In 1670, the great chemist, physicist and inventor Robert Boyle was studying what happened to living tissue when exposed to extremes of pressure. He placed the eye of a viper in a sealed chamber, pumped out the air, and watched as a bubble of gas formed inside the eye. Unknown to him, this phenomenon was responsible for an illness that, centuries later, would plague divers and construction workers the world over.
Decompression sickness, also known as ‘the bends’, is a condition caused by depressurisation, such as when divers ascend to the surface or when workers exit a caisson (a pressurised container used in some construction work). This causes gasses that are dissolved in the blood to form bubbles that can block circulation, leading to a range of symptoms and potentially death.
During the construction of the Hudson River Tunnel in 1890, British civil engineer Ernest William Moir noticed that an alarming number of workers were dying from decompression sickness, and decided to do something about it. He created a pressurised airlock in which workers suffering from the the bends could undergo more gradual depressurisation. This treatment drastically reduced deaths, and was later refined by slowing the rate of decompression and by delivering 100% oxygen to the occupants of the chamber (normal air contains 21% oxygen). This practice, known as hyperbaric (above normal pressure) oxygen therapy (HBOT), wasn’t entirely new. During the 1800s, Parisian elites were using hyperbaric chambers, believing that the compressed air promoted blood circulation, cured disease and improved overall health and well-being.
Though many health and anti-ageing practices over a century old are highly questionable, perhaps the Parisians weren’t entirely wrong. HBOT does have the well established ability to treat certain diseases besides decompression sickness. Recently, there has been interest in the possibility that HBOT might even be able to slow the ageing process. Some celebrities are going so far as to buy HBOT chambers for their own homes, while some unscrupulous adverts claim that their paid HBOT sessions can cure anything from cancer to autism. What does the evidence have to say? Let’s take a look.
In normal wounds such as a cut, the abrupt loss of blood supply leads to a lack of oxygen, which acts as a signal that triggers healing. However, when the reduction in blood flow occurs over a longer period of time, such as in diabetic foot ulcers, this signal doesn’t get activated, making these wounds slow or resistant to healing.
HBOT may encourage healing of these wounds in several ways. Some wounds can no longer be reached by oxygen-carrying red blood cells, but are still being supplied with plasma, the liquid in which red cells are suspended. Most oxygen is carried by the red cells, but a small amount is carried in the plasma, and this amount is increased significantly by HBOT, thereby restoring oxygen to the tissue and helping it to heal. Increased levels of oxygen in the blood may help the immune system fight off infections, while boosting the activity of cells responsible for tissue repair and encouraging the growth of new blood vessels.
Another possible mechanism is that when a patient receives HBOT, the concentration of oxygen in healthy parts of the body increases suddenly, whereas the wounded areas are less impacted. This difference acts as a kind of wake up call, triggering the healing process and the growth of new blood vessels to restore the oxygen supply.
The ability of HBOT to improve healing has been tested for multiple conditions including burns, crush injuries, radiation injuries and vascular dementia, but most extensively in diabetic-related wounds.
Diabetic foot ulcers are slow-healing wounds with restricted blood supply that appear on the feet of people with diabetes mellitus. They are a result of damage to the extracellular matrix (the mesh that holds cells together and plays an essential role in tissue repair) and metabolic changes caused by elevated blood sugar. These wounds can be very severe and can even require amputation if infection takes hold and spreads to the bones and joints. Some randomised, placebo-controlled trials suggest that HBOT can accelerate healing and reduce the rate of amputations for diabetic foot ulcers. In 2020, researchers conducted a systematic review of 11 studies on the subject, totalling 729 participants, and concluded that while HBOT reduced the rate of major amputations, it didn’t significantly improve wound healing, though more research is probably warranted. The trials included a wide range of patients, and HBOT might be more effective in some people than in others.
Athletes often train at high altitude, where oxygen pressure is low, in order to stimulate the production of oxygen-bearing red blood cells. You would be forgiven for thinking that exposure to high levels of oxygen might have the opposite effect, however, hyperbaric oxygen therapy has in fact been explored as a means to increase exercise performance. Prolonged and repeated depletion of oxygen in the bodies of high level athletes can lead to ‘overtraining syndrome’ and increased risk of injury and illness. Receiving HBOT before, during or after exercise has the potential to increase recovery rates and allow athletes to keep their muscles active for longer. However, a recent systematic review and meta-analysis of ten studies (166 participants) on this subject concluded that HBOT only improved endurance when received during exercise, not before or after. There’s still not much data to go on when it comes to this application of HBOT, so more research is needed.
As oxygen saturation is the critical factor when it comes to keeping people hospitalised with COVID-19 alive, HBOT has been explored as a treatment for COVID in various contexts. Multiple randomised trials have found HBOT to be safe and effective for accelerating the recovery of COVID patients with low oxygen levels, and a recent systematic review of 8 trials concluded that most studies showing benefits were of good quality.
Recently, a small study involving 10 patients suggested that HBOT could also be beneficial for patients suffering from ‘long COVID’ – a poorly understood condition in which people can experience a diverse range of symptoms (such as tiredness and concentration problems) for many months following the initial infection. 10 patients who received HBOT in ten 105-minute sessions over 12 days showed significant improvements in cognitive function and reduced fatigue. However, these results are very preliminary: the trial had no control group, so all improvements could have been placebo-induced, or the patients may simply have recovered naturally.
It’s not clear through what mechanism HBOT would help long COVID patients. One possibility is that changes in long COVID caused by prolonged low oxygen are reversed by HBOT. Other theories include the patient’s immune system going into overdrive and attacking the body’s own tissues, or dormant fragments of the virus becoming reactivated. In either case, the effects of HBOT on the immune system could explain its ability to treat long COVID if this is confirmed in future trials.
So, there is plenty of evidence to back up the claim that HBOT is beneficial in certain diseases, but what about the claim that HBOT can slow the ageing process itself? If HBOT can strengthen the immune system and improve tissue repair in disease, can it also do so in healthy people, thereby delaying the development of diseases of ageing? The short answer is that we don’t really know, but there are some promising indications.
If you have been following this site, you are probably familiar with how difficult it is to determine whether a therapy actually slows ageing in humans or not. Ideally, researchers would randomise people to receive HBOT or a sham therapy on a regular basis, then follow them up for decades to see how long they lived and when they developed age related diseases. Such an experiment would be long, costly, and difficult to conduct. A more practical approach is to measure the effect of HBOT on biomarkers of ageing. These are measurable factors that are thought to correlate with a person’s true biological age.
One study looked at the effects of HBOT on telomere length. Telomeres are strings of nonsense DNA code that act as protective caps on the end of our chromosomes. Each time the DNA is duplicated during cell division, the cell’s copying machinery is unable to duplicate the very end of the DNA strand, and so a little bit of the telomere is lost. This protects important genetic information from being lost, but leaves the cell unable to divide further when the telomeres become too short. Such cells either commit suicide or become senescent ‘zombie cells’, which are thought to contribute to the ageing process.
The study took 35 healthy adults aged 64 and older and gave them daily HBOT therapy for 60 days. They took blood samples at the start of the experiment, then again after 30 sessions, 60 sessions, and 1-2 weeks after the sessions had ended. They found that the telomere length of the recipients’ white blood cells was increased by over 20% by the end of the experiment. The biggest increase was seen in B cells (the cells that produce antibodies), which saw a 37% increase in telomere length by the end of the study. They also found a significant decrease in senescent cells among some cell types.
While these are promising results, they are far from proof that HBOT slows ageing. It’s still not clear to what extent telomere shortening is a cause or consequence of ageing. In mice, genetic interventions that slow telomere shortening do seem to slow ageing, but we don’t know if this works in humans. Also, while the extent of telomere lengthening is unlikely to have been due entirely to a placebo effect, it’s worth noting that the study had no control group, and that the margins of error for telomere length were quite high. In other words, the real effect size could be much smaller than what was measured.
Other studies have looked at age-related health decline, such as reduced cognitive function, and found some benefits for HBOT. Unfortunately, many of these studies don’t use a double-blind study design (where neither the researchers nor the participants know which group of participants is the control group). This means that the control group may know that they aren’t receiving the real treatment. That’s a problem, because the nature of HBOT means there’s the potential for a large placebo effect: patients are sitting in a special chamber with an oxygen mask on a regular basis while a group of scientists monitor them.
So, while the idea that HBOT might slow ageing isn’t unfounded, it’s far from proven. We need more, higher quality studies to look at the effects of HBOT on different biomarkers of ageing and age-related diseases.
So, you’ve seen the evidence, and you’ve decided to give HBOT a try. You know that you might be wasting your money, but you’ve decided it’s worth the risk for a shot at improved health and lifespan. If so, there are a few more factors to consider.
Firstly, most at-home hyperbaric chambers and ‘hyperbaric spas’ are essentially bags that can achieve pressures 20% to 30% higher than atmospheric pressure. That’s quite low compared to most chambers used in the experiments covered in this article – the telomere length study, for example, used HBOT at 100% higher than atmospheric pressure. This isn’t to say that HBOT at these lower pressures can’t be beneficial. The problem is that there’s no scientific evidence to say that they are.
Another important consideration is safety. Though meta-analyses have found HBOT to be safe, that’s in the context of an accredited facility operated by professionals. Receiving HBOT at the wrong pressures can cause damage to the eyes and ears, however the most dangerous aspect of HBOT by far is the risk of fire. Pressurised oxygen is extremely flammable, and so a spark from static electricity or an electronic device is enough to cause a fatal explosion (this happened at a clinic in Florida in 2009). Poorly designed chambers may explode. Some people have given themselves the bends in their own hyperbaric chambers. Would you trust a ‘hyperbaric spa’ to have taken the necessary safety precautions against these hazards?
Some experts argue that even when performed in a medical facility, HBOT shouldn’t be offered as an anti -ageing treatment, and that we should prioritise caution until more evidence is available.
So, is HBOT as an anti-ageing therapy supported by the evidence, or is it pseudoscience? HBOT does have a firm basis in scientific research, but as is the unfortunate case with many anti-ageing treatments, that research sometimes gets stripped of context or exaggerated by those with a financial incentive to do so. HBOT is beneficial for wound healing and in specific age-related diseases, but it’s too early to conclude that it slows ageing. Even if it does, the pressurised bag you bought from Amazon might not do the trick. And if any business tells you that their HBOT sessions can get rid of your wrinkles or cure your child’s autism, ask them to show you their randomised controlled trials before you give them your money!
Are hyperbaric chambers really a fountain of youth? https://www.popsci.com/health/hyperbaric-chambers-anti-aging-science/
So You Want to Pop Into a Hyperbaric Oxygen Chamber to Rid Yourself of Wrinkles?: https://www.mcgill.ca/oss/article/health-pseudoscience/so-you-want-pop-hyperbaric-oxygen-chamber-rid-yourself-wrinkles
A systematic review and meta-analysis of hyperbaric oxygen therapy for diabetic foot ulcers with arterial insufficiency: https://doi.org/10.1016/j.jvs.2019.07.082
Effects of Pre-, Post- and Intra-Exercise Hyperbaric Oxygen Therapy on Performance and Recovery: A Systematic Review and Meta-Analysis: https://doi.org/10.3389/fphys.2021.791872
Hyperbaric oxygen as an adjuvant treatment for patients with COVID-19 severe hypoxaemia: a randomised controlled trial: http://dx.doi.org/10.1136/emermed-2021-211253
The effects of hyperbaric oxygen therapy (HBOT) on coronavirus disease-2019 (COVID-19): a systematic review: https://doi.org/10.1186/s40001-021-00570-2
Hyperbaric oxygen therapy for the treatment of long COVID: early evaluation of a highly promising intervention: https://doi.org/10.7861/clinmed.2021-0462
Hyperbaric oxygen therapy increases telomere length and decreases immunosenescence in isolated blood cells: a prospective trial: https://doi.org/10.18632/aging.202188
Telomerase gene therapy in adult and old mice delays aging and increases longevity without increasing cancer: https://doi.org/10.1002/emmm.201200245
Cognitive enhancement of healthy older adults using hyperbaric oxygen: a randomized controlled trial: https://doi.org/10.18632/aging.103571