The placebo effect is widely recognized and frequently utilized in modern medicine. People given a "sugar" pill but told it's a powerful antidote to their illness very frequently experience a cure rate similar to those given a real medical proven treatment. Our minds seem to have a degree of control over our health that we don't understand.
There's a flip side to this though. People's belief that certain actions are harmful or spiritually dangerous can kill them as effectively as a placebo can cure them. The harmful version of the placebo effect is called the "nocebo".
Alexis Madrigal reports on research into the unexpected nighttime deaths of men of the Hmong community as they emigrated to the United States following the end of the Vietnam War in the 1970's.
"Some Hmong felt that they had not properly honored the memories of their ancestors, which was a known risk factor among the Hmong for being visited by the tsog tsuam. Once the night-mare visitations began, a shaman was often needed to set things right. And in the scattered communities of Hmong across the country, they might not have access to the right person. Without access to traditional rituals, shamans, and geographies, the Hmong were unable to provide themselves psychic protection from the spirits of their sleep.
Drawing on all this evidence, Adler makes the provocative claim that the Laotian immigrants of the 1980s were in some sense killed by their powerful cultural belief in night spirits. It was not a simple process.
"It is my contention that in the context of severe and ongoing stress related to cultural disruption and national resettlement (exacerbated by intense feelings of powerlessness about existence in the United States), and from the perspective of a belief system in which evil spirits have the power to kill men who do not fulfill their religious obligations," Adler writes, "the solitary Hmong man confronted by the numinous terror of the night-mare (and aware of its murderous intent) can die of SUNDS."
Her argument amounts to a stirring and chilling case for the power of the nocebo, the flipside to the placebo effect. While placebo studies have grown in importance, the nocebo effect has not been studied well in scientific literature, in part because of the ethical issues involved in deliberately doing something that might harm people. Limited studies suggest that it is real and it is powerful. For example, doctors have found that patients made to feel anxious need larger amounts of opiates after surgery than other people. They've found that pretending to expose people who say they are sensitive to electromagnetic radiation to cell phone signals can give them debilitating headaches. Even patients' level of side effects from arthritis medication seem determined by those patients' beliefs about those medicines. Logically speaking, if the evidence shows the upside of belief, why wouldn't we believe in the downside, too? And why wouldn't we believe that the intensity of the downside would vary with the intensity of the belief, even if those beliefs were about something unscientific, like spirits or astrology?
If you're still unsure that the nocebo effect could actually lead to premature death, Adler cites one stunning example of the effect from China. A team of researchers found that Chinese Americans die younger than expected "if they have a combination of disease and birth year which Chinese astrology and medicine considers ill-fated." That is to say, if they were born in a year that was astrologically linked to poor lung health, they would die an average of five years earlier from lung-related disease than someone born in some other year with the same disease. Similar effects were not found in the white populations around them. And how much sooner you died depended on the people's "strength of commitment to traditional Chinese culture.""
Voodoo practice in Haiti, or cursing by "witch-doctors" in Africa are similar examples of this effect. And having worked as a volunteer chaplain to seafarers years ago, crews who believe their ship is "cursed" or haunted are much more likely to suffer serious accidents during their travels than those who don't.
In light of all this the rituals of anointing the sick in the hospital, blessing the frightened and forgiving the sins of the penitent, viewed by some as superstitious twaddle, are seen as powerful tools to save people's lives.