Circadian Light Hygiene Associates with Anemia Markers in Young Adults

This study investigated the association of circadian light exposure (LE), blue light exposure (BLE), sleep, and physical activity (PA) with hematological markers in 85 young adults (18–25 years) living at a high latitude. Participants underwent 7-day monitoring with actigraphy and RGB sensors, alongside morning blood sampling for hemoglobin (HGB), hematocrit (HCT), mean corpuscular hemoglobin (MCH), and variability in red blood cell distribution width (RDW-CV). Univariate analyses revealed that the normalized BLE amplitude (NA BLE) positively correlated with HGB (r = 0.369, p = 0.001) and MCH (r = 0.378, p < 0.001). A later BLE acrophase negatively correlated with lower HGB (r = –0.322, p = 0.003), and MCH (r = –0.272, p = 0.013), but positively with larger RDW-CV (r = 0.291, p = 0.008). A later PA acrophase associated with lower MCH and larger RDW-CV, while a later bedtime correlated with lower HGB and MCH. Multivariate regressions (adjusted for sex/age) confirmed that a larger NA BLE predicted higher HGB (β = 0.206, p = 0.037) and MCH (β = 0.377, p < 0.001), and that an earlier BLE acrophase predicted higher MCH (β = –0.304, p = 0.008) and smaller RDW-CV (β = 0.316, p = 0.006). These findings highlight that advantageous circadian patterns of BLE and activity are linked to a favorable hematological status.