Obesity is a common disorder with many complications. Although chronodisruption plays a role in obesity, few epidemiological studies have investigated the association between artificial light at night (ALAN) and obesity. Since sleep health is related to both obesity and ALAN, we investigated the association between outdoor ALAN and obesity after adjusting for sleep health. We also investigated the association between outdoor ALAN and sleep health. This cross-sectional survey included 8526 adults, 39–70 years of age, who participated in the Korean Genome and Epidemiology Study. Outdoor ALAN data were obtained from satellite images provided by the US Defense Meteorological Satellite Program. We obtained individual data regarding outdoor ALAN; body mass index; depression; and sleep health including sleep duration, mid-sleep time, and insomnia; and other demographic data including age, sex, educational level, type of residential building, monthly household income, alcohol consumption, smoking status and consumption of caffeine or alcohol before sleep. A logistic regression model was used to investigate the association between outdoor ALAN and obesity. The prevalence of obesity differed significantly according to sex (women 47% versus men 39%, p < 0.001) and outdoor ALAN (high 55% versus low 40%, p < 0.001). Univariate logistic regression analysis revealed a significant association between high outdoor ALAN and obesity (odds ratio [OR] 1.24, 95% confidence interval [CI] 1.14–1.35, p < 0.001). Furthermore, multivariate logistic regression analyses showed that high outdoor ALAN was significantly associated with obesity after adjusting for age and sex (OR 1.25, 95% CI 1.14–1.37, p < 0.001) and even after controlling for various other confounding factors including age, sex, educational level, type of residential building, monthly household income, alcohol consumption, smoking, consumption of caffeine or alcohol before sleep, delayed sleep pattern, short sleep duration and habitual snoring (OR 1.20, 95% CI 1.06–1.36, p = 0.003). The findings of our study provide epidemiological evidence that outdoor ALAN is significantly related to obesity.

Bisphenol A (BPA) is an environmental chemical that has adverse effects on health, probably causing childhood obesity. However, this association remains controversial, and it is difficult to find evidence for direct causality between environmental exposure and disease using epidemiological studies. In this study, we sought to elucidate the possible causality between BPA exposure and childhood obesity by conducting two meta-analyses showing bidirectional associations, including exposure effect by obesity and obesity risk by exposure. Articles published up to September 2017 were searched in PubMed, Embase, and Cochrane Library. We evaluated observational studies that included measurements of urinary BPA concentration and BMI or body weight. Of 436 articles, a total of 13 studies were included in the meta-analysis. Two meta-analyses were performed to investigate the association between BPA exposure and childhood obesity. The results showed that the relatively high-exposed group had a significantly higher risk of childhood obesity than the relatively low-exposed group (odds ratio = 1.566, 95% confidence interval [CI]: 1.097 to 2.234, p = 0.014). However, the obese group showed no significant difference in the BPA concentration when compared to the normal group (standardized mean difference = 0.166, 95% CI: −0.121 to 0.453, p = 0.257). This study suggested possible causality between BPA exposure and childhood obesity using data from epidemiological studies and showed that BPA exposure itself increased the risk of obesity in children.

The Comet assay has gained increasing popularity for use in human biomonitoring or epidemiologic studies; however, one of the shortcomings of the Comet assay is a lack of agreement on a single appropriate Comet parameter that is capable of adequately describing observed DNA damages. Among the tail parameters of Comet features, the most frequently used are the tail moments (both the Olive tail moment and the extent tail moment), the tail DNA, and the tail length. Some studies comparing Comet parameters have been found in cell toxicity research, but there are few comparative studies that use human biomonitoring or epidemiologic data. In this study, we evaluate those four tail parameters in both high and low DNA damaged cells with the use of epidemiologic data. To do this, a new graphical approach, the so-called quantile dispersion graphs (QDGs) are used. In a comparison of an exposed group and a control group, either the tail moment or tail DNA is preferable to the tail length. With respect to providing smaller variability in quantiles for the amount of DNA damage, however, the tail moment is the preferred parameter for both groups. Moreover, the tail moment provides the most stable estimates for DNA damage because it has a larger degree of uniformity in quantile dispersions. To study high degrees of damage from toxic exposure using B cells or G cells, however, the tail DNA showed more significant discrepancies than the other parameters, in terms of both the mean differences and the graphical differences between the two groups. In view of this result, it is suggested that both the tail moment and the tail DNA be presented as tail parameters in human biomonitoring studies.

Exposure to artificial light at night (ALAN) has become increasing common, especially in developed countries. We investigated the effect of dALAN exposure during sleep in healthy young male subjects. A total of 30 healthy young male volunteers from 21 to 29 years old were recruited for the study. They were randomly divided into two groups depending on light intensity (Group A: 5 lux and Group B: 10 lux). After a quality control process, 23 healthy subjects were included in the study (Group A: 11 subjects, Group B: 12 subjects). Subjects underwent an NPSG session with no light (Night 1) followed by an NPSG session randomly assigned to two different dim light conditions (5 or 10 lux, dom λ: 501.4 nm) for a whole night (Night 2). We found significant sleep structural differences between Nights 1 and 2, but no difference between Groups A and B. Exposure to dALAN during sleep was significantly associated with increased wake time after sleep onset (WASO; F = 7.273, p = 0.014), increased Stage N1 (F = 4.524, p = 0.045), decreased Stage N2 (F = 9.49, p = 0.006), increased Stage R (F = 6.698, p = 0.017) and non-significantly decreased REM density (F = 4.102, p = 0.056). We found that dALAN during sleep affects sleep structure. Exposure to dALAN during sleep increases the frequency of arousals, amount of shallow sleep and amount of REM sleep. This suggests adverse effects of dALAN during sleep on sleep quality and suggests the need to avoid exposure to dALAN during sleep.

Seasonal affective disorder (SAD) is a condition of seasonal mood changes characterized by recurrent depression in autumn or winter that spontaneously remits in spring or summer. Evidence has suggested that circadian gene variants contribute to the pathogenesis of SAD. In this study, we investigated polymorphisms in the CLOCK, ARNTL, and NPAS2 genes in relation to seasonal variation in 507 healthy young adults. Seasonal variations were assessed with the Seasonality Pattern Assessment Questionnaire. The prevalence of SAD was 12.0% (winter-type 9.3%, summer-type 2.8%). No significant difference was found between the groups in the genotype distribution of ARNTL rs2278749 and NPAS2 rs2305160. The T allele of CLOCK rs1801260 was significantly more frequent in seasonals (SAD + subsyndromal SAD) compared with non-seasonals (p = 0.020, odds ratio = 1.89, 95% confidence interval = 1.09-3.27). Global seasonality score was significantly different among genotypes of CLOCK rs1801260, but not among genotypes of ARNTL rs2278749 and NPAS2 rs2305160. However, statistical difference was observed in the body weight and appetite subscales among genotypes of ARNTL rs2278749 and in the body weight subscale among genotypes of NPAS2 rs2305160. There was synergistic interaction between CLOCK rs1801260 and ARNTL rs2278749 on seasonality. To our knowledge, this study is the first to reveal an association between the CLOCK gene and seasonal variations in mood and behavior in the Korean population. Although we cannot confirm previous findings of an association between SAD and the ARNTL and NPAS2 genes, these genes may influence seasonal variations through metabolic factors such as body weight and appetite. The interaction of the CLOCK and ARNTL genes contributes to susceptibility for SAD.