Habitual light exposure and circadian activity rhythms in bipolar disorder: A cross-sectional analysis of the APPLE cohort

Personal 24-hour light exposure pattern with obesity and adiposity-related parameters in school-aged children: A cross-sectional study based on compositional data analysis

The 24-h light exposure pattern is an essential feature of circadian rhythms and a potential contributor to body fat health. However, no previous studies have investigated 24-h light exposure patterns in relation to adiposity-related parameters in children. This cross-sectional study recruited school-aged children in Chuzhou, Anhui province, China. Personal 24-h light exposure was collected for 5 days and was divided into four measures: light at daytime (LAD)≥100 lx and <100 lx; light at night (LAN)≥1 lx and <1 lx. Adiposity-related parameters were measured via a body composition analyzer. The association of light exposure with adiposity-related parameters was analyzed using compositional data analysis (CoDA). This study included 831 children 8.53 ± 0.62 years, who were exposed to LAD≥100 lx for 490.1 ± 92.7 min and LAN≥1 lx for 311.2 ± 98.5 min. The proportion of time spent in LAD≥100 lx increasing by 1 % (14.4 min/day) was linked to a decline of 3.10 % in percentage of body fat (PBF). In contrast, prolonged exposure to LAN≥1 lx by 14.4 min/day was associated with an increase of 3.49 % in PBF (All P < 0.01). These associations were robust in boys after gender stratification. CoDA estimated that reducing the time of LAN≥1 lx had more influence in decreasing the odds of childhood overweight/obesity than increasing the time of LAD≥100 lx. Suboptimal 24-h light exposure patterns (brighter nights, darker days) play a threatening role in childhood overweight/obesity. Bright LAN replaced with darker LAN or bright LAD might help decrease the odds of childhood overweight/obesity.

Characterizing Architectural Glazing Performance for Circadian Light

Growing research on the non-visual impacts of light underscores the importance of architectural glazing systems in managing transmitted shortwave solar light and shaping indoor circadian light, vital for enhancing well-being. This study, conducted in two phases, evaluates the effectiveness of existing window properties in predicting their contribution to circadian lighting. Initially, a decision tree analysis assessed these properties and revealed that although traditional glazing metrics are not entirely accurate for circadian performance estimations, they can still be effective when supplemented with specific thresholds as rapid tools for selecting windows optimized for circadian health. The second phase introduced 'circadian transmittance' (Tc), a new metric measuring window transmittance tailored to the human circadian action spectra. Various machine-learning models were applied to assess the efficacy of Tc and other glazing properties in predicting these systems' circadian lighting potential. The analysis demonstrated that Tc-based methods yield more accurate predictions under conditions of high solar angles and clear skies, but their accuracy decreases in cloudy conditions and at low solar angles. In conclusion, this research significantly advances the field by proposing an analytical framework that empowers architects and engineers to make informed decisions to enhance indoor environmental health. The development of circadian transmittance-based machine learning models not only provides crucial insights into the impact of glazing properties on window systems' circadian performance but also sets the stage for future standards in fenestration's circadian metrics. These contributions are poised to influence building design and occupant health, marking a substantial step forward in environmental and architectural science.

The bright and dark side of blue-enriched light on sleep and activity in older adults

Low indoor light in urban housing can disrupt health and wellbeing, especially in older adults who experience reduced light sensitivity and sleep/circadian disruptions with natural aging. While controlled studies suggest that enhancing indoor lighting may alleviate the negative effects of reduced light sensitivity, evidence for this to be effective in the real world is lacking. This study investigates the effects of two light conditions on actigraphic rest-activity rhythms and subjective sleep in healthy older adults (≥ 60 years) living at home. Two photon-matched lights were compared; a control white light (4000 K) and a blue-enriched white light (17000 K) at two different intensities (300-450 lx and 1100-1200 lx respectively). Participants (n = 36, 25 female) completed an 11-week randomized, cross-over study, comprising 1 week of baseline, 3 weeks of self-administered light exposure (2 h in the morning and 2 h in the evening), and 2 weeks of washout for each light condition. Participants completed sleep diaries, wore a wrist actigraph and a light sensor necklace, and collected urine to measure 6-sulphatoxymelatonin. Longer duration of morning blue-enriched light significantly improved rest-activity rhythm stability and decreased sleep fragmentation. More time spent above 2500 lx increased actigraphy amplitude, daytime activity, and advanced bedtime. Evening light exposure, however, increased sleep latency and lowered sleep efficiency. Our findings show morning blue-enriched light is beneficial whereas evening light should be avoided. Optimal timing of self-administered light interventions thus may offer a promising strategy to improve sleep and rest-activity rhythms in older adults in real-world settings.

Seasonality in regional brain glucose metabolism

BACKGROUND

Daylength and the rates of changes in daylength have been associated with seasonal fluctuations in psychiatric symptoms and in cognition and mood in healthy adults. However, variations in human brain glucose metabolism in concordance with seasonal changes remain under explored.

METHODS

In this cross-sectional study, we examined seasonal effects on brain glucose metabolism, which we measured using 18F-fluorodeoxyglucose-PET in 97 healthy participants. To maximize the sensitivity of regional effects, we computed relative metabolic measures by normalizing the regional measures to white matter metabolism. Additionally, we explored the role of rest-activity rhythms/sleep-wake activity measured with actigraphy in the seasonal variations of regional brain metabolic activity.

RESULTS

We found that seasonal variations of cerebral glucose metabolism differed across brain regions. Glucose metabolism in prefrontal regions increased with longer daylength and with greater day-to-day increases in daylength. The cuneus and olfactory bulb had the maximum and minimum metabolic values around the summer and winter solstice respectively (positively associated with daylength), whereas the temporal lobe, brainstem, and postcentral cortex showed maximum and minimum metabolic values around the spring and autumn equinoxes, respectively (positively associated with faster daylength gain). Longer daylength was associated with greater amplitude and robustness of diurnal activity rhythms suggesting circadian involvement.

CONCLUSIONS

The current findings advance our knowledge of seasonal patterns in a key indicator of brain function relevant for mood and cognition. These data could inform treatment interventions for psychiatric symptoms that peak at specific times of the year.

A systematic literature review: building window's influence on indoor circadian health

Light has been shown to have a non-visual impact on the biological aspects of human health, particularly on circadian rhythms. Building windows are a potential means of regulating daylight conditions for circadian health and well-being. As a result of advancements in window and glazing technologies and variations in outdoor solar/sky conditions, understanding daylight's spectral characteristics, which pass through building window systems, is complex. Therefore, a systematic review and summary of the knowledge and evidence available regarding windows' impact on human circadian health is necessary. This study provides an overview of research in this domain, compares approaches and evaluation metrics, and underscores the importance of window parameters' influence on circadian health. Published studies available on various online databases since 2012 were evaluated. The findings of this study define a holistic approach to the melanopic performance of windows and provide an overview of current knowledge regarding the effect of windows on circadian health. Additionally, this work identifies future research directions based on the studies reviewed. This research contributes to the growing body of knowledge on the impact of windows on circadian health, which has implications for the design and construction of buildings in ways that support indoor human health and well-being from the circadian light adequacy perspective.