Plasma β-endorphin levels in frequent and infrequent tanners before and after ultraviolet and non-ultraviolet stimuli

To the Editor: Ultraviolet (UV) exposure behavior exhibits similarities to other substance-related disorders.1 UV exposure has a direct reinforcing effect on frequent tanners.2 Cutaneous opioids are induced by UV exposure,3 but whether the reinforcement seen with UV exposure is caused by opioid release is unknown. The potential relationship is complicated, as larger studies have not found an effect of UV on plasma β-endorphin levels.4 These conflicting results could be caused by differences in UV dose and subject populations, because the tests were not done under conditions in which preference for the UV stimulus was known to occur.

To better understand the relationship between cutaneous opioids and the reinforcing effect of UV exposure, we conducted a small double-blind, placebo-controlled, randomized trial and assessed plasma β-endorphin levels in 3 frequent and 3 infrequent adult female tanners, between 25 and 32 years of age and skin types III and IV, before and after non-UV and UV exposures (10 min for frequent tanners and 5-9 min for infrequent tanners based on minimal erythema dose testing). The study was approved by the Institutional Review Board (IRB). Infrequent tanners were defined as individuals who had tanned intermittently in the past (fewer than 8 times per year) but who are not regular tanners. Frequent tanners were defined as tanners who tan more often than is necessary to maintain a tan (8-15 times per month). Commercial indoor tanning beds with Speed 175 and 205 bulbs were used. The bulbs have a UV output of 4% in the UVB range and 96% in the UVA range (estimate dosage of 22.4 j/cm2). Plasma β-endorphin levels were measured on the same day by enzyme-linked immunosorbent assay (MD Biosciences Inc, St Paul, Minn) from blood samples drawn 3 times: before exposure, immediately after non-UV bed, and immediately after UV bed.

No discernable trend in plasma β-endorphin levels was observed among the 6 subjects (Fig 1), though the mean plasma β-endorphin level was slightly higher in frequent tanners exposed to UV as compared to baseline. Baseline β-endorphin levels vary and exhibit no distinct pattern of response to UV exposure (at one exposure time in these 6 subjects). The variability in plasma β-endorphin levels complicates attempts to understand the role of endorphins in mediating the preference for UV. Even anxiety about the blood draw could affect endorphin levels. Opioid inhibitor studies may be a better approach to characterize the role of endorphin related effects in mediating physiologic responses to UV.

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Fig 1. Plasma endorphin levels in 3 frequent and 3 infrequent tanners. Circles represent frequent tanners and squares represent infrequent tanners. No clear, discernable pattern to the response to UV exposure was identified in this small group.