Grapefruit and Orange Juice Linked to Higher Risk of Melanoma

01 Jul 2015 --- Consuming large quantities of grapefruit and orange juices could lead to a higher risk of melanoma, a form of skin cancer, according to a new study published in the Journal of Clinical Oncology. 

The study found people who consumed high amounts of whole grapefruit or orange juice were over a third more likely to develop melanoma, compared with those who consumed low amounts.

However, lead study author Dr. Shaowei Wu, of the Department of Dermatology at the Warren Alpert Medical School of Brown University in Providence, RI, and colleagues stress that further research is needed before any changes are made to recommendations for orange and grapefruit consumption.

According to the American Cancer Society, 73,870 people in the US will be diagnosed with melanoma this year and 9,940 people will die from the cancer.
The primary risk factor for melanoma is exposure to ultraviolet (UV) radiation from the sun and indoor tanning devices, such as tanning beds and sun lamps.

Past research has suggested that tanning lotions containing psoralens - a group of naturally occurring substances called furocoumarins that are found in citrus fruits - may increase the risk of melanoma by sensitizing the skin to the effects of UV radiation.

For their study, Dr. Wu and colleagues set out to see whether consumption of citrus fruits may be associated with greater risk of melanoma.

The team analyzed data from 63,810 women who were part of the Nurses' Health Study between 1984 and 2010, as well as 41,622 men who were part of the Health Professionals Follow-Up Study between 1986 and 2010.

All participants completed dietary questionnaires at least every 4 years, from which the researchers were able to gather information on their citrus fruit intake. In the study, a serving of citrus fruit was defined as the equivalent to one orange, half a grapefruit or one 6 oz glass of whole orange or grapefruit juice.

The participants also completed health questionnaires every 2 years, which detailed lifestyle factors - such as smoking status and physical activity levels - and medical history. Subjects with a history of cancer were excluded from analysis.

During the 24-26-year follow-up, 1,840 participants were diagnosed with melanoma.

The researchers found that the more servings of oranges, grapefruits or juices from these fruits that the participants consumed overall, the higher their risk of melanoma. Subjects who consumed a serving of these fruits or their juices at least 1.6 times a day, for example, were found to be at 36% higher melanoma risk.

On analyzing melanoma risk by consumption of individual citrus products, the researchers found that grapefruit juice and whole oranges were not independently associated with greater risk of the cancer.

Eating whole grapefruit, however, was strongly associated with high melanoma risk, and this risk was found to be independent of confounding factors, such as age, smoking status, alcohol and coffee intake, use ofvitamin C supplements and physical activity levels.

Individuals more susceptible to sunburn as a child or teenager and those who had higher exposure to direct sunlight were at highest of melanoma from whole grapefruit consumption, the researchers found.

Orange juice was also associated with greater melanoma risk, which the researchers say is most likely because consumption of this product was much higher than consumption of other citrus products.

Though Dr. Wu and colleagues did not investigate the mechanisms underlying the association between citrus fruit consumption and melanoma risk, they speculate that it may be because the fruits are rich in psoralens and furocoumarins, which are believed to make the skin more sensitive to the sun.

"These substances are potential carcinogens, as found in both mice and humans. Psoralens and furocoumarins interact with UV light to stimulate melanoma cells to proliferate," explains Dr. Marianne Berwick, of the University of New Mexico in Albuquerque, in an editorial linked to the study.

However, the team notes no association was found between consumption of other foods rich in furocoumarins - such as celery and carrots - and increased risk of melanoma. But Dr. Wu says this is likely because people often cook these vegetables, and the heat reduces furocoumarin levels.