I've heard that scuba diving, over time, is damaging to the brain. Any truth to that?
I hadn't heard that regular, safe, within-the-limits scuba diving could cause brain damage, so I researched it, and here's what I found. Around 2000, a landmark study was published that compared the MRI scans of recreational divers to those of non-divers. The two groups were closely matched for age, size, fitness and other variables. The big difference was that one group dived; the other didn't. The divers unfortunately had five times more brain lesions than the non-divers. The story made headlines; scuba diving was unsafe.
A few years later, another study compared professional divers to non-divers. Instead of looking at brain damage on MRI, this study used neuro-psychiatric tests. Memory, attention, and calculation skills were tested, and no significant differences were found. Scuba diving was safe, after all.
Critics argued that such tests were not sensitive enough to pick up mild damage. Supporters countered that if a brain lesion was so minor that it produced no symptoms, it was insignificant.
The most recent important study came a few years ago, when a large number of healthy professional divers were given MRI scans.
Divers had twice as much brain scarring as non-divers, even if they hadn't ever had a single episode of the bends or other dive-related injury.
The evidence seems to be mounting that, unsurprisingly, breathing highly pressurised gases at depth isn't good for our brains. Teensy bubbles dissolve in our bloodstream and tissues at 30m depth quadruple in size as we ascend. Most get exhaled, but some of that dissolved gas gets stuck in capillaries, damaging them.
This bubble expansion happens to some degree on every ascent, even the slow and safe ones. We feel no pain, but the MRI shows the cumulative effects years later. Given that millions of people dive worldwide, the risk is trivial for most, but still worth knowing about.