Haenyeo Diving Physiology: What the Research Actually Shows

The average haenyeo working the coastal waters of Jeju Island today is around 70 years old, dives without scuba gear roughly 90 to 130 times per session, and does this several days a week in seawater that runs 10-13°C for a large part of the year. That is not a folkloric detail. It is the measured field data from a 2016 physiological study of nine working divers {Lee et al., 2016} {Industrial Health}, and it establishes the actual scale of what needs explaining: a population of elderly women performing sustained, repetitive, cold-water apnea diving as manual labor into their seventh, eighth, and occasionally ninth decade. The scientific literature on haenyeo is real, recent, and more specific than most popular coverage suggests — but it also documents a narrower and more qualified set of findings than the "secret to long life" framing implies.

• TRAINING EFFECTHaenyeo show a larger heart-rate drop during simulated diving than non-diving Jeju women (18.8 bpm vs. 12.6 bpm)
• GENETIC VARIANTA blood-pressure-lowering variant appears in about a third of Jeju residents, versus roughly 7% on the mainland
• BONE DENSITYLifetime free-divers show measurable differences in spinal bone mineral density versus non-diving peers
• COLD TOLERANCEOlder haenyeo retain superior extremity cold tolerance versus non-diving women of the same age
• KIDNEY RISKChronic kidney disease prevalence is measurably higher in breath-hold divers than in matched non-divers
• DIVE PROFILEReal-world dives are shallow (under 1m average) and short (about 11 seconds), unlike the deep dives of other diving populations

What Field Recordings of Diving Bradycardia Actually Show

Diving bradycardia — the drop in heart rate that occurs when the face contacts cold water, mediated by the trigeminal nerve and vagal outflow to the heart — is a well-established mammalian reflex, and it has been measured directly in working haenyeo. The 2016 field study fitted heart-rate monitors on nine active divers, aged 56 to 83, during a full working session in the sea and recorded a 20% average heart-rate reduction at the bottom of a dive compared to surface-swimming heart rate between dives {Lee et al., 2016} {Industrial Health}. That is a smaller reduction than the roughly 30% previously reported in younger haenyeo, and the study's authors interpreted the difference as evidence that older divers self-regulate their workload — shorter dives, fewer dives per hour, more rest — rather than pushing their cardiovascular systems as hard as they did decades earlier.

A more recent and considerably larger genetic-and-physiological study from Seoul National University researchers, comparing 30 haenyeo, 30 non-diving Jeju women, and 31 non-diving Seoul women, quantified the training effect directly: under a standardized simulated-diving protocol (face immersion in cold water), haenyeo heart rates dropped by an average of 18.8 beats per minute, compared to 12.6 bpm in non-diving Jeju women of similar age {Aguilar-Gómez et al., 2025} {Cell Reports}. Because both groups share the same Jeju genetic background but differ in diving history, this comparison is one of the cleaner pieces of evidence that a substantial part of the bradycardia response is trainable — acquired through decades of repeated apnea exposure — rather than purely innate.

The complication is that a 2025 field study using wearable sensors during actual open-water diving sessions found something different from the simulated-dive protocols: haenyeo did not show the overt, dramatic cardiovascular depression classically associated with elite mammalian diving, and instead showed elevated heart rates with only mild reductions in brain and muscle oxygenation during real dives {McKnight et al., 2025} {Current Biology}. The explanation the authors propose is methodological and behavioral rather than contradictory — haenyeo dives are shallow (averaging under a meter, some to about 4.75 meters) and short (roughly 11 seconds, with brief recovery intervals of under 10 seconds), a dive profile built around volume and repetition rather than depth and duration. A strong bradycardic dive response, useful for a single deep, long dive, may be less advantageous — or simply not triggered as strongly — across dozens of very short, shallow dives performed back-to-back for hours. The honest summary is that laboratory-simulated diving reliably elicits bradycardia in haenyeo, more so than in non-divers, while direct field measurement of their actual working dive pattern shows a milder and physiologically distinct response. Both findings are legitimate; they describe different things.

The 2025 Genetic Study: What Is Actually Jeju-Specific

The most methodologically important recent haenyeo research is the genetic association study published in Cell Reports in 2025, because it is the first to directly test whether Jeju's population carries genetic variants plausibly linked to diving, independent of training {Aguilar-Gómez et al., 2025} {Cell Reports}. Using genome sequencing and selection-scan analysis across the three-group comparison described above, the researchers identified a variant associated with lower diastolic blood pressure that is present in roughly a third of the Jeju sample but only about 7% of the mainland Seoul sample — a frequency difference large enough to suggest local selection rather than chance. The proposed adaptive logic is that lower resting diastolic pressure could offset the blood-pressure spikes induced by cold-water immersion and repeated apnea, a benefit plausible for pregnant divers specifically, since haenyeo have historically continued diving through pregnancy. The same study identified a second variant, in a gene previously linked to cold-water tolerance, at elevated frequency in the Jeju population, consistent with reduced susceptibility to hypothermia during prolonged cold-water exposure.

These are population-frequency associations from a single study with a modest sample size (91 women total across three groups), not a fully replicated, mechanistically confirmed causal pathway — a distinction the underlying paper itself is careful about, and one worth preserving here rather than overstating. What the study does establish credibly is that Jeju Island's population carries a distinct genetic signature relative to mainland Korea at these specific loci, and that the direction of the effect (lower blood pressure, better cold tolerance) is plausibly relevant to diving, even though — because non-diving Jeju women carry these variants too — the genetic component appears to be a population-level trait of Jeju ancestry generally, not something unique to women who became haenyeo specifically. The bradycardia advantage, by contrast, tracked with diving history rather than Jeju ancestry alone. The clean way to state it: Jeju islanders carry a shared genetic background that may confer some cardiovascular and thermal advantage for cold-water work; becoming a haenyeo and diving for decades adds a separate, trainable physiological adaptation on top of that shared background.

Haenyeo Are Not the Bajau: Two Different Populations, Two Different Genetic Stories

The best-known genetic diving-adaptation study in the scientific literature is not about haenyeo at all. In 2018, a Cell paper by Melissa Ilardo and colleagues documented genetic adaptations to breath-hold diving in the Bajau, a "Sea Nomad" population of Southeast Asia, finding that natural selection on variants near the gene PDE10A was associated with significantly larger spleens in the Bajau compared to a neighboring non-diving population — a larger spleen providing a bigger reservoir of oxygenated red blood cells that can be released during a dive — along with selection on a separate gene, BDKRB2, connected to the human diving reflex {Ilardo et al., 2018} {Cell}. That paper is frequently cited in general-audience coverage of "diving genetics" and is sometimes folded indiscriminately into discussions of haenyeo, but the two populations are genetically, geographically, and behaviorally distinct. The Bajau are a Southeast Asian population practicing generations of deep, breath-held spearfishing dives, and their documented adaptation (spleen enlargement via PDE10A) has not been reported in haenyeo. The Jeju genetic findings — the diastolic blood pressure variant and the cold-tolerance variant identified by Aguilar-Gómez and colleagues — are a separate, more recent, and much more preliminary body of evidence, discovered in a different gene set, in a different ethnic population, tied to a different dive profile (shallow and repetitive rather than deep and singular). Notably, the 2025 Current Biology field study on haenyeo diving behavior lists Ilardo as a co-author, reflecting direct scientific continuity between the two research programs — but continuity of researcher is not equivalence of finding. Treating the Bajau spleen result as if it were established haenyeo biology would misrepresent both papers.

Bone Density, Kidney Function, and the Documented Costs of a Lifetime of Diving

Load-bearing, high-frequency underwater work leaves a measurable skeletal signature. A 2018 Journal of Korean Medical Science study compared bone mineral density and rates of osteoporotic vertebral fracture in 30 lifetime free-diving haenyeo (mean age 72.1) against 33 non-diving women of similar age (mean age 72.7), finding differences in spinal bone density between the groups and examining how those differences related to vertebral fracture status {Seo et al., 2018} {J Korean Med Sci}. This is frequently summarized in popular coverage as "diving prevents osteoporosis," which overstates a single cross-sectional comparison in a modest sample; what the study actually supports is that decades of repetitive resistance loading from swimming, diving, and carrying loaded nets and buckets is associated with detectable differences in bone outcomes in this specific cohort, a finding broadly consistent with the well-established principle that mechanical loading preserves bone density in aging women, rather than evidence of a haenyeo-specific biological mechanism.

The cardiovascular training effect on diving bradycardia (18.8 bpm vs. 12.6 bpm) documented by the 2025 Cell Reports study is itself a marker of superior autonomic conditioning relative to age-matched peers, consistent with decades of repeated apnea functioning as a form of interval-style cardiovascular training. Separately, a Journal of Physiological Anthropology study from Seoul National University researchers found that older haenyeo retain superior local cold tolerance in their extremities compared to non-diving women of the same age, along with evidence of "cross-adaptation" — greater heat tolerance and altered warm-perception thresholds — even decades after haenyeo largely abandoned traditional cotton diving suits for wetsuits in the early 1980s {Lee, Park & Kim, 2017} {J Physiol Anthropol}.

Against these documented benefits sits a documented cost that is less frequently reported. A propensity-score-matched study of 715 breath-hold divers and matched non-divers, drawn from a larger sample of nearly 2,000 divers and over 3,400 non-divers, found chronic kidney disease prevalence significantly higher in breath-hold divers than in non-divers (12.6% versus 8.0%), with breath-hold diving remaining an independent risk factor after adjusting for other variables {Oh et al., 2017} {BMC Nephrology}. The proposed mechanism is chronic intermittent hypoxia from repeated apnea, structurally similar to the hypoxic stress implicated in kidney and cardiovascular strain from obstructive sleep apnea. A qualitative study of haenyeo health behavior adds a further complicating layer: divers reported managing chronic joint pain, hearing damage, and headaches largely through self-directed, sometimes excessive use of over-the-counter and prescription medication, often without full understanding of drug interactions, alongside a self-described ethos of "listening to the body, controlling greed, and adjusting work for safe diving" {Kim & Kim, 2018} {Qual Health Res}. A lifetime of apnea diving in cold water, in other words, produces a documented mixed physiological ledger: better cardiovascular training response and probable bone density benefits, set against elevated chronic kidney disease risk and joint and hearing damage requiring ongoing self-management.

What Cohort Data Does — and Does Not — Say About Haenyeo Longevity

The claim that haenyeo enjoy exceptional longevity compared to other Korean women is common in media coverage of Jeju, but it does not rest on a specific mortality or life-expectancy cohort study isolating diving as the causal variable. The peer-reviewed literature summarized above documents physiological differences — cardiovascular training response, bone density, cold tolerance, kidney disease risk — between haenyeo and non-diving comparison groups, but none of these studies track long-term mortality or life expectancy as an outcome. Jeju-wide health statistics, such as age-standardized stroke mortality figures, describe the general island population rather than the haenyeo subgroup specifically, and even those island-level figures require caution: differences of this kind between regions are influenced by numerous confounders (rural healthcare access, diet, smoking rates, baseline demographics) that a raw regional comparison cannot disentangle, and no rigorous study in the literature searched here isolates a haenyeo-specific mortality advantage from these broader regional patterns.

What is verifiable is a demographic fact working in the opposite direction from a "secret longevity population" narrative: the haenyeo population itself has collapsed, from roughly 14,000 registered divers in 1970 to around 4,000 by 2015, with the remaining divers averaging roughly 70 to 75 years old and very few young women entering the occupation {Lee, Park & Kim, 2017} {J Physiol Anthropol}. The visible image of vigorous 70- and 80-year-old divers reflects survivorship within a vanishing occupational cohort rather than proof that diving itself extends the lifespan of everyone who takes it up. The scientifically defensible claim is narrower than "haenyeo live exceptionally long": elderly women who have dived for decades show specific, measurable markers of cardiovascular and skeletal resilience relative to non-diving peers of the same age, alongside specific, measurable health costs, and the honest state of the evidence is that nobody has yet published the cohort mortality study that would confirm or refute a net longevity effect either way.

Separating Documented Physiology From Folk Narrative

The haenyeo research base that exists today — the 2016 and 2025 bradycardia field studies, the 2025 genetic association study, the 2018 bone density comparison, the 2017 cold-tolerance and kidney-function studies — is unusually rich for a population this small, and it supports a genuinely interesting physiological story: repeated cold-water apnea diving, sustained across decades, produces a measurable and partly trainable cardiovascular adaptation, occurs against a Jeju-specific genetic background that may independently favor lower blood pressure and cold tolerance, and correlates with distinct skeletal and renal outcomes in both directions. What the evidence does not support is the leap frequently made in popular retellings — that haenyeo demonstrate an exceptional, quantified longevity advantage, or that the Bajau's spleen-based genetic adaptation is somehow the same phenomenon documented in Jeju's divers. The more accurate and, frankly, more scientifically interesting picture is of two independently evolved responses to breath-hold diving in two unrelated human populations, and a single, aging Korean cohort whose fitness markers are real, whose health costs are also real, and whose ultimate effect on lifespan remains, as of this writing, an open empirical question rather than a settled one.

Robert Tanaka is the Senior Health Columnist at HealthKoLab. He holds a Master's in Gerontology from USC and has studied centenarian populations across Asia and the Blue Zones.