The diurnal patterns of salivary interleukin-6 and C-reactive protein in healthy young adults

In recent years, salivary inflammatory markers, such as interleukin-6 (IL-6) and C-reactive protein (CRP), have been investigated regarding their relationships with psychosocial stress and stress-related diseases. This study investigated the diurnal patterns of salivary IL-6 and CRP in healthy young adults. Twenty-seven students (11 males and 16 females) participated in this study. The participants were instructed to provide saliva samples 8 times a day (at 0700, 0730, 1000, 1300, 1600, 1900, 2200, and 0100 h). For the duration of study, they were asked to wake up at 0700 h and go to bed after 0100 h. Twelve of the participants were asked to repeat this sampling procedure on two consecutive days to test the stability of the diurnal patterns. The salivary IL-6 levels peaked at awakening, gradually declined from morning to noon, and peaked again at midnight, before the participants went to sleep. The salivary CRP levels peaked at awakening, and they were lower during the daytime. The salivary IL-6 and CRP levels exhibited moderate to high stability over 2 days of sample collection. This study revealed that the salivary inflammatory markers had distinctive diurnal patterns.

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► This study indicates that salivary levels of IL-6 and CRP are more variable in the morning and at night.