The role vitamin D plays in the pathogenesis of psoriasis is still a matter of debate. It has been previously reported that vitamin D is an important regulator of proliferation, differentiation and apoptosis of keratinocytes. Widespread use of topical vitamin D analogues supports the potential cause-and-effect relationship and therapeutic implications between vitamin D and psoriasis.
Narrowband (NB) UV-B is currently a standard of treatment when managing patients suffering from psoriasis. Previous studies have suggested that the effects of phototherapy in psoriasis could be mediated by the role NB-UV-B plays in vitamin D3(cholecalciferol) skin production. Indeed, the skin is a basic organ in the metabolism of vitamin D, being cutaneous production of vitamin D3 mediated by the action of UV-B wavelengths (290-315 nm) on the precursor 7-dehydrocholesterol. Of course, there are multiple variables that interact in this cutaneous function, among them the skin phototype, latitude and season of the year.
In the last August issue of the Archives of Dermatology, Ryan and co-workers have published a very interesting paper addressing these subjects. The main objectives of the study, as underlined by the authors, are the following:
- Primary objective: to determine whether or not the beneficial effects of NB-UV-B in psoriasis are related with vitamin D status improvement.
- Secondary objective: to study the role NB-UV-B may play in preventing deficits in vitamin D in patients during wintertime in mid to high latitudes, determining the serum levels of 25-hydroxyvitamin-D, 25(OH)D, the major vitamin D circulating form.
The effect of narrowband UV-B treatment for psoriasis on vitamin D status during wintertime in Ireland. Ryan C, Moran B, McKenna MJ, Murray BF, Brady J, Collins P, Rogers S, Kirby B. Archives of Dermatology 2010 Aug;146(8):836-842. Comment on: Phototherapy and vitamin D. Vemulapalli P, Lim HW. Archives of Dermatology 2010 Aug;146(8):906-908.
The authors designed a prospective randomized matched controlled study recruiting 60 patients with chronic plaque psoriasis from October 2008 to February 2009, in Dublin. 30 patients were treated with whole-body NB-UV-B, 3 times per week, until disease clearance. The remaining matched 30 patients, who had not received phototherapy or enjoyed sun holidays at least in the previous six months, were included in the control group. Treatment with drugs that may influence calcium metabolism was an exclusion criterion. Patients in the control group were treated with topical treatment, fumaric acid esters, methotrexate, acitretin, cyclosporine, or their combinations. A baseline metabolic profile was performed to every patient including levels of serum ionized calcium, serum phosphate, serum alkaline phosphatase (ALP), serum 25(OH)D, and serum intact parathyroid hormone (PTH). These were repeated at 4 weeks and at clearance of psoriasis, or when the corresponding control finished the study. The study took place in wintertime, in order minimize the role of terrestrial sunlight on serum 25(OH)D. Moreover, controls were recruited within a week of their corresponding patient to avoid the influence of intraseasonal variations in vitamin D.
One patient and her control were excluded from the study due to photoaggravated psoriasis. Serum 25(OH)D increased significantly (P<.001) at the end of NB-UV-B treatment compared with the control group. This change in circulating 25 (OH)D level was related with the number of phototherapy exposures (r=0.61;P<.001) and cumulative UV-B dose (r=0.47;P=.01). Interestingly, Ryan and co-workers did not find a correlation between serum 25(OH) levels and treatment response, measured by the number of exposures required to clear skin lesions or by changes in PASI/DLQI. Moreover, when the study concluded, 75% of the patients in the control group had serum 25(OH)D levels <20 ng/mL (vitamin D insufficiency), while every patient treated with phototherapy concluded the study with a status of vitamin D sufficiency. None of the patients developed hypercalcemia. Another two interesting results are underlined by the authors: in a multiple regression model the number of phototherapy exposures was the only factor that predicted increases in serum 25(OH)D level (r2=0.38;P=.001), and prior phototherapy was the only factor that predicted baseline 25(OH)D level (r2=0.13;P=.006).
In conclusion, as previously reported, Ryan and co-workers confirm that NB-UV-B significantly improves vitamin D status in psoriasis patients. Interestingly, the authors did not establish a causal relationship between the improvement provoked by phototherapy in psoriasis and the contemporaneous increase in vitamin D levels. The study confirms the importance of vitamin D deficits during wintertime in Ireland. This point is backed by the significant inverse correlation between circulating 25(OH)D and serum PTH levels. The authors support the need to consume milk enriched with vitamin D in high-latitude European countries during wintertime.