Serum levels of folate, 25‐hydroxyvitamin D3 and cobalamin during UVB phototherapy: findings in a large prospective trial

BACKGROUND: Narrowband UVB phototherapy (NB-UVB) is a mainstay in the treatment of numerous inflammatory dermatoses. Whereas, a wealth of studies has shown that NB-UVB treatment increases 25-hydroxyvitamin D3 (25(OH)D) levels, only sparse and controversial data exist on its effect on serum folate and cobalamin. OBJECTIVES: To determine whether exposure to NB-UVB alters serum folate or cobalamin levels. METHODS: A single-centre, prospective, open observational study on 101 patients subjected to NB-UVB phototherapy between late fall and early spring. Serum folate, 25(OH)D and cobalamin levels were measured after 0, 12, 24 and 36 NB-UVB exposures. RESULTS: After 12 NB-UVB exposures a significant decrease of mean serum folate (-1.0 nmol/L; P = 0.03) and cobalamin (-14.5 pmol/L, P = 0.03) levels was observed whereas serum levels of 25(OH)D showed a significant increase (35.4 nmol/L, P < 0.0001). CONCLUSIONS: A standard course of NB-UVB induces a small but significant decrease of serum folate and cobalamin levels.