The framework rests on a simple but powerful physiological observation. Every step of the oxygen cascade shows measurable age-related decline. Starting at roughly 21 percent of inspired oxygen at sea level, the partial pressure of oxygen drops sequentially across the alveoli, the arterial blood, the microcirculation, the interstitial space, and the mitochondria. In youth, this cascade is buffered by remarkable resilience: ventilation, cardiac output, capillary recruitment, and mitochondrial function adjust continuously to match oxygen supply with metabolic demand. With age, that adaptive capacity erodes at every level simultaneously. The authors emphasize that Oxygenaging is not simply a state of oxygen deficiency. Rather, it reflects a progressive loss of resilience in the mechanisms that maintain oxygen homeostasis, leaving older organisms increasingly vulnerable to mismatches between oxygen availability and energetic requirements — mismatches that compromise cellular function, tissue integrity, and physiological reserve.

The first step of the cascade, pulmonary gas exchange, deteriorates through well-characterized structural changes. Age-related loss of elastin fibers reduces lung elastic recoil, promoting premature closure of small airways, particularly in gravity-dependent regions of the lung. These poorly ventilated but still perfused units act as functional shunts, widening the alveolar-arterial oxygen gradient and increasing ventilation-perfusion heterogeneity — quantified by the log standard deviation of perfusion distribution, which rises from roughly 0.36 in younger adults to 0.47 in older individuals. Empirical reference equations established decades ago show that age is the single most robust predictor of arterial oxygenation, with arterial oxygen partial pressure falling by approximately 15 to 20 mmHg between mid-life and old age. The review also highlights a less appreciated mechanism: systemic iron deficiency, common in aging, mimics hypoxia at the pulmonary endothelium by inhibiting prolyl hydroxylase domain enzymes, exaggerating hypoxic pulmonary vasoconstriction and placing additional strain on the right ventricle.

The second step, central hemodynamics, compounds the problem. Oxygen delivery is the product of arterial oxygen content and cardiac output, and in aging the decline in maximal heart rate — dropping roughly 25 percent, from about 200 beats per minute in youth to about 150 in old age — becomes the dominant bottleneck on peak oxygen delivery. The aging system also fails to shift the hemoglobin-oxygen dissociation curve rightward at baseline to facilitate tissue oxygen unloading; because systemic 2,3-bisphosphoglycerate levels do not rise with healthy aging, tissues depend heavily on acute stressors such as the heat and acidosis of exercise — the Bohr effect — to release oxygen from hemoglobin. Combined with the flat upper plateau of the dissociation curve, which prevents healthy lung regions from over-compensating for failing ones, these deficits translate into a measurable drop in overall arterial saturation and a progressive constraint on systemic oxygen supply.

The third and arguably most consequential step occurs in the microvasculature. Maximal oxygen uptake, the integrated measure of the entire cascade, falls by approximately 10 percent per decade, limited both by reduced central delivery and by peripheral failure of oxygen extraction. Aging brings microvascular rarefaction, endothelial dysfunction with reduced nitric oxide bioavailability, and increased diffusion distances caused by fibrosis and diminished pericyte coverage. Even when bulk blood flow appears adequate, the aged microvasculature mounts a sluggish hyperemic response to exertion, failing to raise microvascular oxygen pressure precisely when the diffusion gradient into mitochondria is needed most. Notably, the authors point to a metabolic peculiarity of endothelial cells: they rely primarily on glycolysis rather than oxidative phosphorylation, and aging disrupts this specialization, crippling the migratory and proliferative machinery required for angiogenesis. This explains why simply supplementing oxygen may fail to rescue microvascular function in older tissues.

Organ-specific evidence grounds the framework in measurable clinical data. Near-infrared spectroscopy studies show regional cerebral oxygen saturation falling from roughly 69.8 percent in young adults to 62.7 percent in older adults, driven by pericyte degeneration, blood-brain barrier leakage, and uncoupling of endothelial nitric oxide synthase within the neurovascular unit. Renal BOLD-MRI reveals progressive medullary hypoxia as peritubular capillary rarefaction and tubulointerstitial fibrosis enlarge diffusion distances. In skin, transcutaneous oxygen measurements expose a blunted neurogenic vasodilatory response to thermal stress, reflecting extracellular matrix stiffness that mechanically limits vessel expansion. In skeletal muscle, phosphorus-31 magnetic resonance spectroscopy shows that post-exercise phosphocreatine recovery slows from about 37 seconds in young muscle to about 52 seconds in aged muscle, paralleled by reduced mitochondrial content, mild uncoupling via uncoupling protein 3, and instability of respiratory supercomplexes.

At the molecular level, the review describes how the hypoxia-inducible factor system — the ancient oxygen-sensing machinery conserved across metazoans — becomes maladaptive with age. In youth, prolyl hydroxylase domain enzymes use oxygen, alpha-ketoglutarate, and iron to tag HIF-1alpha for degradation, keeping the pathway exquisitely responsive to genuine hypoxia. With aging, declining NAD+ reduces SIRT1 activity and lowers von Hippel-Lindau expression, while accumulating succinate directly inhibits PHD catalytic activity. Both routes converge on the same outcome: stabilization of HIF-1alpha under normal oxygen conditions, a state the authors term chronic pseudohypoxia. This maladaptive activation suppresses mitochondrial biogenesis through the MYC-TFAM axis, impairs mitophagy through lysosomal dysfunction, and leaves a pool of damaged, reactive-oxygen-species-leaking mitochondria. The framework also intersects with iron biology — what the authors call Ferroaging — as an expanded labile iron pool catalyzes the Fenton reaction during reoxygenation, priming vulnerable cells for ferroptosis, an iron-dependent form of cell death.

The consequences ripple through metabolism and the genome. Hyperactive mTOR signaling in aging overrides HIF-1alpha’s normal metabolic brake, forcing cells to continue energy-consuming anabolic growth despite insufficient oxygen. HIF-1alpha-mediated suppression of lipolysis — the so-called lipid lock — promotes triglyceride accumulation and hepatic steatosis. Meanwhile, oxygen availability physically constrains the dioxygenase enzymes that govern the epigenetic clock: ten-eleven translocation enzymes and JmjC-domain histone demethylases all require oxygen as a co-substrate, so declining tissue oxygen pressure may directly accelerate the accumulation of aberrant methylation patterns characteristic of cellular senescence. Supporting this, the authors’ own recent work showed that intermittent hypoxia in old mice accelerated epigenetic age in lung, spleen, and heart by up to five months — an effect that reversed after return to normoxia. Hypoxia also reshapes the RNA splicing landscape, promoting intron retention and isoform switching that, when dysregulated by age-related transcriptomic noise, may generate aberrant proteins and neoepitopes that provoke immune surveillance.

The framework’s most provocative implications are therapeutic. The authors survey emerging gerotherapies that deliberately modulate the oxygen cascade: intermittent hypoxia, which in carefully dosed protocols activates neurotrophic BDNF-TrkB signaling and enhances motor recovery after spinal cord injury; hyperbaric oxygen therapy, which exploits the hyperoxic-hypoxic paradox — the rapid pressure drop from over two atmospheres back to sea level — to trigger HIF-1alpha signaling without true hypoxia, with preliminary reports of telomere elongation exceeding 20 percent in immune cells and clearance of senescent T cells; and intermittent hypoxic-hyperoxic training, which alternates low and high oxygen to drive mitophagy-based mitochondrial selection. The authors caution, however, that the hormetic dose-response curve likely shifts with age: interventions beneficial in young organisms may prove toxic in frail older adults whose NRF2-mediated antioxidant buffering is compromised. Sex differences, frailty, and individual variability in hypoxic ventilatory response further narrow the therapeutic window. Their prescription for the field is rigorous: define therapeutic windows tailored to biological rather than chronological age, monitor real-time biomarkers of oxidative stress and mitochondrial function during therapy, and conduct randomized controlled trials stratified by frailty status. Oxygen-sensing pathways, they argue, represent a high-leverage gerotherapeutic target — one that could help decouple chronological age from biological decay and chart a roadmap toward extending human healthspan.

Subject of Research: Age-related decline in the oxygen transport cascade and its role in the biology of aging

Article Title: Oxygenaging: A Physiological Framework for Geroscience

Article References: Donega, S., Fishbein, K. W., Dominelli, P., Herman, A. B., de Cabo, R., Gorospe, M., & Ferrucci, L. (2026). Oxygenaging: A Physiological Framework for Geroscience. Aging Cell, 25(9), Article e70664. https://doi.org/10.1111/acel.70664

Image Credits: AI Generated

DOI: 10.1111/acel.70664

Keywords: Oxygenaging, geroscience, oxygen cascade, HIF-1alpha, mitochondrial dysfunction, microvascular rarefaction, pseudohypoxia, ferroptosis, hyperbaric oxygen therapy, intermittent hypoxia, epigenetic aging, Aging Cell