Characterization of β-cell function and insulin resistance in overweight Chinese adolescents with normal glucose tolerance

Abstract

This study aimed to investigate the characteristics of insulin resistance and β-cell secretion in healthy adolescents. A total of 124 adolescents with normal glucose tolerance (NGT) were divided according to BMI into normal weight (n=31; control), overweight (n=52) and obese (n=41) groups. Oral glucose tolerance tests were performed, and blood glucose (G₀, G₃₀ and G₁₂₀) and insulin (I₀, I₃₀ and I₁₂₀) levels at 0, 30 and 120 min, respectively, were measured. The homeostasis model assessment estimate of insulin resistance (HOMA-IR) and early insulin release index (IRI) were calculated to evaluate insulin sensitivity and early β-cell secretion. The G₀, G₁₂₀ levels and the natural logarithm (Ln) of I₃₀ and ΔI₃₀/ΔG₃₀ were similar in the overweight and obese groups, but significantly higher compared with those of the normal weight group (P<0.05). LnI₀ and LnHOMA-IR progressively increased (P<0.01) in correlation with the degree of obesity among the three groups. LnΔI₃₀/ΔG₃₀ and LnHOMA-IR were significantly positively correlated with the indices of obesity (P<0.001 and P<0.05, respectively). LnHOMA-IR was also positively correlated with the insulin levels at 30 and 120 min (r=0.454 and 0.314, respectively; P<0.001). In healthy adolescents, insulin resistance progressively increased with increased body mass index (BMI), but the compensatory increase in early insulin secretion was limited.

Keywords: adolescent; insulin resistance; islet cell; overweight; secretion.

Figure 1.

Comparisons of blood glucose and natural logarithm (Ln) of insulin levels among the three groups. (A) Comparison of blood glucose levels at fasting, 30 and 120 min (G₀, G₃₀ and G₁₂₀, respectively) via separate oral glucose tolerance tests among the three groups: NW, normal weight group; OW, overweight group; OB, obese group. (B) Comparison of Ln of blood insulin levels at fasting, 30 and 120 min (LnI₀, LnI₃₀ and LnI₁₂₀, respectively) via separate oral glucose tolerance tests among the three groups: NW, normal weight group; OW, overweight group; OB, obese group. ^*P<0.05, ^#P<0.01.

Figure 2.

Correlation analyses between variables in OGTT and BMI. Correlation analyses between BMI and (A) fasting glucose, (B) glucose at 120 min in the OGTT, (C) fasting serum insulin level and insulin levels at (D) 30 min and (E) 120 min in the OGTT. r, correlation coefficient; OGTT, oral glucose tolerance test; BMI, body mass index.

Figure 3.

Comparisons of IRI and HOMA-IR among the three groups. (A) Comparison of natural logarithm (Ln) of ΔI₃₀/ΔG₃₀ among the three groups: NW, normal weight group; OW, overweight group; OB, obese group. (B) Comparison of Ln of HOMA-IR among the three groups: NW, normal weight group; OW, overweight group; OB, obese group. ^*P<0.05, ^#P<0.01. IRI, insulin release index; HOMA-IR, homeostasis model assessment estimate of insulin resistance; ΔI₃₀/ΔG₃₀=(I₃₀−I₀)/(G₃₀−G₀); I₀, fasting insulin level; I₃₀, insulin level at 30 min; G₀, fasting glucose level; G₃₀, glucose level at 30 min.

Figure 4.

Correlation analyses between variables and HOMA-IR, as well ΔI₃₀/ΔG₃₀ (IRI). Correlation analyses between LnIRI and (A) BMI, (B) percentage of body fat and (C) percentage of truncal fat. Correlation analyses between HOMA-IR and (D) BMI, (E) percentage of body fat and (F) percentage of truncal fat. r, correlation coefficient; HOMA-IR, I₀ (μU/ml) × G₀ (mmol/l)/22.5; ΔI₃₀/ΔG₃₀=(I₃₀−I₀)/(G₃₀−G₀); I₀, fasting insulin level; I₃₀, insulin level at 30 min; G₀, fasting glucose level; G₃₀, glucose level at 30 min; IRI, insulin release index; Ln, natural logarithm; BMI, body mass index.