title: Longitudinal associations of age and prenatal lead exposure on cortisol secretion of 12-24 month-old infants from Mexico City.
abstract: BACKGROUND
  Cortisol 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.
  
  
  METHODS
  We 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.
  
  
  RESULTS
  Our 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).
  
  
  CONCLUSIONS
  Basal 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.
authors.affiliation: National Council of Science and Technology, Center for Nutrition Research and Health, National Institute of Public Health, 7a. Cerrada de Fray Pedro de Gante # 50, Col. Sección XVI Tlalpan, C.P. 14080, México D.F., Mexico. marcela.tamayo@insp.mx.|Center for Research in Nutrition and Health, National Institute of Public Health, Universidad No. 655, Col. Santa María Ahuacatitlán, Cerrada los Pinos y Caminera, CP. 62100, Cuernavaca, Morelos, Mexico. marcela.tamayo@insp.mx.
authors.forename: Marcela
authors.initials: M
authors.lastname: Tamayo Y Ortiz
authors.affiliation: Center for Research in Nutrition and Health, National Institute of Public Health, Universidad No. 655, Col. Santa María Ahuacatitlán, Cerrada los Pinos y Caminera, CP. 62100, Cuernavaca, Morelos, Mexico. mmtellez@insp.mx.
authors.forename: Martha María
authors.initials: MM
authors.lastname: Téllez-Rojo
authors.affiliation: Departments of Pediatrics and Preventive Medicine, Pediatrics Kravis Children's Hospital, New York, USA. rosalind.wright@mssm.edu.|The Mindich Child Health & Development Institute, Icahn School of Medicine at Mount Sinai, Annenberg Building Floor 14th Floor Room 8, 1468 Madison Avenue, New York City, NY, 10029, USA. rosalind.wright@mssm.edu.|Department of Preventive Medicine, Icahn School of Medicine at Mount Sinai, 17 East 102 Street Floor 3 West Room D3-110, New York City, NY, 10029, USA. rosalind.wright@mssm.edu.
authors.forename: Rosalind J
authors.initials: RJ
authors.lastname: Wright
authors.affiliation: Department of Biostatistics, Harvard T.H. Chan School of Public Health, 655 Huntington Avenue, Building II, Room 413, Boston, MA, 02115, USA. bcoull@hsph.harvard.edu.
authors.forename: Brent A
authors.initials: BA
authors.lastname: Coull
authors.affiliation: Departments of Pediatrics and Preventive Medicine, Pediatrics Kravis Children's Hospital, New York, USA. robert.wright@mssm.edu.|The Mindich Child Health & Development Institute, Icahn School of Medicine at Mount Sinai, Annenberg Building Floor 14th Floor Room 8, 1468 Madison Avenue, New York City, NY, 10029, USA. robert.wright@mssm.edu.|Department of Preventive Medicine, Icahn School of Medicine at Mount Sinai, 17 East 102 Street Floor 3 West Room D3-110, New York City, NY, 10029, USA. robert.wright@mssm.edu.
authors.forename: Robert O
authors.initials: RO
authors.lastname: Wright
mesh_terms: D000328:Adult; D000367:Age Factors; D000393:Air Pollutants / Q000032:analysis / Q000097:blood; D002675:Child, Preschool; D002947:Cities; D005260:Female; D006801:Humans; D006854:Hydrocortisone / Q000378:metabolism*; D007223:Infant; D007854:Lead / Q000032:analysis* / Q000097:blood; D008297:Male; D018811:Maternal Exposure; D008800:Mexico; D011247:Pregnancy; D011297:Prenatal Exposure Delayed Effects; D012463:Saliva / Q000378:metabolism*; D013977:Tibia / Q000737:chemistry; D055815:Young Adult
chemical_list: D000393:Air Pollutants; D007854:Lead; D006854:Hydrocortisone