The aim of this study was to investigate physiological factors that affect serum insulin levels and to establish insulin reference intervals for healthy Chinese Han adults. A total of 4401 subjects with normal glucose tolerance (NGT) were screened from 10,027 individuals in an epidemiological study. Based on the exclusion criteria, 2414 apparently healthy adults (healthy) were selected as reference individuals. Serum insulin levels of the reference individuals were measured at fasting, 30 min and 120 min after oral glucose tolerance test (OGTT). Significant correlations were found between serum insulin levels and physiological factors in healthy subjects, including body mass index (BMI), weight, systolic blood pressure (SBP), diastolic blood pressure (DBP), etc. (p < 0.05). No increase or decrease was found in age-dependent insulin levels by ANOVA (p > 0.05). There was also no substantial difference in fasting serum insulin levels between males and females (p > 0.05). However, we detected notable differences in serum insulin levels between males and females at 30 min (p < 0.01), which became more pronounced at 120 min (p < 0.001). According to our data, BMI/gender-related insulin reference intervals were defined by calculating 2.5th and 97.5th percentiles. The insulin reference intervals, determined after assessing the relationship between physiological factors and serum insulin levels in Chinese adults, will provide valuable information for physicians in their interpretation of insulin levels.
Keywords: China; Diabetes mellitus; body mass index; epidemiological studies; reference values.