Circadian fluctuations in saliva biochemical composition: A pilot study

Saliva serves as a valuable, non-invasive diagnostic tool, yet the influence of circadian rhythms on its biochemical composition remains unclear. This study evaluated circadian fluctuations in unstimulated whole saliva, focusing on pH, total protein, glucose, and organic and inorganic ions. Eight healthy, caries-free adults provided unstimulated saliva samples at six time points (7:00 AM, 11:00 AM, 3:00 PM, 7:00 PM, 11:00 PM, and 3:00 AM) across a 24-hour period, on three separate days. Participants followed a standardized Mediterranean diet for three days before and during sampling. Saliva was analyzed for pH, total protein (bicinchoninic acid assay), and various biochemical markers using a calibrated reflectometer. Statistical analyses were performed using repeated measures ANOVA (p <0.05). No significant circadian variations were observed for calcium, phosphate, peroxide, salivary pH, or total protein (p >0.05). However, lactate, nitrate, nitrite, ammonium, and glucose exhibited significant circadian fluctuations (p <0.05), with distinct peaks at specific times. Circadian rhythm had a limited impact on the overall biochemical profile of unstimulated saliva in young, healthy adults. However, specific analytes exhibited significant fluctuations, highlighting the need for standardized sampling protocols in saliva-based diagnostics. Understanding circadian influences on saliva composition may improve the reliability of saliva as a diagnostic biofluid for oral and systemic conditions.

唾液是一种极具价值的非侵入性诊断工具，但目前关于昼夜节律（circadian rhythms）对其生化组成的影响仍尚未明确。本研究针对未刺激全唾液（unstimulated whole saliva）的昼夜节律波动展开评估，重点关注pH值、总蛋白、葡萄糖以及各类有机与无机离子。8名健康无龋（caries-free）成年人分别在3个独立日期的24小时周期内，于6个时间点（上午7:00、上午11:00、下午3:00、下午7:00、晚上11:00以及凌晨3:00）采集未刺激全唾液样本。受试者在采样前3天及采样期间均遵循标准化地中海饮食（Mediterranean diet）。采用校准后的反射光度计对唾液的pH值、总蛋白（采用二喹啉甲酸（bicinchoninic acid, BCA）法检测）以及各类生化标志物进行分析。统计学分析采用重复测量方差分析（repeated measures ANOVA）完成，检验水准设定为p<0.05。钙、磷酸盐、过氧化物、唾液pH值以及总蛋白未观察到显著的昼夜节律波动（p>0.05）。然而乳酸、硝酸盐、亚硝酸盐、铵离子以及葡萄糖则呈现出显著的昼夜节律波动（p<0.05），且在特定时间点出现明显峰值。对于年轻健康成年人而言，昼夜节律对未刺激全唾液的整体生化特征谱仅存在有限影响。但部分特定分析物却存在显著波动，这凸显了基于唾液的诊断检测中采用标准化采样流程的必要性。明确昼夜节律对唾液成分的影响，或可提升唾液作为口腔及全身疾病诊断生物流体（biofluid）的可靠性。