People who consume large amounts of citrus, either as juice or in fruit, may have an increased risk of getting melanoma, the most dangerous type of skin cancer, researchers say.
In a study of 100,000 Americans, an unexpected association was found between high consumption of citrus, specifically orange juice or whole grapefruit, and risk of melanoma, they say.
A 36 percent higher risk of the cancer was seen in those who had a serving of citrus fruit or juice 1.6 times each day when compared with who had a serving less than two times a week, the researchers report in the Journal of Clinical Oncology.
They were quick to emphasize that a link or association is not the same thing as determining a true cause-and-effect relationship.
"At this point in time it is not a good idea to avoid citrus fruits," said study researcher Dr. Walter Willett of the Harvard School of Public Health, noting the many known health benefits of citrus.
However, the researchers pointed out a plausible mechanism for how citrus might increase a skin cancer risk.
Oranges and grapefruit contain "photoactive" compounds that can affect the skin and its cells, they explain; one is furocoumarins, which can make the skin more sensitive to sunlight.
The other is psoralen, which along with furocoumarins can cause melanoma cells to multiply.
Until 1996, psoralen had been added to suntan lotion as a tanning activator.
Their presence in citrus has been demonstrated to affect the skin, says researcher and dermatologist Dr. Abrar Qureshi from Brown University.
"You'll see children get a sunburn in spots where a citrus popsicle dripped down the chin, for example," he points out.
Overall, the risk of melanoma is small - fewer than 2 percent of the 100,000 people in the 25-year study got melanoma.
Although the findings are "intriguing," it's far too soon for any changes to dietary recommendations regarding grapefruit and oranges, the American Society of Clinical Oncology said in a statement.
"At this time, we don't advise that people cut back on citrus - but those who consume a lot of grapefruit and/or orange juice should be particularly careful to avoid prolonged sun exposure," says Brown lead researcher Shaowei Wu.
Qureshi agrees, urging people to protect their skin by limiting their sun exposure, staying in the shade, wearing a hat and using sunscreen.
"We certainly wouldn't want people to avoid fruits that are generally good for their health," he says. "Just be aware that there's an association with melanoma, and perhaps be extra careful about sun protection on days you're eating citrus fruits."