Salivary Oxytocin Levels Measurement

Saliva samples were collected using the Salivette^® cotton roll (Sarstedt, Nümbrecht, Germany) [25 (link),29 (link)] at around 5:00 AM on days 2, 5, 8, 13, 18, 20, 21, 22 and 30 (Table 1). To avoid contamination, the participants were instructed to refrain from consuming food and drinks other than water and from brushing teeth for 60 min and 10 min, respectively before sample collection. Collected samples were immediately stored in a freezer at −20 °C and sent to the National Center for Child Health and Development (Tokyo, Japan) at the end of the camp to be kept at −80 °C until analysis. OT concentrations were measured using a commercial ELISA kit (Assay Designs; Ann Arbor, MI, USA) and standardized by total protein content per milliliter and expressed in picograms per milligram protein (pg/mg protein) [28 (link)]. Missing information on height and weight (n = 1) was replaced with the average of three participants with the same age, and missing information on OT level on day 2 (n = 2) and day 18 (n = 2) was replaced with subsequently measured OT level of the same participants.