The 12 Hallmarks of Aging: What Scientists Actually Mean

Written by the Nuvirox Research Team

Short answer: the hallmarks of aging are twelve cellular processes that researchers agree get worse with age, can be made worse experimentally, and can — at least in animals — be improved by intervention. They were proposed as nine in 2013 and expanded to twelve in 2023. They are a research framework, not a treatment plan, and the honest reading is that we can measure all twelve far better than we can fix any of them in humans.

Almost every longevity headline you have read is downstream of this framework. When a study says a compound “targets aging,” it usually means it moves one hallmark in one tissue in one species. That is worth knowing before you read the next one.

Grouping follows the structure used in the 2013 and 2023 reviews. The categories are conceptual, not sharp boundaries — the authors emphasise that the hallmarks are heavily interconnected.

What makes something a “hallmark” rather than just a feature of getting old?

Three criteria, and they are strict. A hallmark has to appear with normal aging, has to accelerate aging when you experimentally worsen it, and has to slow or reverse aging when you intervene on it. That third criterion is what separates a hallmark from a bystander.

It is also where the framework is most vulnerable. The reversal criterion has been met convincingly in yeast, worms, flies, and mice. In humans it has been met for almost nothing, because we do not run 40-year randomized trials with mortality endpoints.

Which hallmarks actually relate to feeling tired?

Two, mainly. Mitochondrial dysfunction describes the age-related decline in the organelles that generate most of your ATP — fewer of them, less efficient, more prone to leaking reactive oxygen species. If you want the ground-level version of how that machinery works, we walk through it in our explainer on how your cells actually make energy.

Deregulated nutrient-sensing is the other one. This covers the pathways that read cellular fuel status and decide whether to build or conserve — insulin/IGF-1 signalling, mTOR, AMPK, and the sirtuins. NAD+ sits inside this hallmark because sirtuins cannot function without it, a relationship we cover in more depth in our piece on sirtuins and NAD+.

The remaining ten matter enormously for disease risk. They just do not map cleanly onto the subjective experience of low energy, and articles that claim otherwise are usually reaching.

Worth noting that the nutrient-sensing hallmark is about signalling rather than fuel supply. NAD+ is not burned as an energy source — it shuttles electrons and acts as a substrate for signalling enzymes, a distinction we unpack in our comparison of NADH and NAD+.

Why did nine become twelve?

The 2023 update added three: disabled macroautophagy, chronic inflammation, and dysbiosis. Autophagy had previously been folded into loss of proteostasis; the authors separated it because the evidence for its independent role had grown. Chronic inflammation had been part of “altered intercellular communication,” and the gut microbiome had not been treated as a hallmark at all.

This is worth noticing for a reason that has nothing to do with biology: the framework changes. It is a consensus document written by five researchers, extremely well cited and extremely useful, but it is a map rather than the territory. Other groups have proposed different lists, including mechanical property changes and splicing dysregulation.

What human studies actually show

Caloric restriction slowed one measure of biological aging in a randomized trial — and moved two others not at all. The CALERIE trial randomized 220 adults without obesity to 25% caloric restriction or an ad libitum diet for two years. A later analysis found the restriction group slowed on the DunedinPACE pace-of-aging algorithm by roughly 2–3%. The PhenoAge and GrimAge clocks showed no significant change. This is the single best human test of the idea that a hallmark-targeting intervention shifts measured aging, and the result is real but small and inconsistent across measures.

NAD+ precursors raise NAD+ reliably; the downstream effects are less certain. A 2×6-week randomized crossover trial in healthy middle-aged and older adults found 1,000 mg per day of nicotinamide riboside was well tolerated and clearly elevated NAD+ metabolism. Blood pressure and arterial stiffness showed a promising secondary signal that the authors explicitly flagged as needing dedicated follow-up trials.

The honest counterweight: a well-run trial found nothing on its primary outcome. A randomized placebo-controlled trial gave 2,000 mg per day of nicotinamide riboside to obese men for 12 weeks. It confirmed safety. It did not improve insulin sensitivity, and it did not produce the lipid-mobilising effects the animal literature had predicted. Raising a molecule is not the same as changing a phenotype, and this trial is the cleanest demonstration of that gap.

What the hallmarks framework won't do

It will not tell you your personal risk. The hallmarks are population-level biology, and the leap from “this process declines with age” to “this process is why you feel the way you do” is a leap, not a step.

It also will not validate a supplement. A product that plausibly touches a hallmark has cleared a mechanistic bar, not a clinical one. Several compounds with good hallmark stories — we have covered urolithin A, spermidine, and taurine individually — have human data ranging from modest to genuinely contested.

And it will not explain persistent fatigue. If you are tired for months, the differential a clinician works through is anaemia, thyroid dysfunction, sleep apnoea, depression, medication effects, and inflammatory disease — not epigenetic drift. See a doctor before you see a supplement label.

So what is actually actionable here?

Three things have randomized human evidence touching more than one hallmark: structured exercise, adequate sleep, and not being in energy surplus. That is unglamorous and it is what the data supports.

Beyond that, the interventions with the most human trial evidence per hallmark are narrow. NAD+ precursors have the largest human dataset among the nutrient-sensing compounds, which is why they get disproportionate attention — not because the effect sizes are large, but because someone actually ran the trials.

Frequently asked questions

Are the hallmarks of aging proven?

The framework is well-accepted as a description; the causal claims are stronger in model organisms than in humans. All twelve are observed in aging humans. The claim that intervening on them extends human healthspan remains largely untested in long randomized trials.

Which hallmark is the most important?

The authors decline to rank them, and deliberately so — they argue the hallmarks are interconnected, so improving one often affects others. Genomic instability and epigenetic alterations sit upstream of several of the rest, which is why they attract the most basic research funding.

Can supplements target the hallmarks of aging?

Some plausibly touch specific hallmarks in mechanistic studies. NAD+ precursors relate to nutrient-sensing and mitochondrial function; senolytics target cellular senescence. Human outcome data is thin for all of them, and no supplement has been shown in a randomized trial to extend human lifespan.

Is biological age testing based on the hallmarks?

Partly. Epigenetic clocks measure the “epigenetic alterations” hallmark specifically, which is one of twelve. We look at how well those tests perform in our review of biological age test accuracy.

From Nuvirox

Why we formulated NAD+ Restore.

Every two-capsule serving delivers 500 mg of nicotinamide riboside chloride (NR) — one of the two most-researched NAD+ precursors, within the dose range used in published human trials.

It also includes 150 mg trans-resveratrol from Japanese knotweed and 50 mg quercetin from Sophora japonica — polyphenols studied alongside NAD+ pathways for cellular health support — plus 10 mg galactomannans from fenugreek to support absorption.

It ships with a 60-day money-back guarantee, which is long enough to actually evaluate it the way the research says you should.

Learn more about NAD+ Restore →

The bottom line

The hallmarks of aging are the best organising framework biology currently has for why bodies wear out, and the 2023 expansion to twelve reflects a field that is still moving. Read them as a research agenda rather than a shopping list. The gap between “we can measure this hallmark” and “we can change this hallmark in a person, and it matters” is where nearly all the honest uncertainty in longevity science currently lives.

References

1. López-Otín C, Blasco MA, Partridge L, Serrano M, Kroemer G. Hallmarks of aging: an expanding universe. Cell. 2023;186(2):243–278. doi:10.1016/j.cell.2022.11.001. PMID: 36599349.
2. López-Otín C, Blasco MA, Partridge L, Serrano M, Kroemer G. The hallmarks of aging. Cell. 2013;153(6):1194–1217. doi:10.1016/j.cell.2013.05.039. PMID: 23746838; PMCID: PMC3836174.
3. Tartiere AG, Freije JMP, López-Otín C. The hallmarks of aging as a conceptual framework for health and longevity research. Front Aging. 2024;5:1334261. doi:10.3389/fragi.2024.1334261. PMID: 38292053; PMCID: PMC10824251.
4. Waziry R, Ryan CP, Corcoran DL, et al. Effect of long-term caloric restriction on DNA methylation measures of biological aging in healthy adults from the CALERIE trial. Nat Aging. 2023;3(3):248–257. doi:10.1038/s43587-022-00357-y. PMCID: PMC10148951.
5. Martens CR, Denman BA, Mazzo MR, et al. Chronic nicotinamide riboside supplementation is well-tolerated and elevates NAD+ in healthy middle-aged and older adults. Nat Commun. 2018;9:1286. doi:10.1038/s41467-018-03421-7.
6. Dollerup OL, Christensen B, Svart M, et al. A randomized placebo-controlled clinical trial of nicotinamide riboside in obese men: safety, insulin-sensitivity, and lipid-mobilizing effects. Am J Clin Nutr. 2018;108(2):343–353. doi:10.1093/ajcn/nqy132. PMID: 29992272.

These statements have not been evaluated by the Food and Drug Administration. This product is not intended to diagnose, treat, cure, or prevent any disease. This article is for informational purposes only and is not a substitute for professional medical advice.