Saliva Is a Critical but Underestimated Bodily Fluid
Human life would be difficult to sustain without saliva. Its fundamental role in keeping the oral mucosa hydrated is essential for core functions such as swallowing, tasting, and speaking. However, recent research has revealed that saliva does far more than previously understood. Specific components may eventually serve as noninvasive biomarkers for a variety of diseases.
As with other bodily processes, the production and composition of saliva are regulated by intricate mechanisms under the control of the autonomic nervous system. The parasympathetic system stimulates the secretion of electrolytes and water via acetylcholine, while the sympathetic system regulates the release of salivary proteins through norepinephrine. External stimuli — such as smell, taste, and mastication — further influence both the volume and composition of saliva. For example, stimulated saliva contains significantly more bicarbonate but fewer proteins compared to resting saliva. Additional factors such as sex, age, time of day, medication use, and general health also affect salivary output and composition.
Mucosal Health
The moistening of the oral, pharyngeal, and esophageal mucosa is essential for several vital functions. In addition to hydration, saliva contains cytokines, chemokines, and growth factors that promote wound healing — often more rapidly than on skin. Among these, histatins are especially effective in accelerating tissue repair.
Saliva also plays a crucial role in innate immune defense. It contains a broad range of antimicrobial proteins and peptides — including myeloperoxidase, lysozyme, lactoferrin, and others — produced by salivary glands, oral epithelial cells, and immune cells, all of which contribute to protection against infection.
Saliva in Oral Health
In dentistry, saliva is particularly valued for its protective effect against dental caries. Bicarbonate and phosphate ions help buffer oral pH, maintaining a range between 6.8 and 7.8. Salivary proteins bind calcium and phosphate, forming a supersaturated solution that supports the dynamic balance of enamel demineralization and remineralization — critical processes for caries prevention.
Saliva also rapidly forms a thin protein-rich layer on tooth surfaces known as the acquired pellicle. This layer protects enamel against calcium loss, mechanical abrasion, and erosion. Over time, bacterial colonization of the pellicle also influences the composition of the oral microbiome.
Diagnostic Biomarkers
In recent years, research has increasingly focused on the potential of salivary components to serve as biomarkers for disease diagnosis. Compared with blood sampling, saliva collection offers clear advantages: it is easier, less invasive, and more cost-effective. These features make it particularly useful in populations such as children, older adults, and individuals with disabilities.
Saliva contains a wide range of biologically active substances — including enzymes, hormones, antibodies, cytokines, and DNA/RNA fragments — that can reflect both local and systemic physiological processes. These biomarkers are being studied in connection with conditions ranging from periodontal disease and diabetes to neurological, psychiatric, and oncologic disorders.
Glucose Levels in Saliva
In patients with diabetes mellitus, saliva can reveal metabolic changes, including glucose fluctuations, elevated HbA1c levels, and markers of oxidative stress. These salivary findings may also correlate with periodontal health status. Research has additionally identified alterations in lipid levels, melatonin, and total protein in the saliva of diabetic patients. In clinical dental settings, an unusual salivary profile may help flag cases of undiagnosed or poorly controlled diabetes — a condition known to increase the risk of periodontal disease. Timely, multidisciplinary management may therefore improve outcomes both systemically and dentally.
Cortisol and Other Stress Markers
Psychiatric conditions such as anxiety disorders, schizophrenia, and depression are also associated with measurable changes in salivary composition. Cortisol, a key biomarker of chronic stress, is frequently elevated in these populations. Altered levels of other markers, such as alpha-amylase and lysozyme, have also been detected in individuals with anxiety. These salivary biomarkers may provide insights into psychosomatic interactions and could support more comprehensive care strategies for patients with conditions such as bruxism or dental phobia.
Early Cancer Detection
Saliva has also shown promise in the early detection of malignancies, including both head and neck tumors and systemic cancers such as pancreatic and breast cancer. Tumor-associated biomarkers — such as specific antibodies, antigens, and gene mutations — can be identified in salivary samples. One molecule of particular interest is sialic acid, which is elevated in patients with certain cancers. In a recent study, Elgendi and colleagues presented a portable device capable of quantifying salivary sialic acid, yielding promising results for early breast cancer detection. This type of technology could potentially be used not only in oncology centers but also in primary care and dental practices.
Future Diagnostic Tool
These findings suggest that saliva analysis could play an important role in the future of diagnostic medicine. For dental professionals in particular, salivary diagnostics may offer a valuable tool for identifying high-risk patients, supporting clinical decision-making, and monitoring disease progression. In patients with periodontal disease, it may serve as a practical adjunct to traditional examination methods. The use of noninvasive, affordable rapid tests in everyday practice appears increasingly feasible — especially as integrated, interdisciplinary approaches to healthcare continue to gain importance.
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