Screen Use and Emotional, Behavioral, and Social Development in Children.

Insulin sensitivity exhibits a diurnal rhythm and decreases over the day [, ]. In line with this, Kessler et al. [] showed an increase in insulin resistance if most carbohydrates (CHO) were consumed in the evening compared to morning intake. Regarding the prevention of Type 2 Diabetes (T2D) also CHO quality, i.e. dietary glycemic index (GI) [, ] or glycemic load (GL) are discussed. Current evidence, albeit preliminary, suggests that health benefits regarding T2D risk may particularly arise from the avoidance of large amounts of higher-GI-CHO (GI ≥ 55) consumed in the evening. This finding was reported earlier for the prospective association between CHO exposure during adolescence and T2D risk markers in adulthood [] and in an adult population of six shift workers within a randomized controlled trial []. Hence, the circadian intake of CHO and its quality may play an important role in the prevention of T2D. Focusing on adolescents is of tremendous importance as this age may constitute a vulnerable time window for the development of chronic diseases e.g. T2D []. Reasons may relate to a transient insulin resistance [], a delayed mid-point of sleep (i.e. late chronotype), which in turn may increase the risk of overweight [] and unfavorable body compositional developments during adolescence []. The chronotype describes individual differences in sleep timing (earlier or later), and is determined by genetics, age, sex, and environment []. Chronotype is primarily governed by the internal biological clock (circadian rhythm), located in the suprachiasmatic nucleus (SCN) of the hypothalamus, which is strongly influenced by light exposure. Sunlight acts as the most important external cue (or “Zeitgeber”) for aligning the internal clock with the 24-h day []. But also, the timing of food intake acts as a Zeitgeber and could potentially influence the balance between the internal and external clock. Later chronotypes have an increased T2D risk [], which may be explained via unfavorable body compositional developments [] and glycemic responses []. In a recent randomized controlled cross-over trial, we found that university students with early and late chronotypes exhibit different 2-h glucose responses to a high glycemic index meal, depending on whether the meal was consumed in the morning or evening []. Hence, the influence of CHO intake or quality on T2D risk may depend on timing of food intake and chronotype as hypothesized earlier [, ]. To the best of our knowledge the association between diurnal CHO intake during adolescence and adult T2D risk under consideration of chronotype remains unstudied. Given the elevated risk profile of adolescents for developing T2D, we aimed to investigate the long-term association between adolescent meal timing focusing on CHO intake (quantity and quality) as an early-life exposure that may influence later metabolic risk through long-term circadian and metabolic programming. Homeostasis model assessment 2—insulin resistance (HOMA2-IR), hepatic steatosis index (HIS), fatty liver index (FLI) [] and biomarkers of subclinical inflammation are established T2D risk factors in adulthood []. We hypothesized that the associations between diurnal CHO intake (quantity and quality) and diabetes risk factors differ by chronotype, meaning adolescents with an earlier chronotype may benefit most by consuming CHO earlier in the day (before 11 a.m.) while adolescents with a later chronotype may not. We further hypothesized that CHO quality, specifically glycemic index (GI), also modifies these associations, such that higher-GI CHO intake may be particularly important for adolescents with earlier chronotypes than for those with later chronotypes. The DONALD study is an ongoing dynamic (open) cohort study in which information on nutrition, growth, development and metabolism of healthy children and adolescents in Dortmund (Germany) is collected. The study was initiated in 1985 as a cross-sectional sample of children and adolescents. Ever since 35–40 infants were newly recruited each year. Eligibility criteria are healthy infants with willing parents to participate in a long-term study and at least one parent with sufficient knowledge of the German language. Invitations for examinations during adolescence take place annually including 3-day weighed dietary records, anthropometric measurements, 24-h urine samples, lifestyle interviews and medical examinations. Parental examinations take place every 4 years. The study is non-invasive during childhood and adolescence. Since 2005, participants aged ≥ 18 years have been invited for subsequent examinations including fasting blood samples collections. Further details of the study have been described elsewhere [, ]. The DONALD study is registered as a cohort study in the German Register of Clinical Trials (DRKS-ID: DRKS00029092). At the time of data preparation for this analysis (July 2019) the DONALD study sample consisted of N = 2,376 participants. Of these, blood sam