

NMN (Nicotinamide Mononucleotide) and NR (Nicotinamide Riboside) are both precursors to NAD+. Put simply, they are raw materials the body uses to make NAD+. These are the two expensive products widely advertised as helping replenish NAD+ in cells.

Research in 2026 changed the old understanding of this issue. It was previously believed that, after ingestion, the body absorbed these compounds directly and converted them into NAD+. But work in Science Advances (PubMed 40117359) and Cuenoud et al. (Nature Metabolism January 2026, a study in 65 healthy people) found that most NMN and NR are first converted by gut microbes into nicotinic acid (NA). NA then circulates through the liver and is synthesized into NAD+ through the Preiss-Handler pathway.

Cuenoud found that this approach increased NAD+ in the blood by about twofold and maintained that increase throughout 14 days. Another study (PubMed 37463842) described the molecular mechanism by which microbes use enzymes to break down NMN before it enters NAD+ metabolism. What this means for you is that each person’s gut may respond differently to the same supplement. People with different gut microbes may get different results.

As for cellular absorption, NR enters cells through a transporter called ENT, while NMN has a specific transporter called Slc12a8, which is found in high amounts in the small intestine. That is true, but there are important details to be careful about, which are covered in the warning box below.

Points to Be Careful About: 3 Things Ads Often Do Not Tell You

Trust comes from being direct about limitations. These 3 issues are where research remains conflicting, and we will not hide them.

⚠️ Issue 1: The Numbers on NAD+ Decline With Age Are Often Exaggerated

Ads like to say that “between ages 40 and 50, NAD+ drops by half, and by age 80 it falls below 10%.” The truth can be separated into three parts.

• The claim that it “drops by about 50% in midlife” is only partly supported. A 2022 Frontiers study found that in men aged 40 to 49, NAD+ declined by about 3.4% per year, gradually, not suddenly by 50% the moment someone turns 40. In women, this decline was not found at all.
• The claim that it “falls below 10% by age 80” is not supported by evidence. Research indicates a decline of about 50% across the span from youth to age 80. Some tissues show an 80 to 90% decline, but those are tissue-specific measurements, not whole-body measurements.
• The mechanisms that make NAD+ decline (PARP, CD38, NAMPT) are clearly supported.

Researchers Peluso and colleagues (2021) even called age-related NAD+ decline a “confused consensus” because conflicting studies remain, especially in women’s blood, where many studies have not found a decline. The change appears to be specific to males and some tissues, not a universal rule for everyone.

⚠️ Issue 2: NMN Absorption Through Slc12a8 Has Not Yet Been Confirmed in Humans

The part that is true is that NR enters cells through the ENT transporter, and NMN has a specific transporter, Slc12a8, which does not transport NR and is found in high amounts in the small intestine.

The parts that remain disputed or incomplete are:

• Slc12a8 in the brain does exist according to the Human Protein Atlas database, but its level is about 100 times lower than in the small intestine, and there is still no clinical evidence that the brain can truly absorb NMN through this route.
• A 2025 study (PubMed 40117359) found that most NMN in the intestine is not absorbed directly, but is first converted by microbes into nicotinic acid. The directly absorbed portion is very small.
• The original Slc12a8 study was done in mice only, and scientists Schmidt and Brenner (2019) criticized the reliability of the data. There is still no confirmation in humans.

❓ Issue 3: Whether NR or NMN Raises NAD+ More Is Still Unanswered

Two direct comparison studies in 2026 produced conflicting results. We record both sides in line with the principle of preserving the full body of evidence.

Study	Sample	Result	Strengths and Weaknesses
Berven et al. (iScience University of Bergen)	6 people	NR 1,200 mg increased NAD+ by 161%, while NMN 1,200 mg increased it by 67% (NR was about 2.3 times higher)	crossover design and independent researchers, but the sample was very small
Cuenoud et al. (Nature Metabolism Nestlé)	65 people	NR and NMN 1,000 mg both increased NAD+ by about twofold, with no significant difference	Larger randomized sample with a control group, but funded by a supplement company

There are several possible reasons the results may differ: sample size (6 versus 65), measurement timing (8 days versus 14 days, possibly reaching steady state at different points), dose (1,200 versus 1,000 mg), each person’s gut microbes, and the fact that NAD+ measurement standards are still not universal. The conclusion is therefore “still unclear,” not a firm decision in favor of either side.

Topics That Still Need More Evidence

There are several other topics with interesting origins, but they have not yet been fully verified, so they do not count as confirmed knowledge. You should treat them with caution.

Caloric restriction and both cardio and resistance exercise have a physiological basis for helping restore mitochondria through activation of the SIRT1, AMPK, and PGC-1α pathways, as well as restoring mitophagy, the process that removes damaged mitochondria. This can be tested directly and has scientific rationale behind it, but it still awaits confirmation as core knowledge in this article.

As for CoQ10, there is a study called Q-SYMBIO that claims that in 420 patients with chronic heart failure, taking CoQ10 together with standard medication for 2 years helped reduce major adverse heart events by about half. Resveratrol, which is often advertised alongside it, has the problem that the body absorbs less than 1% into the bloodstream, and human results remain conflicting. There is still no evidence that it extends human lifespan. These two topics need further checking before conclusions can be drawn.

What We Want You to Remember, and the First Step You Can Take

The strongest evidence right now is at the cellular mechanism level: NAD+ has two roles, mitochondria become fragile with age, and the gut is the first checkpoint that converts precursors. What remains unclear is the advertising number for how much NAD+ declines, and the practical question of whether NMN or NR is better, which 2026 research is still debating internally.

This article reflects the evidence along with levels of confidence. It is not telling you whether you should or should not take anything. The decision about supplements belongs to you and your doctor. If you are considering NMN or NR, take this set of information to discuss with your doctor before spending the money, especially if you have a medical condition or are taking medications.

The first step you can take today without waiting for supplements is something with a stronger scientific foundation. Try walking for 10 minutes after dinner, and add movement that uses your muscles each week. Exercise is a way to care for your mitochondria that you can start now, for free, and with a longer evidence base than any supplement.