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Impact of Fatness, Fitness, and Ethnicity on the Relationship of Nocturnal Ghrelin to 24-Hour Luteinizing Hormone Concentrations in Adolescent Girls

Department of Pediatrics (J.Z.K.-V., A.R., E.G.M.), and Center for Statistical Consultation and Research (K.B.W.), University of Michigan, Ann Arbor, Michigan 48109

Address all correspondence and requests for reprints to: Josephine Z. Kasa-Vubu, M.D, M.S., Department of Pediatrics, University ofMichigan Medical Center, Ann Arbor, Michigan 48019-0718. E-mail: jzkv{at}umich.edu.

Context: Ghrelin is related to energy balance that regulates food intake.

Objective: The aim was to explore whether ghrelin would be linked to differences in fitness in adolescent girls, whose menstrual cycles are sensitive to changes in energy balance.

Methods: A total of 72 girls, ages 14–21 yr, including five with amenorrhea, were studied in the follicular phase. LH was sampled every 10 min over 24-h, and ghrelin was measured hourly between 2300 and 0300 h. Body composition was measured by dual x-ray absorptiometry. Fitness was characterized by reported frequency of exercise per week and by maximal oxygen consumption with "high" vs. "low" fitness groups defined from maximal oxygen consumption norms for this population. Data were analyzed with SAS software (SAS Institute Inc., Cary, NC).

Results: Ghrelin was related to percent body fat (P = 0.038; R² 0.07), weekly exercise (P = 0.032; R² 0.07), and 24-h mean LH (P = 0.002; R² 0.13). The ghrelin relationship with LH was more pronounced in the low-fitness group. In multiple regression models, 24-h LH was an independent predictor of ghrelin after adjusting for percent body fat, fitness, exercise, or age. Ghrelin was higher in Caucasian girls than in African-American girls after adjusting for covariates at 0200 h (P = 0.017).

Conclusions: Twenty-four-hour LH is an independent predictor of nighttime ghrelin concentrations in postpubertal adolescent girls. Diverging patterns in ghrelin may reflect differences in exercise patterns and/or may be influenced by ethnicity. These data introduce ghrelin as a biomarker of individual differences in energy balance during the menstrual cycle and across ethnicities.