Abstract and Introduction
Abstract
Background Low serum amylase is likely to be associated with obesity and metabolic abnormalities, which are often accompanied by impaired insulin action. However, it is unclear whether low serum amylase is associated with impaired insulin action in clinical settings. Therefore, we investigated the associations of low serum amylase with plasma insulin levels, and obesity-related parameters, including leptin.
Research design and methods We measured serum amylase, plasma insulin, obesity-related parameters such as leptin, cardiometabolic risk factors, and anthropometric parameters in a cross-sectional study of 54 asymptomatic subjects (mean age 48.6 ± 7.6 years) who were not being treated for diabetes.
Results Body mass index (BMI) and plasma glucose at 120 min after a 75-g oral glucose tolerance test (OGTT) were significantly higher in subjects with low serum amylase (< 60 IU/l, n = 21) than in those with normal-to-high serum amylase (n = 33) (P = 0.04 and P = 0.004, respectively). In univariate correlation analysis, serum amylase was significantly correlated with BMI alone (r = –0.39, P = 0.004). By contrast, multivariate logistic analysis showed that each 1-SD increase in quantitative insulin sensitivity check index, and each 1-SD decrease in plasma insulin OGTT at 0 and 60 min, homeostasis model assessment of insulin resistance (HOMA)-R, and HOMA-β were significantly associated with low serum amylase, particularly after adjusting for BMI. When subjects were divided into three groups according to HOMA-R, serum amylase levels were significantly lower in subjects with HOMA-R > 2.5 (n = 23) compared with subjects with HOMA-R 1.6–2.5 (n = 10) (61.1 ± 13.6 U/ml versus 76.9 ± 20.5 U/ml, Bonferroni test, P = 0.02), but not compared with subjects with HOMA-R<1.6 (n = 21; 62.7 ± 17.6 U/ml). Similar trends were observed when subjects were divided according to plasma leptin and fasting plasma insulin levels.
Conclusions These results suggest that after adjusting for BMI, low serum amylase is associated with decreased basal insulin levels and insulin secretion, as well as high insulin resistance. The nature of these associations remains to be elucidated in further studies.
Introduction
For many years, low serum amylase was thought to reflect diffuse pancreatic destruction secondary to advanced pancreatic diseases, such as chronic pancreatitis. Recently, several large clinical studies have shown that low serum amylase is also associated with metabolic syndrome and diabetes. However, the mechanisms underlying these associations remain unclear. In previous epidemiological studies, we observed a marked negative association between serum amylase and body mass index (BMI). Consequently, we hypothesized that high BMI (i.e., obesity) is the most critical factor that is inversely correlated with serum amylase, and that insulin inactivity is a putative secondary factor that regulates the observed association. In our previous sub-analysis, we found that the relationship between serum amylase levels and glycated hemoglobin (HbA1c) was rather complicated (not a simple linear relationship), particularly in individuals with normal or mildly impaired glucose metabolism. Unfortunately, plasma insulin and obesity-related parameters, such as leptin and tumor necrosis factor (TNF) α, were not measured in the earlier studies. Therefore, we were unable to determine whether impaired insulin action, particularly insulin resistance, could mediate the associations between low serum amylase and diabetes and metabolic syndrome.
In this cross-sectional study of asymptomatic middle-aged subjects without advanced diabetes, plasma insulin and obesity-related parameters were measured along with other cardiometabolic risk factors. Here, we report latent associations between low serum amylase and plasma insulin, insulin resistance, and obesity-related parameters. Leptin, an adipokine that regulates energy balance through a wide range of systemic functions, is associated with obesity and insulin resistance. Additionally, TNFα, a proinflammatory adipokine, was proposed as a link between obesity and insulin resistance. Therefore, we also examined the associations between low serum amylase and these adipokines in this study.