Low-Dose Narrowband UVB Exposure Modulates Systemic Metabolism in Mice

Ultraviolet B (UVB) light exerts biological effects beyond the skin; however, its influence on systemic energy metabolism remains unclear. We investigated the effects of chronic, low-dose narrowband UVB irradiation on substrate utilization, circulating metabolites, and thermogenesis of brown adipose tissue (BAT) in mice. Male and female C57BL/6J mice were daily exposed to sub-erythemal UVB (308 nm, 50 or 100 mJ/cm2, 3 h) for up to 7 weeks using a custom light-emitting diode-based device. Metabolic outcomes were assessed by indirect calorimetry, locomotor activity monitoring, and infrared thermography. Plasma metabolites were profiled by capillary electrophoresis–time-of-flight mass spectrometry. Gene expression in BAT and skin was measured by reverse transcription quantitative polymerase chain reaction. UVB exposure lowered the respiratory exchange ratio at specific time points, indicating greater lipid utilization, and transiently increased oxygen consumption. Metabolomic profiling revealed reduced succinate levels and enrichment of nicotinate/nicotinamide and propanoate metabolism pathways. Infrared thermography showed elevated surface temperature after irradiation and that prolonged UVB exposure modestly upregulated thermogenic genes in BAT, along with increased cutaneous expression of Cidea. These findings suggested that sub-erythemal UVB exposure modestly modulates systemic metabolism, circulating metabolites, and BAT activity, highlighting UVB as a potential environmental regulator of energy balance.