INS and diabetes mellitus: Similar to our findings, Islam et al. [33] reported that participants with pre-diabetes had lower zinc levels than did normal participants in a cross-sectional study of 280 Bangladesh adults aged ≥30 years, and Vashum et al. [34] showed that a higher serum zinc concentration was associated with increased insulin sensitivity in a cross-sectional study of 452 Australian adults aged 55–85 years.