On June 9, 2023, biomedical engineer Joseph Dituri slowly emerged from the ocean off Key Largo, Florida, after living underwater for a record-breaking 100 days.

He ate, slept, pee-ed, and even taught university classes 6.7 meters below the waves in a 9.3 square meter living space. And intrepid ocean dwellers, or aquanauts, have been having a go at underwater life since the 1960s.

But it kinda makes you wonder: What does living underwater for months do to the human body? And how long could we ultimately stay down there? [♪ INTRO] Thanks to Brilliant for supporting this SciShow video! As a SciShow viewer, you can keep building your STEM skills with a 30 day free trial and 20% off an annual premium subscription at Brilliant.org/SciShow.

Crushing a world record might be a nice perk for testing the limits of underwater living. But there’s some valuable science in those tests, too. For one thing, the cramped quarters are pretty similar to what astronauts have to deal with in space.

So living underwater is a neat way to figure out how we might fare on, say, a trip to Mars. But there’s plenty to explore down on Earth, too. About 75% of the ocean floor is still uncharted, so an underwater habitat is a great spot to set up camp and conduct research.

Take the Aquarius research base off the coast of Key Largo. Sitting 19 meters under the sea, this 37 square meter lab houses scientists and astronauts-in-training for up to 3 weeks at a time. But most visits are shorter.

In two recent studies for NASA, aquanauts spent between 9 and 10 days at Aquarius and tracked how they fared both physically and psychologically. In terms of physical effects, the aquanauts overall had lower blood pressure, heart rate, and breathing rate compared to up top. That might be because the air they were breathing was at a much higher pressure than they’re used to.

The higher pressure probably makes it more exhausting to move your lungs, so it makes sense you wouldn’t want to breathe as often. But it could also manipulate certain hormones that control how fast and how much the heart pumps. In addition to those changes, the aquanauts lost weight, an average of 1.3 kilograms!

Researchers aren’t exactly sure why, but it probably wasn’t due to a lack of appetite. According to some other interviews, other aquanauts have reported feeling ravenous down there. That might be thanks to the thicker air pulling heat away from their bodies and putting their metabolisms on high alert to keep them warm.

On the psychological side, aside from being kinda stressed out before and during the mission, the aquanauts’ mood stayed pretty positive throughout the experience. Unlike other deep-sea missions, these aquanauts could keep in touch with loved ones and even binge their favorite shows on Netflix. So maybe a short stint with access to television isn’t really that tough on our bodies or minds.

But other underwater missions have gone for longer, and a lot deeper too. In 1965, teams of 10 aquanauts spent 15 days each 62 meters beneath the waves of La Jolla, California as part of the United States Navy’s SEALAB II mission. The SEALAB II capsule was only about the size of a small apartment and wasn’t exactly comfortable.

And when you force 10 people to share that space? It’s safe to say privacy was practically non-existent. But while the crew did rate themselves as being more worked up and scared when they were below the surface.

One review of the mission said that the crew, quote, “weathered the stresses very well”. In fact, most participants said they wished they could have spent more time there. Meanwhile, the most notable physical side effect was probably in the aquanauts’ voices.

SEALAB was so deep it wasn’t possible to pump in pressurized air from the surface like they do for Aquarius. You know, the classic 78% nitrogen, 21% oxygen stuff. So instead, the aquanauts inhaled a mix of 16% nitrogen, 4% oxygen, and 78% helium!?

Which made for some pretty hilarious, but also really hard to understand, conversations. But there were some other physical side effects that were a little more serious. In order for the aquanauts to easily go for dives outside, part of the lab was open to the water.

And that made things super humid. So most of the SEALAB team ended up with ear infections or skin rashes. Still, SEALAB’s longest mission wasn’t even a month long.

So what might happen to a human that stays longer? Well in 1969, the Tektite I team ended their 60-day mission– 60 days! It was the first of roughly a dozen missions in the Tektite habitat, located 15 meters below the surface of Great Lameshur Bay in the U.

S. Virgin Islands. And according to a 400-page-long report, the mission was surprisingly uneventful.

Measurements made before, during, and after the mission showed there weren’t any notable changes in their blood chemistry, blood cell count, or immune systems. The only thing the aquanauts really noticed was they found it harder to breathe because the air was denser than normal. This time the pressurized air wasn’t chock full of helium, but it did have higher nitrogen and lower oxygen percentages than you’d find on the surface.

But those numbers are actually a concern for extended stays underwater. Aquanauts and even recreational scuba divers can go a little loopy from breathing in too much nitrogen. The technical term for this is nitrogen narcosis.

No one in Tektite reported suffering from narcosis, but some participants in land-based experiments that were designed to simulate underwater conditions have. So the specific kind and pressure of the air aquanauts are breathing is something to keep in mind on future missions, especially ones that last for several weeks. But what does Dituri’s whopping 100 day stay bring to the table?

Is there anything else that future aquanauts will have to worry about? Well, his observations still need to be written up as scientific studies and peer reviewed, so take this with a grain of sea salt. But he’s already discussed some side effects with reporters, like shrinking by about half an inch, and temporarily becoming super nearsighted.

That’s because his eyes stopped having to focus on things any further away than the walls of his habitat. But lucky for him, his vision went back to normal after a couple of weeks. Dituri has also reported improvements in his cholesterol, sleep, and levels of inflammation.

So maybe it really is better down where it’s wetter. As for psychological effects, Dituri felt a little bummed that he missed milestones like his daughter’s graduation. But he had enough people visit him at the lodge, as well as regular social interactions online, that he managed to persevere.

So we know a human can stand 100 days underwater both physically and psychologically, assuming they have a decent amount of contact with the outside world. But could humans stay a year underwater? multiple years? Decades?

We simply don’t know. But at least one expert says that whatever that length of time is, it’s not indefinitely. That’s because aquanauts are breathing in denser air, meaning they’re breathing in more oxygen molecules, which could eventually damage their circulation systems.

Some land-based studies using hyperbaric oxygen chambers say that our bodies might be able to adapt. But the participants in those studies only stayed in that environment for a few days. Not 100 days.

But we might get a clearer picture soon! Dituri is set to present details of his journey at a conference later this month. Maybe he’ll inspire other scientists to keep pushing the limit.

I mean who wouldn’t want to break a record? And look at those astronauts up there. One of them just set a U.

S. record of 371 consecutive days in space. You aquanauts gotta catch up! If you’re the kind of person who loves breaking records and winning competitions, you’re probably just who Brilliant had in mind when they created their course in Contest Math.

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Thanks to Brilliant for supporting this SciShow video! [♪ OUTRO]