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Testosterone levels of women react in the same way as those of men: a steady relationship lowers the level, and the arrival of child lowers it even further. But as children grow up the testosterone level rises again, according to a human study done at the University of Rochester.
The concentration of testosterone in men's bodies decreases if they have a steady relationship [Horm Behav. 2003 Aug;44(2):119-22.], and even more if they take care of children. This is confirmed by a number of studies including one published in 2006 by researchers at Charles Drew University in which they measured the testosterone concentration in the saliva of 126 Chinese men aged between 21 and 38.
In the study we're covering here married men with children had 44 percent less testosterone in their saliva than unmarried men without children.
According to a study published in 2011 in PNAS [Proc Natl Acad Sci U S A. 2011 Sep 27;108(39):16194-9.], the testosterone level of men who are looking after children younger than one month goes down by about 100 picogr/ml.
When the children are over one month, their fathers' testosterone levels slowly start to rise again.
Biologists believe that caring for young children costs lots of energy and as a result testosterone levels decline. Broken nights and stress also play a role. They also suspect that evolution has programmed men to produce less testosterone during the period that they are caring for young children. Testosterone stimulates aggression and sexuality, both of which are extremely useful for ensuring the survival of the human species, but not when it comes to looking after young children.
Until recently nothing was known about what happens to women's testosterone levels throughout the course of their lives. In textbooks you can find figures like the one below, which show that the amount of testosterone in the saliva of premenopausal women fluctuates with the menstrual cycle, and suddenly declines post menopause. But apart from that not much was known.
Researchers at the University of Rochester studied 195 Norwegian women aged between 25 and 35. There was less testosterone in the blood of the women who were married, and even less in the women who were caring for a child under the age of three. [< =3]
As the age of the youngest child increased, the testosterone level of the women rose.
The researchers believe that reduced testosterone levels as a result of looking after children are temporary in women as well. The more the children can do for themselves, which requires less energy on the part of their mothers, the more the women's testosterone level starts to rise.
"Future work should address longitudinal changes in female testosterone levels over time, the biological mechanisms underlying the relationships, and the association between testosterone and quantity and quality of direct maternal care", the researchers write.
Marriage and motherhood are associated with lower testosterone concentrations in women.
Testosterone has been hypothesized to modulate the trade-off between mating and parenting effort in males. Indeed, evidence from humans and other pair-bonded species suggests that fathers and men in committed relationships have lower testosterone levels than single men and men with no children. To date, only one published study has examined testosterone in relation to motherhood, finding that mothers of young children have lower testosterone than non-mothers. Here, we examine this question in 195 reproductive-age Norwegian women. Testosterone was measured in morning serum samples taken during the early follicular phase of the menstrual cycle, and marital and maternal status were assessed by questionnaire. Mothers of young children (age ?3) had 14% lower testosterone than childless women and 19% lower testosterone than women who only had children over age 3. Among mothers, age of the youngest child strongly predicted testosterone levels. There was a trend towards lower testosterone among married women compared to unmarried women. All analyses controlled for body mass index (BMI), age, type of testosterone assay, and time of serum sample collection. This is the first study to look at testosterone concentrations in relation to marriage and motherhood in Western women, and it suggests that testosterone may differ with marital and maternal status in women, providing further corroboration of previous findings in both sexes.
PMID: 23123222 [PubMed – indexed for MEDLINE] PMCID: PMC354012
Source: http://www.ncbi.nlm.nih.gov/pubmed/23123222
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