Preliminary evaluation of dim light melatonin onset as an indicator of nighttime eating in adolescents.

Late sleep timing is associated with adverse eating and weight outcomes in adolescents. One possible behavioral mechanism may be nighttime eating: eating when melatonin levels are high disrupts glucose tolerance. Thus, we propose defining nighttime eating as eating after the onset of melatonin secretion (i.e., after the start of biological night). This exploratory study aimed to 1) validate use of an objective circadian marker of the start of biological night, dim light melatonin onset (DLMO), to define nighttime eating (eating before vs. after DLMO) and 2) examine whether nighttime eating is associated with metabolic markers. Adolescents (N = 68; 16-18y) completed one-week of actigraphy and one 24-h dietary recall in their natural environment during an observational phase. During a weeknight overnight laboratory visit, adolescents completed one assessment of DLMO via repeated saliva sampling. Adolescents were categorized according to the timing of their last naturalistic eating episode (on prior day) before (n = 48) vs. after DLMO (n = 20) and were compared on naturalistic dietary intake, physical activity, and BMI percentile using two-sample t-tests. Effect sizes are reported. Adolescents who ate after DLMO had greater total naturalistic caloric intake (d = 0.40), as well as lower BMI percentiles (d = 0.47) which may, in part, be explained by their higher levels of naturalistic weekly physical activity (d = 0.68). Future research should replicate these findings in larger samples and across multiple samplings of DLMO and dietary intake. Using DLMO to define nighttime eating may support future mechanistic research on excess energy intake/poor diet quality in adolescents. 244/250.