The Effect of Relationship Status on Testosterone Levels in Men

Researchers have long known that single men tend to have more testosterone than comparable men in long-term relationships, but what about men in new relationships?

A new study finds that testosterone generally remains at “single-man” levels until couples have been dating for more than a year.

“The similarity in levels of testosterone between men in new relationships and single men suggests that men in new relationships are still in a physiological state that aids competition with other men for access to potential mates,” the study authors wrote in Evolutionary Psychology.

“This may be due to the need to maintain and develop their new relationship… However, an alternative explanation for these effects may be due to the direction of causality. In other words, it may be that men with higher baseline levels of testosterone are more likely to terminate their relationships before they become long-term due to their greater propensity to seek new partners.”

The research team recruited 75 heterosexual young men (average age, 22.11 years), took saliva samples to test their testosterone levels and then used questionnaires to gather information about their relationships and their attitudes about sexual behavior.

Analysis showed that paired men had significantly lower levels of salivary testosterone overall than single men (mean, 86.03 pg/dl ± standard deviation, 18.87 pg/ml vs. 110.77 pg/ml ± 39.73pg/ml; p = .017) and men in new relationships (111.23pg/ml ± 37.13 pg/ml; p = .037).

However, there was no difference in overall testosterone levels between men in new relationships and single men (p = .96).

The researchers recalculated the numbers after eliminating potential confounders such as men with children and men whose socio-sexual orientation inventory (SOI) scores indicated a willingness to cheat that belied the concept of a monogamous relationship. None of these changes produced any significant change in findings.

The researchers also checked to see whether any other factors were associated with significantly higher or lower levels of testosterone — factors such as age, relationship quality or SOI scores — and they found only 1.

Among men in long-term relationships, higher levels of salivary testosterone were associated with higher scores on the SOI-attitude scale, which measures how theoretically open people are to sexual experience, and the SOI-behaviors scale, which measures how much sex they actually have.

The study team acknowledged several potential limitations in its work, limitations such as the relatively small cohort and the relative homogeneity of that cohort.

A more important limitation may have been the somewhat arbitrary decision to make a single sharp split between “new” relationships and “long-term” relationships at the 12-month mark. That said, they believe the strength of their findings indicates that the 1-year mark is pretty close to the threshold point in the minds of many men.

“The research in this area has broadened the conditions under which it is predicted that levels of testosterone in men will vary (ie, going beyond classifications based simply on marriage and fatherhood to more precise classifications involving socio-sexual orientation and interest in extra-pair sexual activity),” the study authors wrote.

“However, the underlying evolutionary explanation (changes in testosterone in response to changes in motivation to compete with other men) has remained constant and shows an increased sophistication of our understanding on how this may relate to modern human behavior.”