Characteristics of the salivary alpha‐amylase level in resting sublingual saliva as an index of psychological stress

The salivary alpha‐amylase (sAA) level is widely considered a marker of psychological stress. For clinical applicability, its characteristics should be examined under normal conditions. The aims of this study were to investigate the circadian rhythm, daily variation in a week and sex difference of the sAA level in sublingual saliva under a resting condition, for which 6 individuals, 11 individuals and 30 age‐matched women and men, respectively, were enrolled. The individual sAA levels were measured once every hour from 10:00 to 16:00 (7 times/day); at 10:00 on Monday, Wednesday and Friday (thrice/week); and without any restriction in the respective experiments by using a hand‐held sAA monitor. Repeated‐measures analysis of variance and the Student's t‐test were used for statistical analyses (p < 0.05). No significant differences in the sAA levels were observed among the different times of the day (p = 0.311) or different days of the week (p = 0.291), nor was a significant sex difference found (p = 0.962). These results suggest that the sAA level in sublingual saliva remains relatively stable under normal conditions and is not influenced by gender. It would be a useful tool to evaluate the effect of psychological stress in the clinical setting.