The Durk Pearson & Sandy Shaw®
Life Extension NewsTM
Volume 13 No. 3 • June 2010


Psychobiochemistry
Testosterone Decreases Trust in
Human Social Relationships

A very interesting new paper1 appeared this month in the Proceedings of the National Academy of Sciences on the subject of the effect of testosterone on human trust. While the hormone oxytocin has been associated with bonding and increased trust in humans, including both men3 and women, as well as other mammals, testosterone is now identified as increasing social vigilance and decreasing interpersonal trust in humans. The researchers suggest that testosterone “may have antagonistic properties with oxytocin.”

The authors used a facial trustworthiness test to assess how much trust different individuals attached to different nonfamiliar human faces. This test is said to be “highly validated” when unconfounded by rewards and that “these judgments are also highly correlated with investments in an economic-trust task.”1

Twenty-four healthy young women were the subjects (mean age 20.2) in this study. The authors explain that they did not include men because the kinetic parameters (quantity and time course) for inducing neurophysiological effects after a single sublingual administration of 0.5 mg (500 mcg) of testosterone have been established in women, but are unknown in men. The testosterone was administered sublingually because, if swallowed it would be destroyed in the first pass through the liver.

As the researchers point out, trust is an important factor in human society (human relationships, including commerce, could not exist without a certain degree of trust), but that too much trust could lead to costly interactions with individuals who are not trustworthy. “Thus, those who are willing to believe what others say, or fail to probe the motivations underlying their actions, may fall prey to considerable economic and social costs.”1 Because humans are not only social but also compete for resources, there has to be a balance between trust and vigilance. Or, as the authors memorably put it, testosterone is a “steroid hormone with potentially toxic consequences for human sociality [that] might counteract the maladaptive aspects of trust.”

A recent study,2 as cited by the authors of paper #1, showed “higher trustworthiness ratings to unfamiliar others after oxytocin administration compared with placebo, demonstrating the validity of using a comparable paradigm for measuring trustworthiness.”1

The results of the study1 showed a significant overall reduction in trustworthiness ratings after testosterone as compared with placebo. “The hormone acted selectively on our high-trusting subjects, defensibly to down-regulate their trust to a level more advantageous in the competition for resources.”1 However, as the authors explain, the down-regulation of trust after testosterone administration in the present study “was restricted to high-trusting, thus most socially naive half of our subject group, and may for that reason be adaptive in the competition for status and resources.” “A socially vigilant stance is vital for gaining and maintaining dominance or leadership ...”

References

  1. Bos et al. Testosterone decreases trust in socially naive human. Proc Natl Acad Sci USA 107(22):9991-5 (June 1, 2010).
  2. Theodoridou et al. Oxytocin and social perception: oxytocin increases perceived facial trustworthiness and attractiveness. Horm Behav 56(1):128-132 (2009).
  3. Kosfeld et al. Oxytocin increases trust in humans. Nature 435(7042):673-6 (2005).

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