Postnatal Testosterone Levels and Temperament in Early Infancy

Recent research showing associations between behavior and postnatal testosterone levels in male infants has suggested that the transient activation of the hypothalamic-pituitary-gonadal axis in early infancy may influence the expression of gender phenotypes in later development (i.e., the postnatal hormone hypothesis). As a further test of the relationship between postnatal hormones and behavior in infancy, we measured digit ratios and salivary testosterone in 76 male and female infants (3–4 months of age) and parents completed the Infant Behavior Questionnaire-Revised, a well-established measure of temperament in the first year of life. Consistent with our earlier findings, there were no significant sex differences in salivary testosterone levels and testosterone levels were unrelated to measures of behavior in female infants. However, in male infants, higher androgen levels predicted greater Negative Affectivity. Further examination of the four scales contributing to the measure of Negative Affectivity showed testosterone levels were a significant predictor of scores on the Distress to Limitations scale, but not of scores on Fear, Sadness, or Reactivity scales. This sex-specific association between salivary testosterone and behavior in infants is consistent with animal research showing higher prenatal androgens associated with typical male development lower the threshold of sensitivity to endogenous testosterone in postnatal life. In sum, these data provide additional support for the postnatal hormone hypothesis and suggest postnatal testosterone levels may influence the development of emotional regulation in male infants.     

The Association of Formula Protein Content and Growth in Early Infancy: A Systematic Review and Meta-Analysis

This systematic review aimed to examine differences in growth outcomes between breastfed infants and infants fed with formula with different protein/energy ratios during the first six months of life. We conducted a systematic review in the PubMed, Web of Science, and Springer databases. Twenty clinical trials qualified for inclusion. We extracted data about the growth outcomes of infants who were exclusive breastfed or exclusively infant formula fed in the first six months and used a meta-analysis to pool the finding data. We categorized study formulas into four groups according to their protein content: <1.8, 1.8–2.0, 2.1–2.2, and >2.2 g/100 kcal. In the first month of life, growth was not different between formula- and breastfed infants. During 2–3 months of life, growth was faster in infants who consumed formulas with protein contents higher than 2.0 g/100 kcal. After 3 months, formula-fed infants grew faster than breastfed infants. Our meta-analysis indicated that the growth outcomes of infants fed with infant formula with a relatively low protein/energy ratios, compared with that a relatively high protein/energy ratio, were close to those of breastfed infants.     

Severe Lower Respiratory Tract Infection in Early Infancy and Pneumonia Hospitalizations among Children,Kenya

Severe lower respiratory tract infection (LRTI) in infants caused by respiratory syncytial virus (RSV) has been associated with later pneumonia hospitalization among children. To determine risk for pneumonia after RSV hospitalization in infancy, we conducted a retrospective cohort analysis of 2,813 infants admitted to a hospital in Kenya and identified readmissions for pneumonia among this group during early childhood (<60 months of age). Incidence of readmission for pneumonia was higher for children whose first admission as infants was for LRTI and who were <3 months of age than for children who were first admitted as infants for non-LRTI, irrespective of RSV status. Incidence of readmission for pneumonia with wheeze was higher for children whose first admission involved RSV compared with those who had non-RSV LRTI. Excess pneumonia risk persisted for 2 years after the initial hospitalization. Close postdischarge follow-up of infants with LRTI, with or without RSV, could help prevent severe pneumonia later in childhood.