Circadian rhythms in human salivary flow rate and composition

Area of Science:

• Chronobiology
• Human Physiology
• Oral Medicine

Background:

• Circadian rhythms significantly influence various physiological processes.
• Saliva composition and flow rate are critical for oral health.
• Understanding daily variations in salivary parameters is essential.

Purpose of the Study:

• To investigate the presence and characteristics of circadian rhythms in human whole and parotid saliva.
• To analyze daily variations in salivary flow rate and electrolyte concentrations.
• To compare salivary circadian rhythms with oral temperature rhythms.

Main Methods:

• Collection of unstimulated whole saliva and stimulated parotid saliva from eight subjects over 4-26 days.
• Saliva samples collected at multiple time points throughout the day (07:00, 11:00, 14:00, 17:00, 22:00).
• Cosinor analysis used to assess circadian rhythms in salivary parameters and oral temperature.

Main Results:

• Significant circadian rhythms were observed in the flow rate and sodium and chloride concentrations of unstimulated whole saliva.
• Stimulated parotid saliva showed significant circadian rhythms in protein, sodium, potassium, calcium, and chloride concentrations.
• Oral temperature exhibited a clear circadian rhythm with a 24.0-hour periodicity, consistent with salivary rhythms.

Conclusions:

• Human salivary function, including flow rate and electrolyte balance, is subject to significant circadian regulation.
• These findings highlight the temporal organization of salivary physiology.
• The study demonstrates a parallel circadian rhythmicity between salivary parameters and oral temperature.