Seven Studies, 502 Older Adults: A New Review Sorts What Hyperbaric Oxygen Can and Cannot Do

Stylised editorial illustration: a stepped teal capacity-ramp curve with amber data-point markers rising over faint lab gridlines, beside a monoplace hyperbaric chamber end-cap seen end-on with a condensation-beaded porthole ring, in cool teal and amber light

The pitch is everywhere now, in clinic brochures and wellness newsletters alike: get in the chamber, breathe pressurised oxygen, and come out with sharper thinking, better stamina and cells that behave as though they were younger. It is a seductive story, and it rests on a small number of trials. This month, a team at a Tehran physiotherapy clinic and Shahid Beheshti University of Medical Sciences tried to find out how much of it survives scrutiny.

Their answer, published in the Journal of Aging and Physical Activity on 8 October, is carefully hedged. Hyperbaric oxygen therapy (HBOT) “may improve cognitive performance in both healthy and clinical older adults” and “may offer modest benefits for physical performance,” they write — then add, in the same breath, that these findings “remain preliminary given the limited number of studies, protocol heterogeneity, and moderate methodological quality.”

What the review actually did

The work is a systematic review conducted to PRISMA standards and registered in advance on PROSPERO (CRD420251122497). Maryam Mohammadi and Amin Norouzi Fashkhami, of the Esteghlal Physiotherapy Clinic in Tehran, worked with biostatistician Alireza Akbarzadeh Baghban to search six databases — PubMed, Scopus, Web of Science, ProQuest, the Cochrane Library and Google Scholar — from inception to November 2025.

To qualify, a study had to enrol people aged 50 or older, measure cognition or physical capacity with validated instruments, and report adverse events where available. Risk of bias was scored with the modified Downs and Black checklist.

Seven studies, covering 502 participants aged 51 to 85, made the cut. Their protocols clustered tightly around clinical-grade exposures: 2.0 to 2.2 atmospheres absolute, 60 to 90 minutes per session, five to six sessions a week.

Gains that are real, or at least reported

Two high-quality studies in healthy older adults reported statistically significant improvements in global cognition, attention, executive function and processing speed, along with better aerobic capacity and pulmonary function. In clinical groups — Parkinson’s disease, cerebral small vessel disease and vascular dementia — the moderate-quality evidence suggested that HBOT added to drug treatment produced larger cognitive gains than medication alone. Physical gains in those patients, the authors note, were mostly inferred from quality-of-life and symptom scores rather than measured directly.

Four studies reported side effects. They were generally mild and self-limiting. There were no serious harms, but also no long-term safety data beyond that.

The authors then supply the caveat that matters most: follow-up ran from one to four weeks up to roughly twelve weeks. “Durability of effects” simply cannot be assessed from this evidence base.

Where the headline numbers come from

Most of the positive signal traces to a single research group and a single registered trial. The best-known study, published in Aging in 2020, randomised 63 healthy adults over 64 to HBOT or a control arm for three months. It found a significant group-by-time interaction in global cognitive function (p = 0.0017), with the largest net effects in attention (0.745) and information processing speed (0.788), plus regional increases in cerebral blood flow on perfusion MRI.

A companion randomised trial in BMC Geriatrics in 2024, with the same 63-participant, three-month design, reported improvements in maximal oxygen consumption — VO2max per kilogram rose by 1.91 ml/kg/min (net effect size 0.455, p = 0.0034) — together with rises in cardiac blood flow and blood volume. That paper lists ClinicalTrials.gov registration NCT02790541, whose original title concerns angiogenesis in the elderly rather than cognition or fitness.

The most attention-grabbing result remains a separate prospective trial of 35 healthy adults over 64, also in Aging, in which telomere length in immune cells rose by more than 20% and senescent T-helper cells fell by 37.3%. A commentary in Rejuvenation Research greeted those findings with qualified interest: the durability of the beneficial changes “is yet to be determined,” and the preliminary results “require follow-up.”

That is a fair summary of the field. The review’s own authors treat their positive findings as an invitation to run better trials, not as settled physiology.

The problem that sham-controlled trials keep finding

The reason the reviewer’s caution is warranted has less to do with molecular biology than with study design. Chambers are immersive, expensive and heavily marketed, and that combination produces strong expectancy effects — the very thing a properly blinded trial controls for.

A 2025 double-blind, placebo-controlled trial in Diving and Hyperbaric Medicine is instructive. It randomised 101 patients with Long COVID into four arms that varied both pressure and oxygen concentration, including a near-placebo arm. After treatment, there were no significant differences in subjective symptoms, functional scores or cognitive performance between any of the groups. Responses varied wildly, and some patients in the placebo arm reported substantial improvements in wellbeing. Not one of those improvements showed up in the objective outcome scores. The authors concluded that the modest benefits reported elsewhere may be attributable to expectancy.

None of that disproves a biological effect, and the Long COVID population is not the same as healthy older adults. But it does explain why a systematic review of seven studies cannot yet promote HBOT from promising to proven.

The regulatory line between therapy and marketing

It is worth being precise about what “HBOT” means legally. Hyperbaric oxygen devices are Class II medical devices cleared by the FDA through the 510(k) pathway, identifiable by Product Code CBF. Aging, cognition and physical performance are not among the cleared indications. Older adults sitting in these chambers for longevity reasons are, in the FDA’s framing, outside the intended use.

Medicare’s National Coverage Determination 20.29 makes the same distinction in reimbursement language. Coverage is limited to a defined list — carbon monoxide intoxication, decompression illness, gas embolism, gas gangrene, crush injuries, progressive necrotising infections, chronic refractory osteomyelitis, osteoradionecrosis, specific diabetic lower-extremity wounds and a handful of others — and where HBOT is covered for diabetic wounds, it applies only after at least 30 days of standard care have failed to produce measurable healing.

That list has not been extended to healthy ageing, and no committee is currently considering doing so.

There is also the safety record to weigh. In August 2025 the FDA issued a letter to health care providers after reports of fires involving HBOT devices that caused serious injuries and deaths. The agency’s recommendations were mundane and non-negotiable: train and maintain staff, follow the manufacturer’s instructions, monitor patients for the entire treatment, keep electrical and static-producing items out of the chamber, and dress patients in hyperbaric-compatible fabrics such as cotton.

For anyone weighing a course of treatment, the practical distinction is between a supervised 2.0–2.2 ATA protocol delivered in an accredited clinical facility and the 1.3–1.5 ATA “soft” sessions marketed as wellness or recovery. They are not the same intervention, they do not carry the same evidence base, and only one of them has any chance of being covered by insurance. The new review adds useful texture to the conversation about what the evidence supports. It does not settle it — and the authors, to their credit, say so.

This article reports on published research and regulatory guidance. It is not medical advice. Consult a qualified physician before considering hyperbaric oxygen therapy.

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