UVB-exposed wheat germ oil increases serum 25-hydroxyvitamin D(2) without improving overall vitamin D status: a randomized controlled trial

PURPOSE: This study investigated whether UVB-exposed wheat germ oil (WGO) is capable to improving the vitamin D status in healthy volunteers. METHODS: A randomized controlled human-intervention trial in parallel design was conducted in Jena (Germany) between February and April. Ultimately, 46 healthy males and females with low mean 25-hydroxyvitamin D (25(OH)D) levels (34.9 ± 10.6 nmol/L) were randomized into three groups receiving either no WGO oil (control, n = 14), 10 g non-exposed WGO per day (– UVB WGO, n = 16) or 10 g WGO, which was exposed for 10 min to ultraviolet B-light (UVB, intensity 500–630 µW/cm(2)) and provided 23.7 µg vitamin D (22.9 µg vitamin D(2) and 0.89 µg vitamin D(3)) (+ UVB WGO, n = 16) for 6 weeks. Blood was obtained at baseline, after 3 and 6 weeks and analyzed for serum vitamin D-metabolite concentrations via LC–MS/MS. RESULTS: Participants who received the UVB-exposed WGO were characterized by an increase of circulating 25(OH)D(2) after 3 and 6 weeks of intervention. However, the 25(OH)D(3) concentrations decreased in the + UVB WGO group, while they increased in the control groups. Finally, the total 25(OH)D concentration (25(OH)D(2) + 25(OH)D(3)) in the + UVB WGO group was lower than that of the non-WGO receiving control group after 6 weeks of treatment. In contrast, circulating vitamin D (vitamin D(2) + vitamin D(3)) was higher in the + UVB WGO group than in the control group receiving no WGO. CONCLUSION: UVB-exposed WGO containing 23.7 µg vitamin D can increase 25(OH)D(2) levels but do no improve total serum levels of 25(OH)D of vitamin D-insufficient subjects. TRIAL REGISTRATION: ClinicalTrials.gov: NCT03499327 (registered, April 13, 2018). SUPPLEMENTARY INFORMATION: The online version contains supplementary material available at 10.1007/s00394-022-02827-w.