Copy Number Variation of the Salivary Amylase Gene and Glucose Metabolism in Healthy Young Japanese Women.

Background: Many studies have shown that low copy number variation (CNV) of the salivary amylase gene () and low serum amylase concentration are associated with impaired glucose metabolism and obesity. We aimed to clarify the conflicting results of previous studies by examining expression and metabolic indices in a homogenous group of healthy participants.

Methods: Sixty healthy non-obese young Japanese women aged 20 - 39 years were examined for CNV, salivary amylase, body mass index (BMI) and serum parameters including glycated hemoglobin (HbA1c), ketones, and total, salivary and pancreatic amylase. Respiratory quotient at rest and changes in blood glucose after starch loading were also examined.

Results: CNV (range, 4 - 14) and the level of serum salivary amylase were correlated inversely with HbA1c (r = -0.36, P = 0.003 and r = -0.30, P = 0.02, respectively), whereas the percentage of serum salivary amylase in total serum amylase was positively correlated with blood glucose at 30 and 45 min after starch loading (r = 0.38, P = 0.004 and r = 0.27, P = 0.04, respectively). The level of serum total amylase, but not CNV, was correlated inversely with BMI (r = -0.29, P = 0.02). Logistic regression analysis showed that low CNV (4 - 7) was significantly associated with an HbA1c of ≥ 5.4% (34 mmol/mol) even after adjustment for age, BMI and energy consumption, compared with high CNV (8 - 14).

Conclusions: Although a higher percentage of serum salivary amylase was associated with higher levels of blood glucose at the early stage after starch loading, low CNV was associated with chronic unfavorable glucose metabolism in healthy non-obese young women in Japan.