NEW YORK -- Have you heard that eating whole lemons prevents cancer? Or that bathing in Himalayan salt rids the body of harmful toxins? That eating hijiki seaweed can delay hair graying? If you have a few Facebook friends, you've probably encountered some of these claims. The website Natural News -- which seems like a parody but is unfortunately quite serious -- published these preposterous stories, and many others just as silly, last week alone.
Hokum like this is best ignored, but hundreds of thousands of Americans fail to do so. Natural News has achieved astonishing traction on social media, garnering Facebook shares in the high-five and low six figures. These numbers should trouble you -- Natural News has an uncanny ability to move unsophisticated readers from harmless dietary balderdash to medical quackery to anti-government zealotry.
Let's start by deconstructing the claim that eating whole lemons staves off cancer. The author cites two medical journal articles. She badly mischaracterizes the first, published in the Journal of Agricultural and Food Chemistry in 1999. The study described the isolation of three compounds, known as coumarins, from lemon peel. Coumarins exhibit tumor-suppressing properties in a laboratory dish, but that does not mean that eating lemon peel prevents cancer. Even if the oral ingestion of coumarins were convincingly shown to fight cancer in a laboratory animal, we still wouldn't know how much lemon peel would be required for a human to experience the same effects or whether you could tolerate the dose.
The second study the author cites is an enormous overreach. No one enjoys biostatistics, but bear with me and you'll be better prepared to identify weak studies in the future. The study, published in the journal Nutrition and Cancer in 2000, purported to show a correlation between consumption of lemon peel and diminished cancer risk. The authors surveyed 242 skin cancer survivors and 228 controls about their citrus consumption habits, but the questionnaire wasn't externally validated and has some screwy definitions. (Eating citrus peel "often," for example, is defined as "50-75 percent of the time." What does that mean?) The authors did not adequately control for race or skin tone, which is an important variable in skin cancer studies. The sample size was much too small. Only 163 of the 470 study participants reported eating citrus peel, and just 28 of them admitted to eating citrus peel often. That's not enough to prove that eating lemon peel prevents skin cancer. In addition, the statistical correlation is very weak, close to undetectable. Had one more person with cancer reported eating citrus peel, the relationship would likely have disappeared. In fairness, the study authors acknowledged the small sample size and the need for more substantial follow-ups, but everyone knows how these correlational studies are reported in the media. This is why you should look for patterns in scientific literature rather than relying on individual studies.
Anytime someone tells you that eating something prevents cancer, you should be skeptical. Natural News is full of these beauties. In addition to whole lemons, the site pushes organic green shakes, cilantro, blueberries and spirulina as surefire cancer fighters. Whisper it, though, because Natural News has exclusive information suggesting that the government will silence anyone who pushes natural cancer cures.
We'll never be rid of tripe like this -- shortcuts to immortality are irresistible -- but it's important not to confuse hopeful superstitions with science. If you loosen your grip on the anchor of evidence-based medicine, you'll find yourself drifting dangerously toward conspiracy theory.
You probably know what's coming next -- vaccines and autism, of course. Natural News loves to prey on vulnerable parents, and it's jumped all over questionable preliminary studies linking autism with everything from gluten to air pollution to antidepressants to the "Western lifestyle." But the site's drumbeat of support for the thoroughly debunked claim that vaccines cause autism is particularly shameful.
In case you've managed to miss this "controversy," a 1998 paper in the influential medical journal The Lancet claimed that the vaccine for measles, mumps and rubella caused autism. Sixteen years and many preventable measles outbreaks later, we know for certain that the claim is wrong. Literally hundreds of thousands of children have participated in studies around the world showing no association between vaccines and autism. A 2011 Institute of Medicine review of thousands of different studies reached the same conclusion. The Lancet has withdrawn the original paper and Andrew Wakefield, its author, lost his medical license, in part because he failed to disclose that lawyers preparing to sue vaccine manufacturers helped fund his research.
When one of your Facebook friends posts a link to a story about spirulina boosting brain function or how to cure pneumonia with vitamin C, I beg you to respond. A simple "bogus" will help halt their descent into insanity induced by Natural News. (That's a causal link you can believe in.)
• Palmer is Slate's chief explainer. He also writes How and Why and Ecologic for The Washington Post. Email him at explainerbriangmail.com.