Relationship between zinc and glucose metabolism in Japanese adults

Background: The association between decreased zinc and poor glycemic control has been revealed in diabetic patients. However, the involvement of zinc in glucose metabolism in healthy, non-diabetic individuals remains unclear. Methods: Company T employees and their spouses who underwent the milestone-age health checkups at the Tokyo Health Service Association were recruited in the study (n=533). The following variables were obtained from blood and urine samples and questionnaires: three zinc measures (serum zinc, urinary zinc, and zinc intake); two obesity-related measures (visceral fat and adiponectin); three insulin-related measures (insulin, HOMA-β, and HOMA-IR); and two glucose-related measures (fasting plasma glucose and HbA1c). Results: Correlation analysis between zinc measures revealed a significant correlation between serum zinc and urinary zinc, but not between the other pairs. Correlation analysis between zinc measures and obesity-, insulin-, and glucose-related measures revealed weak but significant correlations between serum zinc and adiponectin and HbA1c, as well as between urinary zinc and fasting plasma glucose and HbA1c. A path analysis using structural equation modeling confirmed that serum zinc was directly linked to urinary zinc and adiponectin, which affected blood glucose levels (HbA1c) directly and indirectly by influencing insulin secretion function (HOMA-β). Conclusion: This is the first study to statistically demonstrate the pathway linking zinc to blood glucose levels in healthy, non-diabetic adults using objective measurement data. Lower serum zinc levels were associated with lower adiponectin levels and lower insulin secretory function, resulting in higher blood glucose levels.