Everything causes cancer, and everything doesn’t: Alcochol, but maybe not red wine, overeating but not getting enough veggies, too much sun, but also lack of vitamin D. Deciphering the headlines has become so burdensome that it’s nearly a meme. And increasingly when savvy readers see a headline “X causes cancer’ the result is more likely to be an eye roll than a urgent push to rid one’s life of the most recently publicized carcinogen.
But nevertheless, headlines ran earlier this week suggesting citrus fruits were the newest link to skin cancer. From the Daily Mail:
Drinking a glass of orange juice or eating a fresh grapefruit for breakfast may increase the risk of skin cancer, researchers say.
A glass of orange juice at least once a day increased the risk by 25 per cent, researchers found, according to HealthDay.
And those who ate whole grapefruit at least three times a week had a 41 per cent higher melanoma risk, versus those who never ate it, researchers found.
Those facts aren’t wrong, but we need to take a step back. The risk reported in the study of ever developing melanoma was extremely small, 1.7%. (It’s 2.1% over an American’s lifetime according to the CDC) So raising that risk, by even 41%, is also extremely small. Much less than the risk of developing breast or prostate cancer. Moreover, the increase in risk from citrus consumption was still dependent on sun exposure, which we know causes most melanomas and other skin cancer, the scientists wrote:
The positive association seemed to be more apparent among those who had higher sunburn susceptibility as a child or adolescent, those with a higher number of blistering sunburns, those who spent more time in direct sunlight, and those with higher annual UV flux at residence.
In other words, “the citrus can’t hurt you without the excessive sun exposure,” Abrar Qureshi the lead scientist told HealthDay.
The study also showed that eating a half of a grapefruit three times a week conveyed the highest risk, but drinking grapefruit juice in any amount didn’t add risk. Orange juice showed the opposite pattern with eating oranges adding no additional risk, but drinking orange juice being the second ‘most risky’ behavior. Researchers had a hard time reconciling this but did note that people drink a lot of orange juice, a fact also bemoaned by obesity researchers.
But before jumping to the conclusion that this might be a totally random effect, there are some reasons to go looking for a citrus-skin cancer connection. Citrus fruits, alongside carrots and celery (unreported in the study) contain high levels of chemicals called psoralens. These are known to make skin more sensitive to sunlight and are, in fact, the active ingredient in some tanning products. Lindsay Kobayashi explains at Public Library of Science:
Citrus fruits are high in psoralens, which are a group of naturally occurring chemical compounds called furanocoumarins. Furanocoumarins are the compounds that cause grapefruit to adversely interact with several medications in the gut (this is why grapefruit is not served in hospitals). Furanocoumarins increase skin photosensitivity when applied topically to the skin and also when taken orally.
And a message to stay away from fruits could have deleterious affects on health that are much more significant than the increased risk of melanomas. Last week the CDC released data that showed almost no one gets recommended amounts of fruit (1.5 to 2 cups) or vegetables (2 to 3 cups) in a day. Seventy six percent of us missed the fruit target and 87 percent didn’t get enough vegetables. And we missed by a lot. Most adults are getting less than half. Low produce intake is linked to a host of disease including stroke, heart disease and—you guessed it—cancer.
This study was a good study. It had a large sample size, fair reporting of the data, caveats described thoroughly by the authors within the paper itself and a plausible biological method of action via psoralens. But because of the rarity of melanoma and the size of the effects with citrus, the true impact is hard to gauge at best and minimal at worst. And they are so small compared to things we already know matter like protecting our skin from the sun. As nutritionist Marion Nestle told the Washington Post, “I’d worry much more about alcohol and cigarettes.”
Meredith Knight is a contributor to the human genetics section for Genetic Literacy Project and a freelance science and health writer in Austin, Texas. Follow her @meremereknight.