Hair Cortisol and Hair Testosterone Concentrations in Internet Addiction

Abstract Internet addiction (IA) has been consistently shown to be closely associated with stress; however, studies on physiological stress in IA have yielded mixed findings regarding the relationship between IA and cortisol. In addition, the role of testosterone—another hormone potentially relevant to addiction—has been scarcely examined in IA. The present study investigated associations between IA and long-term basal secretion of cortisol and testosterone using hair-based hormone measures. A total of 155 Japanese undergraduate and graduate students (94 females, mean age = 21.1 years, standard deviation = 4.1 years) participated in the study. IA severity was assessed using the Japanese version of the Internet Addiction Test (Osada, 2013; Young, 1998). Hair cortisol and hair testosterone concentrations, reflecting cumulative hormone secretion over the preceding three months, were quantified using enzyme-linked immunosorbent assays. A multivariate regression analysis revealed a significant interaction between hair testosterone and sex; higher hair testosterone concentrations were positively associated with IA severity in females but not in males. These results suggest that IA may be linked to altered long-term activity of the hypothalamic–pituitary–gonadal axis in females. By jointly examining cortisol and testosterone, the present findings extend previous research that has largely focused on single hormonal systems.