Can an intense belief that you're about to die actually kill you? Researchers are learning more about "voodoo death" and how it isn't limited to superstitious, foreign cultures.

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In 1977, the Centers for Disease Control and Prevention started receiving reports that otherwise healthy Southeast Asian men were dying mysteriously in their sleep, some with terrified expressions on their faces. Researchers, at a loss, called it SUNDS—Sudden Unexpected Nocturnal Death Syndrome. In particular, SUNDS disproportionately affected Hmong refugees from Laos. At the peak of the "epidemic" in 1981, Hmong men were dying from SUNDS at the same rate as American men in the same age group were dying from the five leading causes of natural death—combined.

“People didn’t know at all what was going on,” says University of California-San Francisco professor Shelley Adler, who was a graduate student studying medical anthropology at the time. But after interviewing 118 Hmong men and women about their experiences, her suspicions were confirmed. Many attributed the deaths to fatal attacks from dab tsog, an evil nighttime spirit in the traditional Hmong religion that crushes men at night. Their descriptions of dab tsog were similar to sleep paralysis, a disorder in which a person’s mind awakens while their body is still asleep or paralyzed; they often feel like they are being crushed and experience hallucinations.

But there were still unanswered questions. “Sleep paralysis alone is not fatal,” Adler says. “Sleep paralysis alone does not kill anyone. Why was it fatal for the Hmong?”

SCIENTISTS ARE JUST BEGINNING to understand how cultural beliefs can lead to psychological stress, illness, and even death. American physiologist Walter Cannon was one of the first people to write about the potentially fatal consequences of these intense beliefs. In 1942, reports were streaming in from around the world about “voodoo” death: South American Tupinamba men, condemned by medicine men, died of fright. Hausa people in Niger withered away after being told they were bewitched. Aboriginal tribesmen in Australia, upon seeing an enemy pointing a hexed bone at them, went into convulsions and passed away. “Voodoo” death, according to Cannon, was real: “It is a fatal power of the imagination working through unmitigated terror.”

Psychological stress—especially, in these cases, due to cultural beliefs—can be significant enough to cause major health issues.

Researchers today continue to find evidence of it. “I’d been thinking for a long, long time, how I would test this idea that fear makes a difference,” says David Phillips, a sociology professor at the University of California-San Diego. He learned from a student that many Chinese and Japanese people are superstitious about numbers, particularly the number four, which is considered unlucky because it sounds like the word for “death.” Phillips decided to crunch cardiac mortality figures for all Chinese and Japanese Americans who died from 1973 to 1998 on the fourth of each month. He found that cardiac deaths were seven percent higher than expected for Chinese and Japanese Americans on the fourth day of each month when compared to white Americans. That number rose to 13 percent for chronic heart disease deaths and was at its strongest, at 27 percent, in California, which accounts for almost half of the Chinese and Japanese deaths in the U.S.

After examining other plausible reasons for this phenomenon, Phillips’ paper concludes that “the only explanation consistent with the findings is that psychological stress linked to the number four elicits additional deaths among Chinese and Japanese patients.”

EVENTUALLY, SCIENTISTS BEGAN PIECING together parts of the SUNDS puzzle. In 1992, researchers identified a genetic mutation called the Brugada syndrome, which causes abnormal electrical impulses in the heart and could be linked to SUNDS and Sudden Infant Death Syndrome. An extensive survey and sleep study of Hmong in Wisconsin confirmed that they were six to seven times more likely to have sleep apnea, and 10 times more likely to report frequent sleep paralysis, than non-Hmong.

But the genetics didn’t paint a complete picture. SUNDS deaths peaked in 1981, the same year that the number of Southeast Asian refugees migrating to the U.S. was at its highest. Then the deaths gradually stopped. Plus, the Hmong that Adler interviewed had never heard of anyone dying from a dab tsog encounter in Laos.

“If it is a genetic disorder, why aren’t people still dying from it?” Adler asks. “Why was there that peak in deaths? Why did the death happen with greater frequency when folks were [in the U.S.] for little over a year?”

The answer, Adler believes, could lie in the very phenomenon that Phillips had observed in Chinese and Japanese deaths: Psychological stress—especially, in these cases, due to cultural beliefs—can be significant enough to cause major health issues.

Adler’s interviews with Hmong refugees revealed that many of them had undergone traumatic experiences in the Vietnam War and struggled to transition to life in the U.S. Two-thirds of Hmong surveyed in Wisconsin reported negative experiences from the war, and one-third reported chronic pain; the prevalence of depression, anxiety, and PTSD is high among Hmong and other Southeast Asian refugees. Without the support of tight-knit communities and traditional religious structures and systems, many feared that the protective spirits of their ancestors were unable to defend them against dab tsog. Fear of of dab tsog caused so much stress among Hmong men that some would set their alarm clocks to ring every 20 to 30 minutes to avoid deep sleep.

“[The genetic component] seemed to be compounded by refugee stress, a period of shock,” Adler says. The overwhelming stress, in effect, could have “triggered” Brugada to unmask itself.

FOR A LONG TIME, research connecting psychological stress to adverse health consequences was anecdotal. “The more we studied it, the more we realized that power of suggestion is so important,” Adler says. Now, studies that use fMRI technology and measure hormones in our saliva and urine can illustrate how mental trauma, stress, or even confidence and self-perception trigger our hormonal, neurobiological, and vascular systems—activating our flight-or-flight response, binding pain receptors to opioids, releasing sugar and adrenaline, or compromising our immune system.

Most importantly, researchers are beginning to step away from the antiquated notion that “voodoo” death and mind-body connections are limited to exotic cultures or foreign people.

Ted Kaptchuk, an associate professor at Harvard Medical School and a former practitioner of acupuncture and herbal medicine, observed this firsthand: Often, his patients would feel better after getting a consultation, before he had administered any treatment. “At the time the only possible explanation I had was that I was somehow a psychic healer—a role I did not care to embrace,” Kaptchuk says. “Afterward I was recruited to evaluate alternative therapies at Harvard Medical School, and it was there that I first learned about placebo effects.”

Now the director of Harvard’s placebo studies program, Kaptchuk points out that Western medicine, like tribal dance or shaman healing, is also enrobed in rituals that cause placebo effects. In a 2010 study, he split patients suffering from irritable bowel syndrome into three groups. One was given no placebo or consultation. The second was given a placebo treatment (fake acupuncture) with a brief consultation with a physician. The last group was given the same placebo treatment and a highly empathetic and warm patient-physician interaction; physicians spent extensive time asking the patient about how their IBS might be related to relationships and lifestyle, communicated confidence about the treatment, and actively listened to the patient.

Six weeks later, all three groups had improved, each one better than the last. In particular, patients who got the augmented relationship with their physician reported significantly more symptom relief and quality of life improvement than either group. With over 60 percent reporting adequate relief, their results were on par with any pharmaceutical ever tested for IBS treatment.

Kaptchuk isn’t necessarily saying that alternative medicine works. Instead, his point is that when we put our trust in healers or healing systems—whether it’s a physician in a white coat or a Navajo medicine man—we trigger neurobiological pathways that affect our body’s sensations and symptoms. It may seem unlikely that psychological stress could cause something as drastic and definite as death, but scientific research is slowly unveiling the possibility. And for illnesses that are highly subjective in nature or affected by stress, like headache, pain, depression, fatigue, and nausea, placebos could be our best bet.

“It’s a question of emphasis,” Kaptchuk says. “Placebo studies suggest that, in health care, a more balanced approach to the physical and mental would be helpful in making patients feel better.”

Mercy Medical Center, located in the Central Valley of California, began making this shift in 2009, when they started inviting shamans to the hospital to help treat Hmong patients. The shamans place lucky objects at doorways, perform healing ceremonies, and provide comfort and reassurance. The doctors heal the body—the shamans take care of the soul.