Hypoxia/Hypoxemia – low oxygen level in the tissues/low oxygen level in the blood

I always thought climbing Mt Everest was an incredibly hard task - but just in the moment.

Once it is over normal life can resume.

But when I read Ben Fogle’s account I realised there was much more to it.
He talked about the lingering effects for months on his brain function and cognition from sustained hypoxia – shortage of oxygen .

At the summit of Everest, oxygen levels are about one-third of those at sea level. Even with supplemental oxygen, the brain receives far less oxygen than it’s evolved to handle.

MRI scans of climbers after high-altitude expeditions have shown:

1) White-matter changes (similar to those seen after small strokes or concussions).

2) Shrinkage in parts of the brain, such as the hippocampus (which supports memory and spatial navigation).

3) Measurable cognitive deficits (slower reaction times, reduced short-term memory, poorer concentration).

4) Some of these changes reverse over weeks or months, but in certain cases they persist for years.

So, if too little O2 can cause cognitive decline can too much O2 remedy it?

There’s growing interest in whether oxygen therapy (especially hyperbaric oxygen therapy — HBOT) can help cognitive decline and dementia.

Short answer: promising but not definitive.

Some randomized trials and several clinical studies report cognitive improvements after HBOT in people with vascular cognitive impairment, post-stroke cognitive deficits, long-COVID brain fog and early Alzheimer’s-type disease.

These studies show improvements on neurocognitive tests and imaging markers (increased cerebral blood flow, improved white-matter integrity).

How it might work:

1) Increased oxygen delivery transiently raises tissue O₂, supporting energy metabolism in hypoxic brain regions.

2) Angiogenesis (the process by which new blood vessels form from existing ones): HBOT can induce new micro blood vessels and increase cerebral blood flow in injured or aged tissue.

3) Anti-inflammatory and anti-apoptotic effects, plus stimulation of stem cells and mitochondrial biogenesis, have been shown in animal models and small human studies.

There is an interesting overlap between artery damage (cardiovascular disease) and brain tissue degeneration (dementia) that isn’t just about blood flow — it’s deeply linked through inflammation and blood vessel damage.

Many suspect the focus of dementia research on amyloid plaque a Red Herring - again found at the scene of the crime but “not guilty your Honour”.