Relationship between Furocoumarin Intake and Melanoma History among US Adults in the National Health and Nutrition Examination Survey 2003-2012

Furocoumarins potentiate UVA-induced DNA damage in skin melanocytes

Epidemiological studies have found that high citrus fruit consumption was associated with higher risk of skin cancer. Citrus fruits and some vegetables contain furocoumarins, which may interact with ultraviolet radiation to induce skin cancer. We aimed to determine the effects of two furocoumarins, including 8-methoxypsoralen (8-MOP) and 6',7'-dihydroxybergamottin (DHB), on UVA-induced DNA damage in human epidermal melanocytes, the origin of melanoma. Our hypothesis was that these dietary furocoumarins increase UVA-induced DNA damage in melanocytes, compared to cells exposed to UV alone. We incubated melanocytes with 8-MOP or DHB, followed by exposure to physiological doses of UVA radiation. We used Western blots to quantify the UVA-induced DNA damage measured by the fraction of phosphorylated histone variant H2AX (γH2AX), which is a marker of DNA damage, relative to total H2AX (γH2AX/H2AX) in the presence or absence of furocoumarins. To quantify the UVA-induced change in γH2AX/H2AX, we calculated the UVA:Control ratio as the ratio of γH2AX/H2AX in UVA-exposed cells to that in cells without UVA (control). The mean UVA:Control ratios were borderline significantly higher for cells treated with 8-MOP and significantly higher for cells treated with DHB, compared to that of untreated cells. This study suggests that furocoumarins (particularly 8-MOP and DHB) enhance UVA-induced DNA damage in melanocytes, which is a potential novel mechanism for citrus and furocoumarins to elevate the risk of skin cancer.

Association between Citrus Consumption and Melanoma Risk in the NIH-AARP Diet and Health Study

It has been hypothesized that consumption of citrus, a group of foods particularly rich in a class of photoactive compounds known as furocoumarins, may increase the risk of malignant melanoma. However, this hypothesis has not been rigorously studied in a general sample of US men and women. This study examined the relationship between citrus intake and melanoma risk in subjects of the NIH-AARP Diet and Health Study. Among 388,467 adults, 3,894 melanoma cases were identified during a median follow-up of 15.5 years. After adjustment for relevant potential confounders, total citrus consumption was not significantly associated with melanoma risk in this cohort. Among those with higher estimated exposure to ultraviolet radiation, and among those aged 60+ years at baseline, there were significant trends toward increased melanoma risk associated with whole citrus fruit consumption (P trends = 0.01 and 0.02, respectively), but the hazard ratios of the top consumers (2+ cups per week) vs. nonconsumers were nonsignificant. Further research is needed to explore associations of citrus with melanoma risk among older adults and those with high sun exposure.

Intake of Furocoumarins and Risk of Skin Cancer in 2 Prospective US Cohort Studies

BACKGROUND

In prior studies, higher citrus consumption was associated with higher risk of cutaneous malignant melanoma, squamous cell carcinoma (SCC), and basal cell carcinoma (BCC). Furocoumarins, compounds with phototoxicity and photocarcinogenicity in citrus, may be responsible for the association.

OBJECTIVES

The objective of the study was to investigate the association between furocoumarin intake and skin cancer risk.

METHODS

A total of 47,453 men from the Health Professionals Follow-Up Study (HPFS) and 75,291 women from the Nurses' Health Study (NHS) with diet data collected every 2-4 y in the 2 prospective cohort studies were included. A furocoumarin food composition database for 7 common furocoumarins [bergaptol, psoralen, 8-methoxypsoralen, bergapten, 6',7'-dihydroxybergamottin (6'7'-DHB), epoxybergamottin, and bergamottin] was developed and used to calculate participants' cumulative average and energy-adjusted furocoumarin intake. Multivariate HRs and 95% CIs of the associations between furocoumarin intake and skin cancer risk were estimated using Cox proportional hazards models. Analyses were performed separately in each cohort as well as pooled using a fixed-effects model.

RESULTS

Throughout follow-up (1984-2012 in the NHS and 1986-2012 in the HPFS), we identified 1593 melanoma, 4066 SCC, and 28,630 BCC cases. Higher intake of total furocoumarins was associated with an increased risk of BCC; the pooled HR comparing the top with the bottom quintile was 1.16 (95% CI: 1.11, 1.21; P-trend = 0.002). Higher intakes of bergaptol, bergapten, 6'7'-DHB, and bergamottin were also significantly associated with increased BCC risk. No significant associations were found between intake of total furocoumarins and the risks of SCC or melanoma.

CONCLUSIONS

Intakes of total furocoumarins as well as some individual furocoumarins were associated with an increased risk of skin cancer, especially BCC, in 2 cohorts of US health professionals.