In Arctic residents, blood lipids fluctuate seasonally in response to changes in light exposure (LE) patterns. This study investigates which aspects of LE (timing, dynamic range, and duration) are related to lipid profiles. We analyzed actigraphy data measuring LE and blue light exposure (BLE) along with blood determinations from 27 residents across different seasons. We assessed circadian parameters of melatonin in a subset of participants. We found that features of BLE and melatonin significantly predicted lipids: An earlier BLE acrophase was associated with higher HDL-C (β = −0.246, p = 0.013). Nighttime BLE was positively associated with TC (β = 0.290, p = 0.008) and LDL-C (β = 0.253, p = 0.025). The normalized circadian amplitude of BLE was inversely associated with the TG/HDL ratio (β = −0.384, p < 0.001). Finally, earlier melatonin was associated with lower TG/HDL (β = 0.464, p = 0.007). Results remained significant after adjusting for co-factors of photoperiod duration, age, sex, and indigeneity. These findings suggest that patterns of LE (circadian light hygiene) could be a way to improve cardiovascular health.

In this work we report solvatochromic and luminescent properties of ethyl N-salicylideneglycinate (1), ethyl N-(5-methoxysalicylidene)glycinate (2), ethyl N-(5-bromosalicylidene)glycinate (3), and ethyl N-(5-nitrosalicylidene)glycinate (4) dyes. 1–4 correspond to a class of N-salicylidene aniline derivatives, whose photophysical properties are dictated by the intramolecular proton transfer between the OH-function and the imine N-atom, affording tautomerization between the enol-imine and keto-enamine forms. Photophysical properties of 1–4 were studied in different pure non-polar and (a)protic polar solvents as well as upon gradual addition of NEt₃, NaOH, and CH₃SO₃H. The DFT calculations were performed to verify the structures of 1–4 as well as their electronic and optical properties.

Background — Light exposure (LE) critically regulates circadian rhythms, influencing sleep, mood, metabolism, and longevity. Quantifying circadian light hygiene is challenging due to high inter-individual variability. The Normalized Amplitude of Blue Light Exposure (NA BLE) metric provides a standardized assessment of BLE dynamics and range. We evaluated NA BLE in high-latitude Arctic residents, leveraging extreme seasonal light variations as a natural experiment to characterize its seasonal dependencies and associations with circadian parameters. Methods — Twenty-seven healthy Arctic adults underwent longitudinal assessment across seasons, spanning winter solstice, spring equinox, and summer solstice. Wrist actigraphy (ActTrust 2) captured physical activity (PA), wrist temperature (wT), light exposure (LE), and blue light exposure (BLE). Results — NA BLE exhibited clear seasonal variation, with a peak in spring and a nadir in winter, showing consistent patterns across sexes and populations (irrespective of indigeneity). Larger NA BLE correlated positively with indicators of circadian robustness, including Circadian Function Index (CFI) (p<0.0001), PA (p=0.001), and Inter-Daily Stability (p=0.008). Conversely, smaller NA BLE was associated with later circadian timing markers such as L5 onset of PA and BLE (p<0.001), bedtime (p=0.007), and lower stability of non-parametric actigraphy measures. Conclusions — Larger NA BLE significantly correlates with enhanced circadian robustness and healthier circadian timing, demonstrating its value despite seasonal fluctuations. NA BLE reliably measures circadian light hygiene, unaffected by sex or population subgroup. These results validate its utility in Arctic settings and advocate for its broader application in light exposure assessments to advance public health.

Background — The COVID-19 pandemic disrupted sleep and circadian rhythms, but the specific effects of prior infection on the body’s response to light for circadian regulation remain unclear. This study builds on previous research examining COVID-19 status and susceptibility to daylight by investigating seasonal variations in light hygiene and sleep parameters among young adults. Methods — We enrolled 187 medical students (mean age, 19.03±1.63 years; 132 females) from Tyumen, Russia. Participants wore ActTrust2 actigraphy devices with RGB light sensors for 1 week in spring (April-May; n=95) or autumn (October-November; n=92). We quantified circadian light hygiene using parametric and nonparametric measures, along with the normalized circadian amplitude of blue light exposure (NA BLE). Participants were grouped by COVID-19 infection history. We analyzed data with multiple linear regression and two-way ANOVA. Results — COVID-19-negative individuals had significantly higher daytime light exposure than COVID-19-positive individuals. Season and NA BLE were significant predictors of sleep parameters, with spring associated with shorter sleep duration and earlier bedtime compared with autumn. Higher NA BLE correlated with longer sleep duration, earlier bedtime, and greater relative amplitude of activity. Two-way ANOVA showed significant interactions between COVID-19 status and NA BLE for bedtime (p=0.021) and total sleep duration (p=0.019). These results indicate that prior COVID-19 infection modulates the association between light hygiene and sleep timing. Conclusions — Prior COVID-19 infection is linked to reduced daylight exposure and alters circadian sensitivity to light, affecting sleep timing and quality in young adults. These findings support considering COVID-19 history when developing light-based circadian interventions.