A group of women on South Korea’s largest island, Jeju, follow a unique tradition to provide food for themselves: They dive to depths of about 33 feet (10 meters) without using any special equipment. Now, a new study shows that these women carry special genes that South Koreans living on the mainland do not have. These genes may be linked to the women’s ability to withstand cold water and lower their blood pressure while diving.
Jeju Haenyeo — which translates as “women of the sea” — begin diving for seafood at around age 15, collecting abalone, sea urchins, and octopus. Members of the group collect fish for up to seven hours a day for about 90 days a year, according to UNESCO. They continue to do so into their 80s, even without a break during pregnancy, the scientists wrote in a study published May 2, 2025, in the journal Cell Reports.
Jeju Island’s female divers have been freediving for generations to obtain seafood. Melissa Ilardo
Ilardo previously studied another population of people who free dive for seafood: the Bajau, or “sea nomads,” of Indonesia. The difference is that the tropical island of Indonesia has warm water — about 80 degrees Fahrenheit (26.7 degrees Celsius) — while the water off Jeju Island can drop below 55 degrees Fahrenheit (12.8 °C). That’s hot enough to cause hypothermia. But the Jeju haenyeo are capable of diving in any temperature,” descending to depths of up to 10 meters (33 feet), typically for about 30 seconds at a time, according to the paper.
To explore the secrets of this group’s cold-water tolerance and endurance, Ilardo, the study’s author, and her team compared the genetics of 30 Jeju Island haenyeo with those of 30 non-divers from Jeju Island and 31 women from mainland South Korea.
Both the haenyeo and non-divers from Jeju had the same genetic makeup, which was markedly different from their mainland counterparts. This is likely because those living on the island shared close common ancestors, the researchers suggested.
Compared with mainlanders, Jeju Islanders were much more likely to carry a particular variant of the sarcoglycan zeta gene, a protein associated with cold sensitivity. The protein is found in smooth muscles that mediate involuntary movements, such as those involved in blood circulation. Studies have shown that it affects the pain of cold that can be felt when immersing a hand in icy water. Ilardo speculated that the variation in this gene could help explain the cold-water tolerance of free divers.
About a third of the women from Jeju Island — both divers and nondivers — carried a variant of the gene that codes for a protein called the Fcγ IIA receptor. By comparison, only 7% of women from the mainland carried the variant.
The data suggest that the protein helps regulate how muscles in the blood vessel wall respond to inflammation. If the variant helps limit inflammatory effects in blood vessels, the scientists speculated, it could lower diastolic blood pressure. (Blood pressure is typically measured by the ratio of systolic blood pressure, which measures the pressure in the arteries during heartbeats, to diastolic blood pressure, the pressure between heartbeats.)
Jeju’s Haeneyo continue to actively practice diving even at 80 and during pregnancy. Melissa Ilardo
The researchers explored this idea using simulated diving. They asked each participant to hold their breath while submerging their face in a bowl of cold water, which triggers the dive reflex. “Your body responds as if you’re diving, and that’s because the nerve that actually triggers the dive response is in your face,” Ilardo said. This reflex prompts the body to conserve oxygen by slowing the heart rate and constricting blood vessels, helping to ensure vital organs have enough blood flow, she added.
Overall, the Jeju participants had higher overall blood pressure than the mainland participants, and during the simulated dive, both groups experienced higher diastolic blood pressure than their baseline values. However, the researchers found that having the Fcγ IIA receptor gene variant was associated with significantly lower diastolic blood pressure in the Jeju participants during the dive.
This gene variant may help protect Jeju haenyeo from complications associated with diving-induced hypertension, or high blood pressure, which can be particularly harmful during pregnancy, the team suggested. However, these hypotheses have yet to be confirmed.
“The frequency of both genetic variants is the same in all Jeju Islanders,” Ilardo said. “Basically, it looks like all Jeju Islanders are equally likely to be descended from divers. Or, in other words, you’re either an active diver or the descendant of a diver.”
Tatum Simonson, a geneticist and physiologist at the University of California, San Diego, who was not involved in the study, says that linking the haenyeo’s physiology to their genetics is really valuable for understanding how people respond to hypoxia, or low oxygen levels. Simonson studies the genetics and physiology of people living at high altitudes, where atmospheric oxygen levels are lower than at sea level.
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“It’s possible that some of the same genetic variants are found in other groups,” she said, “and so this could be important in terms of studying how people respond to hypoxia-induced stress.”
Various medical conditions, including heart and lung disease, can also put the body into a hypoxic state, Simonson added. Broadly studying the genetic basis of how the body adapts to low-oxygen situations could potentially help scientists understand how the body responds to these disease states.
Some of the differences seen between divers and non-divers may be due to training rather than genetics, Ilardo added. In addition to the divers’ blood pressure drop, diving also affected their heart rates. One diver’s heart rate dropped more than 40 beats per minute in just 15 seconds during a dive — an effect not seen in other, non-diving populations.
This ability appears to be the result of a lifetime of training rather than genetics. Analysis revealed no specific gene associated with the ability, and what’s more, the Jeju divers and non-divers showed significant differences despite having much of the same genetic makeup.
Kara Ocobock, a biologist and anthropologist at the University of Notre Dame, told Live Science that our bodies respond to environmental extremes either through evolutionary adaptation, which happens over generations, or through acclimation, which happens over a lifetime.
“Even if you have a group of people who have been doing this diving for generations over a long period of time, you’ll see individual differences in how each person responds,” said Okobock, who was not involved in the new work. She studies how reindeer herders in Finland cope with cold temperatures.
Understanding how different populations adapt and acclimate to extreme conditions could potentially help identify strategies to help people cope with conditions that could be caused by climate change, Ocobock said. “That’s the kind of work we really need to do.”
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