“Hyperbaric oxygen therapy reverses aging”

Hyperbaric oxygen therapy means breathing pure oxygen inside a sealed chamber pressurised above normal air pressure, usually for about an hour a day. The claim that it reverses ageing rests on three trials in healthy older adults, all run at the same hyperbaric centre in Israel.

The study that made the headlines gave 60 daily sessions to 35 healthy adults aged 64 and over and tested their blood before, during and after [1]. Telomeres - the protective caps on the ends of chromosomes, which shorten as cells divide over a lifetime - came out more than 20% longer in four types of immune cell. Worn-out cells declined too: senescent T helper cells fell 37% and senescent cytotoxic T cells fell 11% [1]. Senescent cells have stopped dividing but have not died off, and they build up with age.

Everyone in that study was treated. With no comparison group there is no way to know what the same markers would have done over three months without the chamber, and results varied enough between people that some barely moved [1].

The cognition trial is the strongest of the three, because it had a control group. 63 healthy adults over 64 were split at random: 33 did three months of sessions, 30 did nothing [2]. The treated group scored better on general thinking ability afterwards, with the biggest gains in attention and processing speed, and brain scans showed more blood reaching several regions at the front of the brain. Nobody was given a dummy chamber session, so knowing you are the one being treated cannot be ruled out of the result.

The third trial looked at skin instead of blood. Thirteen men averaging 68, drawn from a 70-person ageing cohort at the same centre, spent three months with no treatment and then three months in daily sessions. Their skin samples afterwards showed denser collagen, longer elastic fibres, more small blood vessels and fewer senescent cells in the tissue [3].

The idea behind all of it is that repeatedly raising oxygen and then dropping back to normal air tricks the body into the repair response it normally saves for when oxygen runs short [1].

Who the evidence does not cover:

• adults under 60 - every one of these trials enrolled people aged 64 and up
• women, for the skin findings, which came from 13 men [3]
• anyone being treated for an illness - these were healthy volunteers

There are side effects, and they are not rare. A retrospective review of 2,334 patients treated at the same Israeli centre recorded an adverse event in 17% of them, most commonly middle ear barotrauma, a pressure injury to the eardrum, in about 9% [4].

None of this tests the claim itself. Reversing ageing would mean living longer or staying healthy for longer, and no trial here followed anyone past three months. What was measured is telomere length in blood, blood flow on a brain scan and collagen in a skin sample, in groups of 35, 63 and 13 people at one centre, and no independent laboratory has repeated any of it.