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Debunking Psoriasis Myths: Does UVB Phototherapy Cause Skin Cancer?
Myth: UVB phototherapy causes skin cancerPhototherapy is a common treatment modality for psoriasis patients that can be used in the physician’s...
From the Department of Dermatology and Venereology, Eskişehir Osmangazi University, Turkey.
The authors report no conflict of interest.
Correspondence: Işil Bulur, MD, Department of Dermatology and Venereology, Faculty of Medicine, Eskis¸ehir Osmangazi University, Ulusal Egemenlik St, Eskişehir, Turkey (isilbulur@yahoo.com).
The most effective UV wavelength for vitamin D synthesis is 295 to 300 nm, and therefore broadband UVB is frequently studied when determining the relationship between phototherapy and serum vitamin D levels.4 The current study demonstrated a statistically significant increase in serum 25(OH)D levels following NB-UVB treatment in patients with moderate to severe chronic plaque psoriasis (P<.001). This result supports other studies reporting that NB-UVB treatment in psoriasis patients increases serum 25(OH)D levels.13-18
The main factor in the effective UVB level for vitamin D synthesis is the angle at which solar radiation reaches the earth, which is affected by the longitude, latitude, and time of day.19 For this reason, we planned to perform our study at a single center. Patients who stayed in open areas for more than 2 hours per day during the summer months (May through September) were excluded from the study to decrease the effect of seasonal changes on vitamin D levels. We evaluated the seasonal variation of vitamin D levels and found no relationship between seasonal changes and serum 25(OH)D levels. Therefore, the potential effect of seasonal changes on the vitamin D levels of study participants was excluded from the study.
The response to UV radiation changes according to age and Fitzpatrick skin type because 7-dehydrocholesterol levels decrease with age and melanin prevents the access of UVB photons to 7-dehydrocholesterol.20 The basal serum 25(OH)D levels were deficient in 81.63% of participants and inadequate in 18.37%. In this study, we also observed that the basal serum 25(OH)D levels were significantly lower in patients with Fitzpatrick skin type II than in Fitzpatrick skin type I (P=.039). The mean (SD) serum 25(OH)D level at baseline was 14.14 (6.70) ng/mL and posttreatment was 46.42 (15.51) ng/mL in the 32 patients who completed the study. Serum 25(OH)D levels showed a statistically significant increase after NB-UVB treatment (P<.001). The increased serum 25(OH)D levels after NB-UVB phototherapy were not associated with Fitzpatrick skin type, which was consistent with the results of Osmancevic et al.17 The adjusted NB-UVB doses according to the different skin types might be responsible for this result in our study.
Participant age did not have a significant effect on serum 25(OH)D levels, similar to other studies in the literature.13,17 We believe that artificial UVB radiation at high doses can compensate for the 7-dehydrocholesterol that decreases in the skin with aging.
We observed no significant change in the serum calcium and phosphorus levels with NB-UVB treatment in our study. None of the participants had a metabolic disorder related to increased 25(OH)D levels. The serum ALP and PTH levels decreased significantly following treatment (P=.001 and P=.019, respectively), which may have been secondary to increased serum 25(OH)D levels.
Posttreatment serum 25(OH)D levels were compared with the number of NB-UVB phototherapy sessions and maximum dose values. The posttreatment serum 25(OH)D levels were found to be related to the number of sessions received, but this value was not correlated with the maximum dose received. The MED and maximum dose were determined according to the Fitzpatrick skin type of the participants. Therefore, increased serum 25(OH)D levels with an increased number of sessions was an expected result. Our observation is in accordance with the finding described by Ryan et al.14 On the other hand, an in vitro study conducted by Olds et al21 reported that the relationship between UV light and cholecalciferol synthesis was not linear.
We found that increased serum 25(OH)D levels after treatment were not correlated with the decrease in PASI score, similar to studies by Romaní et al18 and Ryan et al.14 These results suggest that the clinical improvement following NB-UVB treatment is independent of the increased serum 25(OH)D levels in psoriasis patients.
In conclusion, we found that the serum 25(OH)D levels that increase as a result of NB-UVB therapy for the treatment of chronic plaque psoriasis has no statistically significant relationship with the age, Fitzpatrick skin type, baseline PASI score, changes in PASI, or maximum dose, while a positive relationship is present between the serum 25(OH)D levels and the number of sessions of NB-UVB.
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