Link between mental health and self-reported number of digital hairs suggests new way to measure expressed testosterone
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There is growing consensus that testosterone is related to mental and physical health, but the underlying mechanisms are still poorly understood. One explanation for the conflicting results found in the study of testosterone is that this hormone is needed for the arousal that signals the expectation of a positive outcome, meaning that high testosterone can be expected to lead to impulsive behavior and thus enhance a person’s risk to develop an anxiety disorder, whereas low testosterone would lead for instance to apathy and thus enhance a person’s risk to develop a mood disorder. To investigate this hypothesis I explored the relation between emotionality, mental health and the self-reported number of digital hairs as an indicator of expressed testosterone in an online survey in which 316 Dutch (speaking) men and women participated. Using factor analysis on a pool of items probing the participant’s tendency to react emotionally I identified four types of emotionality: an internalized negative type, a positive type, a sexual type and an externalized negative type. I found that mental health was indeed higher at intermediate levels of digital hair, and that there was a positive association between general emotionality and digital hair, though only in partnered persons and women. These results should be interpreted with caution because data were collected during the COVID-19 pandemic and with the exception of partnered men all participants had relatively low scores on the used measure for mental health. Nevertheless, the fact that by using the digital hair measure a distinct pattern was found suggests that this measure may be employed as an easy to use and non-invasive marker for expressed testosterone, although the measure is probably more reliable if the assessment is done by a trained assessor, especially in men as they have more digital hair then women. To further elucidate the association between testosterone and reward related arousal I introduce the concept of reiteration as the phenomenon that links perception, representation and behavior.