Citrus Fruit Consumption May Be Linked to An Increased Risk of Melanoma
A large population-based prospective analysis of the consumption of psoralen-rich citrus products and the risk of malignant melanoma has found that the melanoma risk was 36% higher in people who consumed citrus fruit or juice at least 1.6 times daily compared with those who consumed it less than twice per week. Among individual citrus products, grapefruit and orange juice showed the most association with the risk of melanoma. The link between melanoma and citrus fruit consumption, according to the study, may be due to the high levels of psoralens—a group of naturally occurring furocoumarins, which make the skin more sensitive to sunlight—found in citrus fruits.
Previous studies have shown that people using psoralen-containing sunscreen had a substantially increased risk of melanoma compared with regular sunscreen users. The current study by Wu et al is published in the Journal of Clinical Oncology.
Study Methodology
The researchers collected the medical history, lifestyle risk factors, and dietary intake of 63,810 women in the Nurses’ Health Study (NHS) and 41,622 men in the Health Professionals Follow-Up Study (HPFS). Information on participants’ medical history and lifestyle factors was collected biennially via mailed questionnaires. Dietary intake was assessed using a validated food frequency questionnaire at least every 4 years. The researchers observed participants for incident melanoma starting from 1984 in the NHS and 1986 in the HPFS, when the participants completed a baseline food frequency questionnaire with detailed information on citrus consumption.
The study participants had no history of any cancer, including nonmelanoma skin cancers, and were Caucasian.
Study Findings
Over 24 to 26 years of follow-up, the researchers documented 1,840 incidents of melanoma. After adjustment for other risk factors, the pooled multivariable hazard ratios for melanoma were 1.00 for overall citrus consumption less than twice per week (reference), 1.10 (95% confidence interval [CI] = 0.94–1.30) for two to four times per week, 1.26 (95% CI = 1.08–1.47) for five to six times per week, 1.27 (95% CI = 1.09–1.49) for once to 1.5 times per day, and 1.36 (95% CI = 1.14–1.63) for ≥ 1.6 times per day (P < .001).
Among individual citrus products, grapefruit showed the most apparent association with risk of melanoma, which was independent of other lifestyle and dietary factors. The pooled multivariable hazard ratio for melanoma comparing the extreme consumption categories of grapefruit (three or more times per week vs never) was 1.41 (95% CI = 1.10–1.82; P < .001).
Orange juice consumption also showed a significant but less apparent association with melanoma risk. Interestingly, consumption of grapefruit juice and oranges was generally not associated with melanoma risk.
“These findings provide evidence for the potential photocarcinogenic effect of psoralen-rich foods. However, previous studies have also suggested that fruit intake may have potential beneficial effects for the prevention of chronic diseases, such as breast cancer and type 2 diabetes. Although our findings are consistent with evidence from animal experiments, which revealed a potential synergistic effect between psoralens and UV radiation, further investigation is needed to confirm our finding and guide sun exposure behaviors among individuals with high citrus consumption,” concluded the study authors.
Study Strengths and Limitations
In an accompanying editorial, Marianne Berwick, PhD, MPH, Distinguished Professor in the Department of Internal Medicine and Dermatology at The University of New Mexico, said that although the study's large size and prospective nature added to its strengths, there were several limitations. The most important one, said Dr. Berwick, is that the study population is not representative of the general population.
She said that this is a potentially important study because citrus consumption is widely promoted as an important part of a healthy diet that has demonstrated benefit for coronary heart disease, cancer prevention, and overall health effects.
“At this point in time, a public overreaction leading to avoidance of citrus products is to be avoided,” wrote Dr. Berwick. “For people who would be considered at high risk, the best course might be to advise individuals to use multiple sources of fruit and juice in the diet and to use sun protection, particularly if one is sun sensitive. There is clearly a need for replication of the study findings in a different population before modifying current dietary advice to the public.”
Abrar A. Qureshi, MD, MPH, of Warren Alpert Medical School at Brown University, is the corresponding author of this study.
This study was funded in part by the National Cancer Institute. For full disclosures of the study authors, visit jco.ascopubs.org.
The content in this post has not been reviewed by the American Society of Clinical Oncology, Inc. (ASCO®) and does not necessarily reflect the ideas and opinions of ASCO®.
