Plasma oxytocin distributions in a large cohort of women and men and their gender-specific associations with anxiety

Research has consistently addressed the relations between plasma oxytocin (OT) - a nonapeptide implicated in mammalian social bonding - and psychological distress, but the direction of the association remains unclear. Utilizing the largest sample of plasma OT to date (N = 473), the current study had two goals. First, we described the distributions of plasma OT in women and men, and second, we examined whether the relations between OT and two types of anxiety - trait and attachment anxiety - are moderated by gender. Results indicated that OT values (M = 375.78 pg/ml, SD = 264.03, range = 51.40-2752.30) clustered around the mean with a long right tail, indicating trend toward high values. In most participants (N = 323), OT was measured again six months after initial assessment and OT levels were highly stable within individuals. After removing outliers 2.5 SD above the mean (≥1098 pg/ml for men and ≥988 pg/ml for women), men showed significantly higher mean OT than women (women: 327.13 pg/ml, SD = 164.43; men: 399.91, SD = 183.65; t = 2.57, p = .01). Gender was found to moderate the relations between OT and anxiety. Trait anxiety was lower among men with higher OT but no such links emerged for women, supporting the hypothesized anxiolytic effects of OT in males only. Furthermore, women with extreme values (≥988 pg/ml) had three times the probability of being classified as highly anxious (STAI-T ≥ 45). Higher OT in women correlated with greater attachment anxiety, but no such relationships were found for men. Results are consistent with models on the differential associations between the neurobiology of attachment and the experience of anxiety in women and men.