Circadian Influence on Saliva Biochemical Composition: A Pilot Clinical Investigation

Objective. Saliva is a valuable non-invasive diagnostic tool, but the impact of circadian timing on its biochemical composition is not fully understood. We, therefore sought to investigate whether circadian fluctuations of unstimulated saliva affect biochemical parameters, including pH, total protein, glucose, and organic and inorganic ions. Materials and Methods . Eight healthy, caries-free young adults donated whole unstimulated saliva at six time-points throughout the day, with each participant providing samples on three separate days, ensuring triplicate collections for each time-point. Before saliva collection, participants adhered to a standardized Mediterranean diet for three days and during collection day. Collected saliva samples were analyzed for pH by a pH-meter, protein by bicinchoninic acid test, and glucose and ions using a calibrated reflectometer. Statistical comparisons across the different time-points were conducted using ANOVA repeated measures test (p<0.05). Results. The circadian rhythm did not result in statistical variations between-subjects on the measured time-points for calcium, phosphate, peroxide, salivary pH, or total proteins in unstimulated saliva (p>0.05). However, significant circadian variations were observed for lactate, nitrate, nitrite, glucose, and ammonium (p<0.05), with distinct peaks observed at specific times during the day. Conclusions. Circadian rhythm appears to have a limited impact on the overall biochemical composition of unstimulated saliva in young, healthy adults. Significant fluctuations in specific analytes warrant further investigation. Clinical Relevance: These findings may contribute to the standardization and refinement of research using saliva as a biomarker for oral and systemic conditions. The differences observed between volunteers highlight the individual diagnostics in the prevention of oral diseases.