Why boys talk later than girls: hormones?

Studies have shown that language development varies between the sexes, with males generally gaining language skills at a slower rate. Prenatal testosterone is known to influence fetal neurodevelopment, and preliminary studies have suggested that the hormone is associated with language delay.  Researchers from the U of Western Australia explored this issue in a large cohort of children.  They collected umbilical cord blood samples from 861 randomly selected births and measures the bioavailable testosterone levels.  As expected the males had a much higher level of testosterone in the umbilical cord blood than the females. For the following three years the parents completed an Infant Monitoring Questionnaire annually that measured communication (language), gross-motor, fine-motor, adaptive and social development.

As previously reported in other studies, a greater proportion of males had greater communication delay at all three assessments stages.  In addition to the language deficits, males were more likely to have delays in fine-motor function and personal-social skills at age 3.  Conversely, females exposed to the highest levels of testosterone had a reduced likelihood of having a language delay at that age.

This study suggests that high prenatal testosterone levels are a risk factor for language delay in male children.  In contrast to the increased risk for delay in males, higher levels of testosterone appeared to reduce the risk of language delay among females.

Males exposed to the highest testosterone levels were more than twice as likely to have a language delay at age 3, according to Andrew Whitehouse, PhD, of the University of Western Australia in Perth, and colleagues.

“These data suggest that high prenatal testosterone levels are a risk factor for language delay in males, but may be a protective factor for females,” according to Whitehouse.   “Replication of these findings is essential, and may help refine our understanding of the level of testosterone that is associated with a detrimental effect on language development in boys.”  The researchers expected the results in males but found it difficult to explain the protective effect in females.

They speculated that it might have to do with sex differences in how the brain lateralizes function across left and right hemispheres.
Source reference:
Whitehouse A, et al “Sex-specific associations between umbilical cord blood testosterone levels and language delay in early childhood” J Child Psychol Psychiatry 2012; DOI: 10.1111/j.1469-7610.2011.02523.x.