Abstract
BackgroundCortisol has functions on homeostasis, growth, neurodevelopment, immune function and the stress response. Secretion follows a diurnal rhythm that mediates these processes. Our objective was to examine the association between prenatal lead exposure and infant diurnal cortisol rhythms.MethodsWe measured infant cortisol rhythms in saliva collected repeatedly over 2 days at either 12 (n = 255) or 18–24 (n = 150) months of age. Prenatal lead exposure was assessed by measuring maternal pregnancy blood lead levels and early postnatal maternal bone lead content. We analyzed age-specific basal secretion and the association between trimester-specific and cumulative lead exposure with a) change in total diurnal cortisol and b) the shape of the cortisol curve across the length of the day.ResultsOur results showed age related differences in salivary cortisol secretion and an age dependent association with maternal lead exposure. In age-stratified models we saw an inverse association between lead and cortisol levels in 12-month-old infants and a positive association for 18–24-month-old infants. For the 12-month-old infants 2nd-trimester-lead ≥10 μg/dL was associated with 40 % lower cortisol levels (95 % CI (−57, −16)) and a significant change in the shape of the cortisol curve (p = 0.01), compared to infants with low blood lead levels (<5 μg/dL).ConclusionsBasal cortisol secretion changes with age. Increased early gestation lead exposure alters diurnal cortisol rhythms and the association is modified by infant age, perhaps representing an early maturation of cortisol homeostasis.Electronic supplementary materialThe online version of this article (doi:10.1186/s12940-016-0124-1) contains supplementary material, which is available to authorized users.
Highlights
Cortisol has functions on homeostasis, growth, neurodevelopment, immune function and the stress response
Our main objectives were to investigate: a) if there is an age-dependent difference in the association of lead with cortisol rhythms, b) the association between lead and infant diurnal cortisol rhythms, and we hypothesized that higher prenatal lead exposure would be associated with increased cortisol production over the course of the day and c) if a specific window of prenatal susceptibility to lead could be identified
More information on cortisol concentrations by sample and for saliva collection times can be found in Table 1 of the Additional file 1
Summary
Cortisol has functions on homeostasis, growth, neurodevelopment, immune function and the stress response. Our objective was to examine the association between prenatal lead exposure and infant diurnal cortisol rhythms. Research on environmental chemical toxicants and their effects on infant or early childhood HPA axis functioning which regulates cortisol excretion [10,11,12] remains limited. Studies examining associations with exposure to other environmental chemicals in early development have suggested an increase in cortisol production and suggest that effects may vary based on developmental stage of exposure and effect measurement of HPA function [16]. The present study expands upon this prior research by examining the relationship between prenatal exposure to Pb and basal HPA axis functioning (rather than the response to a stressor), as characterized by infant diurnal cortisol rhythms measured using timed salivary samples, in 12–24 month-old infants in a Mexican birth cohort. For objectives a and c, we hypothesized that there would be a difference in the association depending on infant age and that a specific prenatal window of exposure would be detected, we preferred not to define a direction or magnitude of the effect (objective a) or to point at a specific window (objective c) due to lack of human studies on this specific theme
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