Will these research results hold up over time? It is known that certain fruits (citrus fruits and juices) and vegetables contain photosensitizing chemicals called psoralens, and the researchers suspected that a high intake of citrus products over time could make individuals more susceptible to melanoma than people who rarely ate citrus fruits. During more than 2 decades of following more than 100,000 persons they found 1840 melanomas , And yes, even though there were relatively few melanomas, they did find a dose-dependent relationship between citrus product consumption and melanoma risk, specifically that ingesting citrus fruit 1.6 or more times per day had a 36% higher risk for melanoma than people who ate it less than twice per week. But this association was only with whole grapefruit and orange juice, and weirdly, not with consumption of grapefruit juice or whole oranges. Before people panic, remember that citrus fruits have all sorts of great health benefits and should be eaten. From Science Daily:
People who enjoy a glass of orange juice or some fresh grapefruit in the morning may face a slightly increased risk of melanoma—the least common but most deadly form of skin cancer. That's the finding from a study of more than 100,000 U.S. adults followed for about 25 years. Researchers discovered that those who regularly consumed orange juice or whole grapefruit had a higher risk of developing melanoma, compared to people who avoided those foods.
Experts were quick to stress that the findings, reported online June 29 in the Journal of Clinical Oncology, do not prove that citrus foods help cause skin cancer. It is plausible, however, that certain compounds in citrus explain the association, said senior researcher Dr. Abrar Qureshi, chair of dermatology at Brown University and a dermatologist at Rhode Island Hospital, in Providence.
Citrus foods contain particular "photoactive" chemicals—namely, psoralens and furocoumarins—that are known to make the skin more sensitive to the sun when they're applied topically, Qureshi said."You'll see children get a sunburn in spots where a citrus popsicle dripped down the chin, for example," Qureshi explained.
But even if citrus foods potentially make some people susceptible to sunburn, it's not orange juice that should be avoided, Qureshi said. "The citrus can't hurt you without the excessive sun exposure," he pointed out. So the message remains the same, Qureshi said: Protect your skin from soaking up too many rays by staying in the shade, using sunblock and wearing a hat. "I don't think the general public should make any changes based on this study," said Berwick, a professor of dermatology at the University of New Mexico in Albuquerque.
For the study, the researchers analyzed data from two long-running studies of U.S. health professionals. Every couple of years, the participants answered detailed surveys on their health and lifestyle. Over about 25 years, more than 1,800 people developed melanoma and the risk was higher among those who regularly drank orange juice or ate whole grapefruit. That was true, the researchers found, even when several other factors were taken into account—including people's reports of their overall sun exposure and history of bad sunburns.
People who had orange juice at least once a day were about 25 percent more likely to develop melanoma than those who drank the juice less than weekly. Similarly, people who ate whole grapefruit at least three times a week had a 41 percent higher melanoma risk, versus those who never ate it. On the other hand, there was no connection between melanoma risk and either whole oranges or grapefruit juice, the researchers found.
Qureshi did offer a potential explanation for why only orange juice and whole grapefruit may be tied to melanoma risk."There are different types of these photoactive compounds in different parts of the fruit," he said. So, it's possible that not all citrus fruits are alike when it comes to melanoma risk. Plus, Qureshi said, heat—like that used in pasteurizing juice—neutralizes the photoactive compounds. That might help explain why grapefruit juice was not connected to melanoma risk.