A new study has focused on the physiology of renowned female free divers from Jeju Island in South Korea, known as “sea women.”
These daring individuals, following an ancient tradition, provide for their families by diving to depths of 10 meters without any special equipment. The “sea women” begin diving for sea urchins, shellfish, and octopuses at the age of 15. According to UNESCO, these women spend about 7 hours a day gathering seafood in cold waters for approximately 90 days each year. Remarkably, they continue to dive until the age of 80, even during pregnancy.
Researchers believe that these women possess unique genes not found in their mainland counterparts. These genes may be linked to their ability to withstand cold water and lower blood pressure while diving.
What Did the Researchers Discover?
Melissa Ilardo, the lead author of the study from the University of Utah (USA), noted in an interview with Live Science, “It’s not just that they do this at an older age, but how athletically they do it; it’s mind-blowing.”
Previously, Ilardo studied another population of people who engage in free diving for seafood: the Bajau, or “sea nomads,” in Indonesia. The difference is that in tropical Indonesia, the water is warm—around 26.7 °C—while the waters around Jeju Island can drop below 12.8 °C, which is cold enough to cause hypothermia.
According to the scientist, South Korean women dive into the water at any temperature, typically for 30 seconds at a time.
To uncover the secret behind these women’s cold water tolerance and endurance, Ilardo’s team compared the genetics of 30 women from Jeju Island who dive for seafood, 30 island women who do not dive, and 31 women from mainland South Korea.
It turned out that both the “sea women” and the non-diving island women had the same genetic makeup, which was significantly different from that of the participants from the mainland. This is likely due to the islanders sharing common ancestors.
Compared to mainland residents, island women were significantly more likely to carry a specific variant of the gene encoding the protein called sarcoglycan zeta, which is associated with cold sensitivity. This protein is found in smooth muscles that facilitate involuntary movements, such as those involved in circulation. Researchers suggest that a change in this gene may explain the cold water tolerance of free divers.
About one-third of the women from Jeju Island—both divers and non-divers—carried a variant of the gene that encodes a protein known as the Fcγ IIA receptor. In contrast, only 7 percent of women from the mainland carried this variant.
The study data indicate that this protein helps regulate the muscle response in blood vessel walls to inflammation. If this variant helps mitigate inflammatory effects in blood vessels, it may also lower diastolic blood pressure, the scientists proposed.
The researchers explored this idea through a simulated dive. They asked each participant to hold their breath while submerging their face in a bowl of cold water. The immersion effect triggered the body to conserve oxygen by slowing the heart rate, constricting blood vessels, and ensuring vital organs receive adequate blood supply.
Overall, participants from Jeju Island had higher blood pressure than those from the mainland. During the immersion simulation, both groups exhibited elevated diastolic blood pressure. However, researchers found that the presence of the Fcγ IIA receptor gene variant was associated with significantly lower diastolic blood pressure in the “sea women” during immersion.
This gene variant likely helps protect the divers from complications related to hypertension caused by diving or high blood pressure, which can be particularly harmful during pregnancy, the team believes. However, these hypotheses still need to be confirmed.
The study’s findings were published in the journal Cell Reports.