Saliva

Numerous functions, new applications

With between 0.5 and 1.5 liters of this body fluid secreted per day, saliva clearly plays a critical, multifaceted role in human digestive, dental and immune health. Saliva is 99.5 percent water, with its relatively high viscosity a result of additional substances of many types, including:

• Mucus – Consisting primarily of glycoproteins and mucopolysaccharides
• Electrolytes – Including potassium, sodium, calcium, magnesium, chloride, bicarbonate, phosphate and iodine
• Epidermal growth factor (EGF) – a small polypeptide responsible for cellular proliferation and differentiation; salivary EGF helps support oroesophageal and gastric tissue health, and provides some mucosal protection against endogenous acids as well as other chemical or bacterial agents
• Antimicrobial enzymes and other compounds – Including hydrogen peroxide, thiocyanate, lysozyme, lactoferrin and immunoglobulin A
• Proline-rich proteins – Supportive of tooth enamel formation, calcium ion binding and lubrication
• Various digestive and other enzymes – Enzyme α-amylase initiates starch pre-digestion; lingual lipase is activated upon being swallowed and reaching the stomach; kallikrein helps produce bradykinin, a vasodilator
• Opiorphin – An endogenous painkilling compound discovered in 2006

Saliva also contains a significant cellular component, with bacterial cells outnumbering human cells by a more than 60-to-1 ratio; each milliliter of saliva may contain 8 million human cells and as many as 500 million bacterial cells.

Genetics and identification

Because of the high number of human cells it contains, saliva has emerged this century as a highly reliable, easily collected source of genetic and other identifying material. DNA and serological substances isolated from cells in saliva can be readily sampled, prepared, analyzed and/or sequenced to reveal vast amounts of information about the person from whom the sample was collected. This has paved the way for advancements in multiple fields and industries, most notably:

• Forensic sciences – Analysis of saliva has become a well-established tool for various applications, including:
  • Crime detection
  • Substance abuse detection
  • Hormone identification
  • Characterization of poisoning and animal bites
• Genealogical research – DNA derived from white blood cells and buccal epithelial cells in the mouth via cheek swab can be obtained at high quality in relatively large quantities — as much per unit volume as a blood sample; private companies now regularly supply saliva collection kits for at-home sampling and subsequent ancestry analysis.