Japan’s Famous Deep-Sea Divers Give Clues to Better Vascular Health

By Gretchen Sanders in 40 Acres, Nov | Dec 2017 on November 1, 2017 at 8:00 am | No Comments

A woman bobs up and down in the cold Pacific Ocean surrounding Japan’s Shima peninsula. She remains on the surface just long enough to release a breath she’s held for nearly two minutes. Then, sucking in a large gulp of air, she plunges 30 feet back to the seabed, where she scours for shellfish, seaweed, and pearls. She will dive this way a hundred times before the sun sets. Later, she’ll sell her haul in a fish market. It’s a routine Japanese pearl divers, called ama, have practiced for nearly 2,000 years.

These mostly female free divers spend some four hours a day at sea, completing up to 150 dives each day. Vigorous as any pool workout or spin class, pearl diving doesn’t make the women thin. Ama divers, with their robust bodies, look more ready for an Arctic Ocean dip.

New research suggests that this ancient occupation, a dying way of life, yields health rewards that far outweigh the modest income it provides.

Hirofumi Tanaka, director of UT’s Cardiovascular Aging Research Laboratory, coauthored a study last year in the American Journal of Physiology—Regulatory, Integrative and Comparative Physiology that shows pearl divers have more flexible arteries due to their lifestyle. This finding is a vascular-health treasure buried in Japan’s long history of pearl harvesting.

The Shima peninsula, home to roughly 800 ama, is known for its beautiful coastline, seafood, and pearl cultivation. Through the ages, diving for saltwater pearls offered work and adventure to women living in the region’s coastal villages. Females proved better divers because they have more body fat for insulation against the biting cold. Many ama started out as teenagers and have stayed in the profession until very old age—some diving well into their 80s.

Today, only about 2,000 ama remain in Japan. Their average age is 65. A tradition that once passed from mother to daughter no longer attracts younger generations. With better-paying jobs available, who wants to face sharks, hypothermia, or decompression sickness?

But Tanaka points to some of the built-in medical benefits that come from repeated deep-sea diving. “We found that Japanese pearl divers have significantly less arterial stiffening compared to people the same age in the same villages,” he says.

Arteries carry oxygen-rich blood to organs; veins carry blood back to the heart. Healthy arteries have the elasticity of a rubber band, expanding with each heartbeat and contracting between them. Arteries naturally stiffen with age, but overly stiff arteries can lead to hypertension, stroke, and kidney disease. The ama have unintentionally reduced their risk for these conditions. But how?

Tanaka, who grew up in Tokyo, has focused much of his research on vascular function. He also harbors a special curiosity about how certain structures and mechanisms in the human body mimic those seen in wild animals. “Compare humans to diving mammals,” he says. “They both share the mammalian diving reflex.” If a pearl diver dips her head in cold water, her blood will rush to her heart and brain, and her heartbeat will drop to 40 beats per minute. The same thing happens to a seal. This reflex helps mammals conserve energy, so they can stay underwater longer in search of food—or pearls.

 

Sea-diving mammals have arterial adaptations that help them tolerate the physical demands of ocean life. Whales have an ascending aorta that is three to four times larger than their descending aorta, which enhances the elasticity of the artery and helps maintain blood flow when a whale’s heartbeat drops during a dive. Tanaka wondered if pearl divers had adapted similarly from years of diving. Had their arteries evolved to mimic in structure and function the arteries of a whale?

In the summer of 2015, Tanaka and two other scientists studied 115 pearl divers from Japanese villages Shima, Toba, and Chima. Most of the women were in their mid-60s and had decades of diving experience. Tanaka and his team measured arterial stiffness in each diver using a technique called pulse wave velocity. “The faster the pulse wave travels in the blood vessel, the stiffer the blood vessel,” Tanaka explains. A slower pulse wave equals a softer, more elastic artery.

Stacked up against 50 non-active residents from those same villages, the pearl divers exhibited significantly lower arterial stiffness and reduced arterial wave reflection. Surprisingly, they did not have superior lung function. This may result from how they exhale. After surfacing, pearl divers open their mouths only slightly, letting air out in a slow, low whistle. This maneuver helps to protect their lungs and prevents excessive hyperventilation, but it does not boost lung power.

While it’s not news that aerobic exercise reduces arterial stiffness, “this study adds to our understanding of the process,” says Austin cardiologist Craig Siegel, a Longhorn Aquatics Masters swimmer. Pearl divers, fit from a lifetime in the ocean, resemble Masters athletes, like Siegel, in that they exercise close to their maximum physical capacity.

Tanaka would have to do more research to know definitively whether it’s strenuous aerobic exercise or years of repeated deep diving—or both—that gives Japanese ama divers such healthy gems for arteries.

As the workday ends and the sea sweeps the ama to shore, they gather in huts around a fire. Sometimes they pray in its warmth. Sometimes they talk about the dearth of divers to replace them. Now, they can brag about their health.

Photos courtesy of the photo book Ama by Nina Poppe