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A new study has focused on the physiology of renowned female free divers from Jeju Island in South Korea, known as “sea women.”
These women, following an ancient tradition, provide for their families by diving to depths of 10 meters without any special equipment. The “sea women” start diving for sea urchins, shellfish, and octopuses at about 15 years old. According to UNESCO, they spend roughly seven hours a day gathering seafood in cold waters for about 90 days each year. Remarkably, many continue diving into their 80s and even dive while pregnant.
Researchers believe these women carry gene variants not commonly found in mainland South Koreans. Those variants may be linked to their tolerance for cold water and lower blood pressure while diving.
What Did the Researchers Discover?
Melissa Ilardo, the lead author from the University of Utah, told Live Science, “It’s not just that they do this at an older age, but how athletically they do it; it’s mind-blowing.”
Ilardo previously studied another population of free divers who harvest seafood: the Bajau, or “sea nomads,” in Indonesia. The key difference is temperature—Indonesian waters are tropical, around 26.7 °C, while the waters around Jeju Island can drop below 12.8 °C, cold enough to cause hypothermia.
Ilardo said the Jeju divers enter the water at any temperature and typically hold their breath for about 30 seconds at a time.
To dig into the genetics behind the divers’ cold tolerance and endurance, Ilardo’s team compared the DNA of 30 Jeju women who dive for seafood, 30 island women who do not dive, and 31 women from mainland South Korea.
Both the divers and the non-diving island women had similar genetic profiles, which differed significantly from those of the mainland participants—likely reflecting shared ancestry among islanders.
Compared with mainland residents, island women were far more likely to carry a specific variant of the gene that encodes the protein sarcoglycan zeta, which is linked to cold sensitivity. That protein is found in smooth muscles that control involuntary movements, including those involved in circulation. The researchers suggest a change in this gene could help explain the free divers’ tolerance for cold water.
About one-third of Jeju women—both divers and non-divers—carried a variant of the gene that encodes the FcγIIa receptor protein. In contrast, only 7 percent of mainland women carried this variant.
The data suggest this receptor helps regulate how vascular smooth muscle responds to inflammation. If the variant reduces inflammatory effects in blood vessels, it could also lower diastolic blood pressure, the team proposed.
To test that idea, the researchers ran a simulated dive. Each participant held her breath while submerging her face in a bowl of cold water. The immersion triggered the body’s oxygen-conserving response: the heart rate slowed, blood vessels constricted, and blood was redirected to vital organs.
Overall, Jeju participants had higher baseline blood pressure than mainland participants. During the immersion test, both groups showed increased diastolic blood pressure. However, the presence of the FcγIIa receptor gene variant was associated with significantly lower diastolic pressure in the “sea women” during immersion.
The team suggests this gene variant may help protect divers from hypertension-related complications caused by diving or by high blood pressure during pregnancy. Those hypotheses still need confirmation.
The study’s findings were published in the journal Cell Reports.
