(A-C) Wildtype mice were exposed to broad spectrum intense light (10,000 lux) for 7 days (LD 14:10) and compared to controls that were maintained at room light (200 lux, LD 14:10). Total RNA was isolated from murine hearts using Qiazol Reagent and separated into mRNA and miRNA components following manufactures instructions (SA-Biosciences, Qiagen). cDNA from miRNA was generated using miScript RT II kits (Qiagen) and miR-21 or Per2 transcript levels were determined by real-time RT-PCR (iCycler; Bio-Rad Laboratories Inc.; mean±SD, n = 3, p<0.05). (D-F) 7 Healthy human volunteers were exposed to 30 minutes of intense blue light (Square One Wake Up Light, NatureBright, Day-Light 10,000 Lux) in the morning at 8:30 AM on 5 consecutive days. A blood draw was performed before light exposure on the first day (8:30 AM) and 5 days after light exposure (9.00 AM). Plasma samples were analyzed for miR-21 levels and PFK (phosphofructokinase) activity (mean±SD, n = 7, p<0.05).