Citrus and melanoma...

There was a great hubbub on this topic in 2015.  Last year, there was this:  Tangy, tart and sweet! Does citrus intake cause increased risk of skin cancer and melanoma?

Now, this:  

The association between citrus consumption and melanoma risk in the UK Biobank.  Marley, Li, Champion, et al. Br J Dermatol.  Aug 2021.

Background: Melanoma incidence has been dramatically increasing worldwide. Psoralen, a known photocarcinogen, is naturally abundant in citrus products, leading to the hypothesis that high citrus consumption may increase melanoma risk.

Objectives: To investigate the association between total citrus consumption and melanoma risk, and the association between individual citrus products and melanoma risk, and to test for interactions between total citrus intake and established melanoma risk factors.

Methods: Logistic regression was used to estimate odds ratios (ORs) and 95% confidence intervals (CIs) for the association between citrus consumption and melanoma risk among 1592 cases and 197 372 controls from the UK Biobank cohort. Citrus consumption data were collected via five rounds of 24-h recall questionnaires. International Classification of Diseases codes were used to determine melanoma outcome.

Results: After adjusting for potential confounders, participants in the highest category of total citrus intake (greater than 2 servings per day) had a significantly increased risk of melanoma relative to those with no consumption. For individual citrus products, participants with the most orange and orange juice consumption (greater 1 serving per day) had a significantly increased melanoma risk relative to those with no consumption. Fair- or very fair-skinned participants with high citrus consumption had an even greater melanoma risk.

Conclusions: High citrus consumption was associated with an increased risk of melanoma in a large, prospective, population-based cohort. Further validation of these findings could lead to improved melanoma prevention strategies.

Again - hmmm...  Well, here's what Wiki has to say about Psoralen:

Psoralen (also called psoralene) is the parent compound in a family of naturally occurring organic compounds known as the linear furanocoumarins. It is structurally related to coumarin by the addition of a fused furan ring, and may be considered as a derivative of embelliferone. Psoralen occurs naturally in the seeds of Psoralea corylifolia, as well as in the common fig, celery, parsley, West Indian Satinwood, and in all citrus fruits. It is widely used in PUVA (psoralen + UVA) treatment for psoriasis eczema, vitiligo, and cutaneous T-cell lymphoma; these applications are typically through the use of medications such as Methoxsalen. Many furanocoumarins are extremely toxic to fish, and some are deposited in streams in Indonesia to catch fish.

Despite the photocarcinogenic properties of psoralen, it was used as a tanning activator in sunscreens until 1996. [WOW!] Psoralens are used in tanning accelerators, because psoralen increases the skin's sensitivity to light. Some patients have had severe skin loss after sunbathing with psoralen-containing tanning activators. Patients with lighter skin color suffer four times as much from the melanoma-generating properties of psoralens than those with darker skin.

So....when using this as therapy, the psoralen is taken as an oral medication, making the skin more sensitive to UVA rays, to which it is then exposed.  This PUVA treatment can help manage psoriasis, but can cause skin issues ranging from itching, blistering and darkening to squamous cell skin cancer and melanoma.  Nausea is also frequent - apparently.  This same therapy is said to aid repigmentation of vitiligo affected skin in 20% of cases.  

Interestingly, this is the compound that has been responsible for the brown dribbles of discoloration I've seen on the hands, necks and faces of little ones brought in by their disturbed parents.  A little investigation would reveal that, yes, they had in fact sat in the sun on their front step as they enjoyed sucking on lemons and limes.  My diagnosis - phytophotodematitis.

My question in regard to citrus intake and melanoma is this:  Does citrus intake, thereby the increased intake of psoralen, have the risk of melanoma if one avoids sun exposure?  I don't know the answer to that one.

Says the girl who had grapefruit for breakfast, lime in her water at lunch, and lemon on her chicken at dinner!!!

For what it's worth! - c