CIRCADIAN CORTISOL RHYTHMS IN HEALTHY BOYS AND GIRLS - RELATIONSHIP WITH AGE, GROWTH, BODY-COMPOSITION, AND PUBERTAL DEVELOPMENT

To provide basic information on the normal functioning of the hypothal amus-pituitary-adrenal axis in relation to pubertal development, growt h (weight and height), body composition, and gender and to obtain refe rence data for serum cortisol concentrations in children, we investiga ted the basal circadian rhythm of serum cortisol in a group of 235 hea lthy children (162 boys and 73 girls). The age range was between 2.2-1 8.5 yr. Serum cortisol was analyzed from venous blood samples taken at 1400, 1800, 2200, 0200, 0400, 0600, and 1000 h. No evidence was found for differences in temporal placement or level of the circadian corti sol rhythm in relation to age, growth, or body composition. However, w e found a broad range of cortisol levels in a healthy population, with individual mean diurnal ranging from 100-510 nmol/L. Regardless of hi gh or low mean diurnal cortisol levels, repeated measurements within a nd between pubertal stages indicated that an individual remains in his or her cortisol range throughout pubertal development. In conclusion, the present study shows that 1) serum cortisol levels do not correlat e with either age or gender; 2) there is a large and significant inter individual variability in endogenous mean diurnal cortisol levels; and 3) despite this variability between individuals, there is no correlat ion between cortisol levels and either body composition or growth rate . This suggests that the variability in cortisol levels is an expressi on of normal homeostasis rather than pathology.