BOSTON (FRONTLINE MEDICAL NEWS) – Late chronotype may have a deleterious impact on glucose homeostasis independent of obesity in preadolescents aged 10-13 years, according to a small study.

Late chronotype – or an individual’s preference for later sleep and food intake – is associated with higher body mass index (BMI), risk incidence of type 2 diabetes mellitus, hemoglobin A1c, and risk of hypertension in adults. It is also associated with higher BMI, lower dietary restraint, and lower HDL cholesterol in adolescents. This study was the first to focus on chronotype and glycemic control in children on the cusp of or in early puberty.

In participants tested during the summer months, the actigraphy-derived mid-sleep time on free days – an objective measure of chronotype – was associated positively with fasting plasma glucose (P = 0.048). “This is an important point because it highlights the objective measure of chronotype, whereas questionnaires can be more subjective,” said Magdalena Dumin, MD , at the annual meeting of Associated Professional Sleep Societies.

An additional finding included HbA1c having been positively associated with late chronotype questionnaire scores. This suggested “that a later chronotype has an adverse effect on glucose homeostasis,” reported Dr. Dumin, who was one of the investigators in this study and is a pediatric endocrinologist at the University of Chicago Medical Center. Furthermore, higher Children’s ChronoType Questionnaire scores (a more subjective indicator of eveningness) tended to be associated with higher plasma glucose.

The researcher also noted that higher sleep fragmentation and lower sleep efficiency were both associated with hyperglycemia and hyperinsulinemia, independent of obesity.

“Our preliminary findings suggest that having a late chronotype and less efficient and more fragmented sleep in pre- and early adolescence may have a deleterious glycemic impact independent of obesity and pubertal stage,” she said.

“Advancing bedtimes may reduce glucose levels in preadolescents and adolescents,” Dr. Dumin surmised.

This study included 24 adolescents, 13 of whom were normal weight and 11 of whom were obese. They all underwent anthropometric measurements with fasting glucose, insulin, C-peptide, HbA1c, and lipid levels. Exclusion criteria included a clinical diagnosis of sleep, behavioral, or dietary problems. The obese subjects also underwent a 180-minute glucose tolerance test.

Chronotype was assessed via actigraphy over 1 week to provide mid-sleep time on free days, and secondarily through administration to chronotype questionnaires – the Children’s ChronoType Questionnaire and the Morningness-Eveningness Scale for Children.

Among the normal-weight participants, 31% were morning and 23% evening chronotype (the rest being neutral chronotype), and, in the obese subjects, 27% were morning and 36% were evening chronotype.

The obese subjects were more likely to be in puberty, and had higher systolic blood pressures, higher fasting plasma insulin and levels of insulin resistance, as measured by Homeostatic Model Assessment of Insulin Resistance. Hemoglobin A1c tended to be higher in the obese subjects (P = .06), but fasting plasma glucose did not differ significantly between the obese and normal-weight participants (P = .68).

“We chose this population due to the shift from morningness to eveningness that occurs during adolescence followed by a progressive return to an intermediate or early chronotype at the end of adolescence,” Dr. Dumin said.

Bedtime, wake time, and total sleep time were nearly identical between the two groups (7.84 hours and 7.62 hours; P = .49), although sleep efficiency was numerically lower in the obese subjects (87.0 vs. 89.8; P = .14), while sleep fragmentation was somewhat greater (20.16 vs. 17.38; P = .18).

Dr. Dumin suggested that a continuation of her research with more patients would be useful.

This study is supported by the Endocrine Fellows Foundation and the University of Chicago Institute of Translational Medicine. Dr. Dumin reported having no financial disclosures.


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