Insulin, a core anabolic peptide hormone, is responsible for regulating the metabolism of nutrients such as glucose and fatty acids to promote their absorption into fat, liver, and skeletal muscle cells. It also suppresses the breakdown of proteins into amino acids. Circulating insulin levels stimulate cellular glucose oxidation, glycogenesis, lipogenesis, and proteogenesis to maintain glucose homeostasis and are mainly modulated by beta cells in the islets of Langerhans and hyperglycemic hormones such as cortisol, glucagon and growth hormones. Multiple systems, as well as metabolic and neural influences co-function to regulate insulin levels. Prolonged deficiencies in insulin regulation have been linked to a myriad of health risks, including metabolic syndrome, obesity, diabetes mellitus, water bloating, high blood pressure, endocrine dysfunctions and increased levels of inflammatory compounds in the blood.

In saliva, insulin shares a near linear correlation to fasting blood levels and is a reliable surrogate for serum measures, with a 0.92 correlation (Fabre 2012). During an oral glucose tolerance test, research shows a ~30 minute delay between salivary insulin and the spike in serum insulin levels (Fekete 1993). Overall, salivary insulin presents a unique opportunity to monitor insulin levels prior to disease progression. Elevated fasting insulin is a hallmark of insulin resistance, which can supersede TIID disease onset by several years and may be used to justify changes in lifestyle to reduce the risk of disease (Tomoshige Hayashi 2013).