Scientists may have come one step further in decoding the essential factors for an optimal long-term relationship. It turns out that testosterone may play a central role. Specifically, high levels of the hormone may predict poor relationship quality.

Research has established that testosterone essentially has two faces. On the one hand, it is associated with sexuality and competition, and nurturance and caregiving on the other hand. While it seems to facilitate sexual unions, high levels of the hormone have also been linked to difficulties with nurturing relationships. Indeed, a slew of studies has demonstrated that men and women in committed and monogamous relationships tend to have lower testosterone levels by comparison to their single counterparts. Moreover, men who are in romantic partnerships who have lower levels of testosterone display better adjustment to long-term relationships. This includes increased marital satisfaction, decreased inclination to cheat, and decreased probability of divorce as compared to men with higher levels of testosterone.

Multiple lines of research suggest that low levels of testosterone are associated with established relationships. For example, married men typically have lower levels of testosterone than their single counterparts; similarly, men in long-term partnerships tend to have lower levels of testosterone than those in new relationships. What's more, studies suggest that nurturing environments can diminish testosterone levels. And the converse has also been found, as testosterone has been related to behaviors that undermine close relationships, including decreases in empathy and trust.

Yet to what extent does an individual's contentment with his/her relationship hinge on his/her partner's testosterone level? This question was explored in a new study led by Robin Edelstein of the University of Michigan. She and her colleagues reasoned that because of the intertwining nature of relationships, testosterone levels could influence relationship quality through, for example, levels of nurturance or conflict.

In order to investigate this question, she and her colleagues recruited heterosexual couples, with relationship length ranging from two months to seven years (three couples were engaged or married, and two were parents). The researchers were careful to exclude participants with physical conditions that might influence testosterone levels (e.g., Polycystic Ovarian Syndrome), and, similarly, women who were on the pill. Participants' testosterone levels were measured, and they completed three sub-scales of the Investment Model Scale, which assesses relationship quality. The three dimensions were satisfaction, commitment, and investment. The questionnaire included items such as: “I want our relationship to last forever”; “I feel very attached to our relationship—very strongly linked to my partner”; “My partner and I share many memories”; and “I have invested a great deal into our relationship that I would lose if the relationship were to end.” Participants then rated the degree to which they agreed with the statement.

What did the researchers find? Men and women who reported higher relationship satisfaction and commitment have lower levels of testosterone than those who report lower satisfaction and commitment. And though testosterone has previously been linked to men's relationship quality, this study appears to be the first to establish similar associations among women. Moreover, the results provide new evidence that a person's relationship quality decreases as his or her partner's testosterone levels increase, and, curiously, that such associations are stronger among men than women.

The authors note a number of limitations, including the direction of causality between testosterone and relationship quality. Yet they also assert that there is a solid basis to expect that higher testosterone levels would hamper positive relationship behaviors. For example, a recent study suggests that testosterone administration decreases “pro-social emotions” such as trust, empathy, and generosity, which could compromise relationship quality. At the same time, it may be that relationship quality effects testosterone levels. For instance, the authors reference longitudinal and experimental research demonstrating that warm and fuzzy interactions with babies diminishes men's testosterone. Ultimately, though, the investigators say the testosterone-relationship quality associations are probably reciprocal, with each influencing the other to some degree over time.

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