Joseph Dituri went into the water at 73 inches tall. He came out, 100 days later, at just over 72.

The final measurement came on a Key Largo dock in June 2023, in front of family, friends and strangers who had followed the mission online, the St Pete Catalyst reported from the scene. Dituri, an associate professor at the University of South Florida and a retired US Navy saturation diving officer, had just finished a stint in a 100-square-foot habitat parked 22 feet beneath a lagoon, a mission the university announced as complete the morning he surfaced.

He had come out shorter.

How the habitat differs from a submarine

Jules’ Undersea Lodge holds the sea out with nothing but air. A submarine keeps its interior at about the pressure you would feel standing on the pier. The lodge instead matches the water pressing on it, with air pumped in continuously to keep the lagoon out, a setup that puts the inside at about 1.6 times surface pressure, Smithsonian magazine explained.

That is not a crushing load. It is about what a snorkeller feels a few metres down, and a healthy body copes with it for months.

Height dips a little over an ordinary day too. Gravity presses down while you are upright, the discs lose some water, and you regain it lying down overnight. That mechanism does not obviously explain what happened to Dituri, though. The extra pressure in the lodge was hydrostatic, pressing on him from every direction at once rather than down through the spine alone. His doctors documented the missing half inch, or 1.3 centimetres, when he surfaced, but the exact chain from pressurised days to a shorter spine was never spelled out, Yahoo News noted.

He later told NPR that he reckoned he had lost closer to three-quarters of an inch, which tells you something about the precision of measuring a man on a dock while people applaud.

Does height ever move the other way?

It does, though the mechanism has nothing to do with pressure: cabin air on the International Space Station sits close to sea-level. Scientific American has documented that NASA crews can gain up to 3 per cent in height in microgravity, enough to add two inches to a six-foot astronaut, because gravity’s usual pull on the spine goes away, letting the discs swell and the vertebrae drift apart. That gain is a loan rather than a gift, and the spine settles back to its old dimensions within months of landing.

Dituri pitched his own mission at the same audience. “We’re going to fly from Earth to Mars,” he told InsideHook mid-mission, adding that the best transfer window runs about six months each way. A high-pressure box, cut off from the surface, was his stand-in for that kind of isolation.

The claims that went past the tape measure

“So far, preliminary example is that stress overall in my body has decreased,” Dituri told NPR after he surfaced. His doctors also documented a 72-point fall in cholesterol, inflammatory markers cut by around half, and deep sleep occupying 60 to 66 per cent of the night against about 40 per cent beforehand, per Yahoo News. Less tidily, he came back short-sighted, a side effect he described in a later interview with WUSF.

Then came the eye-catching stuff. Dituri and his research team told the Jerusalem Post that his telomeres, the caps on the ends of chromosomes that usually fray with age, had come back 20 per cent longer, and that his circulating stem cells had multiplied roughly tenfold. He has since put his biological age at 34, down from 44.

Those numbers deserve a hard squint anyway. Dituri and his co-authors wrote the findings up as “The final frontier: what can we learn from surviving 100 days under the sea?” in the Aspetar Sports Medicine Journal, a paper confirmed on his university’s faculty page. Publication does not fix the underlying design: one man, measuring himself, with no control group or second subject to compare against. Dituri also runs a hyperbaric clinic built on his existing hypothesis that pressure heals brain injury, reason enough to take his own biomarkers with salt. A sample size of one is a story, not a finding, journal or not.

Somebody has since gone longer

Rüdiger Koch spent his 120 days in a Panama SeaPod with a bed, a toilet, an exercise bike and, tucked away for reading, a copy of Jules Verne’s novel about a man who never wanted to surface either, Inspenet noted. By January 2025, the German aerospace engineer had beaten Dituri’s mark by 20 days, a stretch Guinness World Records now lists as the longest stay in a fixed underwater habitat.

That pod was linked to a chamber above the waves by a tube with a spiral staircase, but the traffic ran mostly one way: food, visitors and a doctor came down to him. Cameras watched around the clock to confirm he never left, and Guinness credits him with the same unbroken exposure Dituri had, just five metres deeper and 20 days on top.

Which leaves the half inch as the one number nobody has followed up. Koch’s mission produced a new record and plenty of footage, but no public account of what his own spine did over those 120 days. The day count can be beaten by anyone with a deeper pod and more time submerged. Whether the height loss is a real, repeatable effect of sustained hyperbaric living remains one man’s data point, unchecked by the only other person who has stayed under that long.