Endocrine Abstracts

Introduction: Insulin requirements change with age, in part related to changes in Growth Hormone secretion. Little is known of the impact of age on the circadian variation in insulin secretion. We have studied changes in insulin basal rates as a proxy for insulin sensitivity in CYP with well controlled T1DM.

Methods: Insulin pump settings for total daily dose (TDD) and sensitivity ratio were obtained from 22 CYP with T1DM. Basal insulin requirements were calculated for four time blocks 0000–0600 h, 0600–1200 h, 1200–1800 h and 1800–2400 h. There were nine males/13 females aged 4–14.5 years. Height and weight data from the time of pump download were used to calculate BMI. Insulin settings were related to age, sex and BMI.

Results: TDD was 0.9 U/kg for males and 0.7 U/kg for females (P=0.03). There were no differences between the sexes for age, BMI or HbA1c. For every 1 year increase in age HbA1c declined by 0.13% (P=0.02). Sensitivity ratio was inversely related with age (r=−0.65; P=0.006) with no effect of sex or BMI. Total basal insulin increased with age.

The coefficient for this increase was highest (0.11) for the time period 0000–0600 h compared to the other time periods; 0600–1200 h (0.09), 1200–1800 h (0.05) and 1800–2400 h (0.08).

Discussion/conclusion: These data suggest that there is an age effect on the circadian variation in insulin sensitivity as reflected in basal insulin delivery rates. The change in insulin sensitivity decreases with age across the whole study population and is not influenced by sex or BMI. Although Growth Hormone has been implicated in the pubertal alterations these data would suggest that other factors, either intrinsic or extrinsic, may influence insulin sensitivity through childhood and adolescence.