Many people assume that the more testosterone, the better, but a new University of Michigan study finds that might not always be the case in romantic relationships.
Low testosterone levels may be a good thing for both men and women, who reported more satisfaction and commitment to their relationships when they had lower levels.
Higher testosterone is generally thought to be associated with attracting sexual partners, but might not be compatible with some kinds of long-term relationships, said Robin Edelstein, University of Michigan associate professor of psychology and the study's lead author.
"These findings suggest that once people are in a relationship, lower levels of testosterone may be beneficial - or may reflect better ongoing relationship dynamics," she said.
Previous studies have examined how testosterone levels are associated with the quality of men's relationships, but the new research is among the first to demonstrate the association among women.
The study used data from 39 heterosexual couples whose ages ranged from 18 to 31 and were in relationships from two months to seven years.
They answered questions about their satisfaction, commitment and investment.
Researchers concluded that the quality of a person's relationship was associated with own and their partner's testosterone levels.
Both men's and women's testosterone was negatively correlated with their own and their partner's satisfaction and commitment.
The couples were more satisfied and committed when they or their partner had low testosterone levels, researchers found.
The findings appear in the journal Hormones and Behaviour.