U.S. Navy looks to South Korea's free-diving women for hypothermia remedy

The haenyeo population has been in decline for years and now most are now in their 70s. Photo courtesy of Jeju Tourism Organization
1 of 10 | The haenyeo population has been in decline for years and now most are now in their 70s. Photo courtesy of Jeju Tourism Organization

JEJU ISLAND, South Korea, Sept. 7 (UPI) -- As the once inaccessible Arctic grows as a region of military concern under the effects of global warming, the U.S. military is confronted with the problem of protecting its soldiers from the stresses of cold water and the threat of hypothermia. Researchers have turned to a peculiar place for potential answers: South Korean grandmothers who harvest seafood from the ocean floor.

Off the coast of South Korea's southern resort island of Jeju, about 280 miles south of the capital Seoul, these elderly women known as haenyeo dot the ocean as they dive year-round for abalone, turban shells, sea mustard and agar.


They've been free diving for generations, with the profession generally inherited from mother to daughter. It has also changed little over the years, with the main difference being the discarding of white cotton bathing suits in the early 1970s for the black rubber wetsuits they wear today.


Their numbers have been dropping for decades, with most now well into their 70s or older. But they live as icons of the island's culture and a symbol of the femininity and strength of its women who have been the breadwinners for their families upon a volcanic island where farming is limited and against a backdrop of political strife and oppression.

To Tae Seok Moon, an associate professor at Washington University in St. Louis, these women were the inspiration behind a research project that aims to combat hypothermia.

"This is probably the most craziest idea I ever imagined," he told UPI in an interview over Zoom.

Moon has been awarded a three-year grant worth more than $500,000 from the Office of Naval Research, which conducts science and technology programs for the U.S. Navy and Marine Corps, to study how the human microbiota, which are microorganisms that live on our skin and in our guts, may contribute to heat generation in cold environments, such as underwater.

His so-called crazy idea is to eventually engineer these microorganisms that maintain a symbiotic relationship with their host humans to generate heat when the environmental temperature drops.

"Basically, what we want to develop is a genetic circuit -- we call it a genetic circuit -- that is basically in the bacteria that allow microbes to increase heat production in response to temperature downshift," he said.


The microbes, he said, would also be able to reduce heat generation if exposed to a warm environment to maintain homeostasis of the human body.

The human body consists of 10 times as many microbial cells as human cells, and Moon said that for a healthy 154-pound adult, these cells could increase one's body temperature by 1 degree Celsius per hour.

Arctic divers

Sandra Chapman, program officer at the ONR, told UPI its interest in Moon's project has to do with Navy divers.

"Expanding future Naval operation in Arctic regions will place a greater demand for better thermal protection for our warfighters," she said in an email. "Therefore, ONR seeks a smart-technology approach that can sense and respond to changes in temperature exposures, and the microbiome represent a promising solution to serve as our bodies' own thermostat."

Global warming is reshaping the world, and the Arctic has grown as a region of military concern with countries jockeying not only for influence over newly melted trade routes and access to vast untapped reservoirs of natural resources but to protect their northern borders and national interests from adversaries.

The United States has been ramping up its presence in the region, as have Russia and China, and the various branches of the U.S. military have been announcing their strategic blueprints for the region, which despite having the smallest of the five oceans could potentially connect 75% of the world's population.


According to the U.S. Navy, it is also home to an estimated 30% of the world's undiscovered natural gas reserves, 13% of global conventional oil reserves and rare earth minerals valued at $1 trillion.

To optimize the capabilities of Navy divers in wartime demands a seamless transition between environments, Chapman said, a difficult task due to static technologies such as wetsuits, which cannot adapt to their environment and lose their thermal protection at depth and if ripped or torn.

"If we are able to use our resident microbiota to adapt to changing temperatures, we would be free from the current reliance on the different thermal protection needed for each different environment," she said.

Adapting to cold

Moon, an engineer of microbes, told UPI the haenyeo of his native South Korea were the inspiration behind the project because he wondered if their microbiota had adapted over generations to combat the cold water.

"Haenyeo is one strong example of who basically stand cold temperatures. So right now they have some nice wetsuits, and that kind of protects their body from the heat [loss], but think about 100 years ago and 200 years ago and then haenyeo is descended from those haenyeo," he said. "Normally, the kids become haenyeo and their kids become haenyeo, and that means genetically the haenyeo are strong people."


He mentioned the work of Melissa Ilardo, an adjunct faculty member at the University of Utah, who studied Indonesia's Bajau or Sea Nomads, finding that these divers have spleens 50% larger than their land-living counterparts. He wondered whether similar adaptations might be found in haenyeo.

Chapman said they have sponsored Ilardo through a grant to study the thermal resilience of haenyeo with two objectives: to investigate the genetics and physiology underlying previously identified adaptations; and to probe novel genetic and physiological adaptations.

"This is really just the start of many questions about this population, especially depending upon the results that we get" from these investigations, Ilardo told UPI in a video call from Salt Lake City. "No one has really looked at the genetics of the haenyeo before, so this is going to be a really unique look into their genetic history and from that, there will be many more questions that we can ask."

Illardo said the Navy is "very interested" in the island's indigenous divers due to their ability to work for up to eight hours a day in cold water -- water "much, much colder" than other indigenous divers are generally exposed to.

According to, Jeju's water temperature can drop to below 53 degrees F during the winter months.


"I don't personally know of any other population diving in waters as cold as the haenyeo," she said.

Navy divers have told her their greatest challenge is the cold.

"Given that that's kind of the number one obstacle to their ability to complete tasks underwater, more so than equipment, more so than gas mixes -- a lot of those things are really well dialed at this point -- but once they get cold to a certain point, they say they can't use their hands, they can't stay underwater any more, and so the haenyeo being able to stay in that cold water for so long was really exciting to everyone as a possibility to pursue," she said.

Genetic factors

Ilardo was in Jeju the Thanksgiving before the pandemic hit to conduct measurements and experiments with the haenyeo with plans to publish her findings by the year's end.

Without getting into specifics, she said at times the phenotypes of haenyeo, or their observable physical properties, appear similar to non-divers in Jeju, but then there's other instances where they look completely different.

This could be the result of a mixture of environmental and genetic factors that she said she will now "tease apart" to see which might be genetic and which might be the result of their environment.


Studies have shown that the haenyeo's ability to withstand cold water has diminished somewhat following the switch from cotton to rubber diving suits in the 1970s, with a study published in 2017 asserting that "their overall cold-adaptive traits have disappeared."

Ilardo said the decrease in their thermal tolerance makes sense but that produced by their genetic adaptation, if one exists, would still persist. That is a question that current data cannot answer.

"I think they've been doing it for so long and hypothermia is so dangerous and particularly if you were carrying a child -- I can't imagine the strain that would put on a fetus -- I would lean toward genetics," she said, "but I'll have an answer soon."

One reason why she is optimistic that a genetic signal within the haenyeo will be discovered is that they dive while pregnant.

"If you have some kind of adaptation that kind of buffers that strain then your child is more likely to survive to birth," she said.

The Haenyeo Museum, located near Jeju City, confirmed that haenyeo did dive while pregnant but the number who did may not be as many as the widely reported claim suggests.

In an email to UPI, the museum said only "a small percentage and not all haenyeo" dived while pregnant and the fact they did "is proof that Jeju women had a strong sense of responsibility" to take care of their family.


Disappearing profession

The issue the haenyeo seemingly present to researchers is that the profession's future is uncertain.

Once a prominent and financially important profession for the island, haenyeo have been decreasing for decades.

The museum said the government began collecting data on the haenyeo in 1965, with the 24,268 counted in 1966 being the highest on record, though prior to the 1960s, the number of divers would have been much higher.

At that time, more than 9,000 were between the ages of 15 and 20 while another 7,200 were 21 to 30 years old, it said.

Last year, there were 3,613 haenyeo remaining, 97.8% of whom were over age 50, according to the museum. Only four, it said, were younger than 30.

Illardo explained that the death of the profession does not mean that the future descendants of haenyeo will lose the ability to withstand cold water if that ability is derived from a genetic mutation.

"Like the Bajau who have this large spleen, if they're farming, it's not going to make it harder for them to survive," she said. "It adapted to diving but it's not harmful so they're going to have just as many children and they're going to survive just as long as anyone else or maybe even longer if it's advantageous in some other way. That won't decrease its frequency, but mixing with other cultures will."


What the military and researchers can learn from this population who test the limits of human physiology is what the limits of the human physiology really are.

"It's really through how it can be stretched and how it can be exceeded that we understand how it's working in the first place," she said.

Moon said his project right now is "completely fundamental" but that once the three-year investigation into the heat-generation mechanism has been completed, the Department of Defense may want to expand it further.

"Once this is successfully done, my future project will be visiting haenyeo and collecting some samples from skin," he said.

The end goal, he said, is to create something akin to a sunblock one smears on their skin or a pill one swallows containing the engineered microbiota that will generate heat when the user is exposed to a cold environment to prevent their body's temperature from dropping too low and ward off deadly hypothermia.

He said he may infuse it with the smell of Jeju's famed tangerines of green tea as a reminder from where his crazy idea first came from.

Asked if there was interest in studying the specific microbiome of the haenyeo, Chapman said no such project was currently supported by the Office of Naval Research but that it "may form an objective for future studies."


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