Nearly half of Americans believe in medical conspiracy theories

About half of all American adults believe in at least one medical conspiracy theory, according to a study from researchers at the University of Chicago in Illinois and published in JAMA Internal Medicine.

Conspiracy theories concerning aliens, secret societies and shadowy governmental organizations have become a firm trope in popular culture thanks to cult television shows, novels and movies like The X-Files and The Da Vinci Code. But conspiracy theories have also sprouted up around numerous public health concerns over the past 50 years.

Water fluoridation, vaccines, cell phones and alternative medicine, for instance, are all subjects of conspiracy-based speculation, but to what extent do the American public put faith in these uncorroborated theories?

The University of Chicago's Prof. J. Eric Oliver put this to the test in his new study. Prof. Oliver and his colleague used an online survey to collect data from 1,351 adults between August and September 2013.

In the survey, participants were presented with popular medical conspiracy theories and asked to indicate whether they had heard of them before and whether they agreed or disagreed with them.

The theories all had a mistrust of government and large organizations as central themes. Some of the theories the participants were asked if they believed included:

- Are US regulators preventing people from getting natural cures?
- Did a US spy agency infect a large number of black Americans with human immunodeficiency virus (HIV)?
- Does the government knowingly give autism-causing vaccines to children?
- Does the government know that cell phones cause cancer but does nothing about it?
- Do companies dump dangerous chemicals into the environment under the guise of water fluoridation?

Overall, 49% of participants agreed with at least one of the theories.

Some of the theories were more well known than others. For instance, 69% of participants had heard of the idea that childhood vaccines cause psychological disorders, such as autism.

This is a theory that has received a lot of media attention and is in the news again at the moment due to controversial Twitter comments from TV presenter Jenny McCarthy. Of the study participants, 20% agreed with this theory and 44% disagreed.

More popular was the theory that US regulators are stopping people from accessing natural cures - 37% of people agreed with this idea, with less than a third disagreeing.

The least popular conspiracy theory - which more than half of the participants disagreed with - was the suggestion that a US spy agency had infected a large number of black Americans with HIV.

What impact do conspiracy theories and belief in them have on people's health?

"Science in general - medicine in particular - is complicated and cognitively challenging because you have to carry around a lot of uncertainty," Prof. Oliver says of the prevalence in conspiracy theory beliefs. "To talk about epidemiology and probability theories is difficult to understand as opposed to 'if you put this substance in your body, it's going to be bad.'"

As well as illustrating that medical conspiracy theories are perhaps more widely believed than had previously been thought, Prof. Oliver's study also found some interesting associations between belief in conspiracy theories and the way people approached their own health.

One example of this is that 35% of people who believed in three or more conspiracy theories took herbal supplements, whereas only 13% of people who did not believe in any conspiracy theories took supplements. People who believed in conspiracy theories were also more likely to use alternative medicine and avoid traditional medicine.

The study concludes:

"Although it is common to disparage adherents of conspiracy theories as a delusional fringe of paranoid cranks, our data suggest that medical conspiracy theories are widely known, broadly endorsed, and highly predictive of many common health behaviors."

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