“It’s like they have a superpower”: Genetic analysis of all-women extreme divers finds changes linked to blood pressure, cold tolerance

A new analysis of a group of all-women extreme divers off the coast of Korea has uncovered genetic differences that could help them survive the intense physiological stresses of free-diving—and could ultimately lead to better treatments for blood pressure disorders.

The results are published in Cell Reports.

The researchers worked with the Haenyeo: women who have spent their whole lives diving in the waters off Jeju Island, 50 miles south of mainland South Korea. They free-dive up to 60 feet below the surface to harvest seaweed, abalone, and other food items from the seafloor, spending hours a day in the water all year round. For hundreds of years, Haenyeo diving was a staple of Jeju’s economy and culture, although the practice is now waning. Today, most divers are in their 60s and 70s.

“They’re absolutely extraordinary women,” says Melissa Ilardo, PhD, assistant professor of biomedical informatics at University of Utah Health and the senior author on the study. “Every day, they head out and get in the water, and that’s where they work all day. I saw women over 80 diving off a boat before it even stopped moving.”

To figure out if the Haenyeo’s diving abilities are aided by differences in genetics, the researchers measured physiological variables related to diving ability, such as blood pressure and heart rate. They then sequenced participants’ DNA—and found two changes related to diving physiology that could give the Haenyeo advantages underwater.

Adapting to a high-pressure environment

Haenyeo divers are more than four times more likely than mainland Koreans to have a genetic change associated with lower blood pressure while diving. The researchers believe this difference could keep divers and their unborn children safe when diving during pregnancy.

Breath-hold diving not only limits the body’s oxygen supply but also raises divers’ blood pressure during a dive, the researchers say. Holding one’s breath in other contexts, such as sleep apnea, is associated with pregnancy-related blood pressure disorders, although it’s unknown whether diving causes the same effect.

The researchers speculate that if the genetic change helps lower blood pressure, it could be especially vital for the Haenyeo. These women dive throughout pregnancy and must avoid blood pressure conditions such as preeclampsia, which can be fatal. “This is not something that every human or every woman is able to do,” says Diana Aguilar-Gómez, PhD, postdoctoral researcher in evolutionary biology at University of California, Los Angeles, and the first author on the study. “It’s kind of like they have a superpower.”

Cold comfort

A second genetic difference is related to pain tolerance—specifically, cold-based pain. Air temperatures off Jeju Island drop to around freezing in the winter, but the Haenyeo don’t stop diving. “I asked them once if they would stop diving if it got cold enough,” Ilardo says. “They said that as long as the wind alarm doesn’t go off, they’ll still get in the water.” She clarifies, “The wind alarm is to keep them from blowing out to sea.”

The team didn’t measure individuals’ cold tolerance, so they can’t say whether the change they see may be important for the Haenyeo’s ability to dive year-round. But they plan to investigate the difference further in future work.

The genetic differences that could boost diving ability are found throughout the population of Jeju Island. But much of what makes the Haenyeo women special comes from a lifetime of practice. Researchers have long known that when anyone dives—trained or untrained, Haenyeo or not—their heart rate reflexively drops to conserve oxygen for longer. For an average untrained person from Jeju Island, heartbeat slows down by about 20 beats per minute over the course of a simulated dive. For Haenyeo with a lifetime of diving experience, heart rate drops by up to twice that.

Advancing health for all

The researchers hope that their discovery of a genetic difference linked to blood pressure will ultimately advance care for health conditions, like stroke, that are related to high blood pressure.

Intriguingly, Jeju Island has one of the lowest rates of stroke mortality in Korea, raising the possibility that the genetic change could help protect against stroke, Ilardo says. “If there’s something about it that actually reduces the risk of stroke mortality, then we could help people everywhere by understanding what’s special about these women.”

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This research is published in Cell Reports as “Genetic and Training Adaptations in the Haenyeo Divers of Jeju, Korea.”

This research was supported by the Office of Naval Research (N00014-20-1-2556), the National Institute of Health (NIGMS R35GM153400, NHGRI R00HG011658), the National Science Foundation (Graduate Research Fellowship 2146752), the UC MEXUS-CONACYT Doctoral Fellowship, and the Fulbright-García Robles.

Content is solely the responsibility of the authors and does not necessarily represent the official views of the National Institutes of Health.