Salivary Melatonin Concentrations in a Sitting and a Standing Position

This study aimed to examine differences in salivary melatonin concentrations between the sitting and standing positions. Ten subjects (age range: 20–22 years; 5 males and 5 females) participated in the study and provided written consent. In the sitting condition, the subjects sat on a chair from 23:30 h to 1:00 h, whereas in the standing condition, the subjects sat on a chair from 23:30 h to 0:30 h and stood on the floor from 0:30 h to 1:00 h. Saliva samples were obtained at 0:25 h and 1:00 h from all subjects. The experiment was performed under a dim light condition (<10 lx). No significant differences were observed in melatonin concentrations between the two positions at 0:25 h; however, melatonin concentrations in the standing condition were significantly greater than those in the sitting condition at 1:00 h. These results show that melatonin secretion is significantly greater in the standing position than that in the sitting position.