Could Grapefruit Lower Carcinoma Risk - but Be Linked to Melanoma?

Eating citrus in general found associated with higher risk of malignant melanoma, though past studies have found correlation between eating the peel and lowered carcinoma risk.

Limor Laniado Tirosh

People who eat citrus are ar higher risk of developing a certain skin cancer, according to a recent study, though whether the fruit actually caused the disease was not examined. The potential link between citrus consumption and malignant melanoma applied to both women and men.

Confusingly, earlier studies linked eating the peel of citrus to reduced risk of another skin cancer - squamous cell carcinoma. Life is complicated.

The new melanoma results, from an observational study that may not reflect the whole U.S. population, should be interpreted with caution, stated senior author Dr. Abrar Qureshi of the Warren Alpert Medical School of Brown University and Rhode Island Hospital, who worked on the study with the Channing Division of Network Medicine at Brigham and Women's Hospital in Boston.

Skin cancers – invasive melanoma among them – are a concern in sun-soaked Israel, and it's been on the rise, according to a data from 2010. That year, 207 Israelis died of various melanomas, though it bears saying that worldwide mortality rates from the cancer have been decreasing thanks to advances in treatment. In any case, although direct causes of a given person's condition can only be postulated, not proven - usually the culprit is considered to be the Middle Eastern sun, not oranges.

If anything, a study published in 2000 found that limonene - a chemical found in citrus peel – seemed to reduce the risk of squamous cell carcinoma of the skin. Eating the fruit or drinking the juice did nothing that the scientists noticed, but eating the peel did show intriguing diminishment of risk.

But there is a chemical explanation for the possible melanoma association. Fresh citrus contains furocoumarins, a family of photoactive compounds that can make an individual more sun-sensitive, and make sun exposure more damaging to skin cells, Qureshi told Reuters Health by email.

More citrus, more risk?
The new study reported in the Journal of Clinical Oncology possibly linking citrus consumption to melanoma did cover a lot of people: more than 63,000 women in the Nurses’ Health Study and 41,000 men in the Health Professionals Follow-Up Study, both of which ran from the mid-1980s to 2010.  

The participants answered questions about how frequently they consumed grapefruit, oranges, grapefruit juice or orange juice. The total of these four categories was considered an estimate of “overall citrus consumption,” although it does not include other citruses, like lemons and limes.

Over more than 20 years of follow-up, the researchers noted 1,840 cases of melanoma. Compared to people who ate citrus less than twice a week, those who ate citrus two to four times per week had a 10 percent increased risk of melanoma.

Melanoma risk increased as citrus consumption increased, rising to a 36 percent increase in risk for people who ate the fruits more than 1.5 times per day, on average. Of the citrus fruits, grapefruit seemed to have the strongest association with melanoma.

Even accounting for varying amounts of sun exposure and the geographic location of the study participants, the association between citrus fruits and skin cancer was still high, Qureshi said.

Still: “We are NOT recommending changing fruit consumption as these fruits and vegetables are important for overall health,” he said. “However, until we learn more about these furocoumarins, those consuming fresh citrus fruits on a regular basis should be extra careful with sun exposure, and depending on their outdoor activities they should wear appropriate sunscreen, hats and sun-protective clothing.”

With writing by Reuters