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Your Environment. Your Health.

Lower Leukemia Risk Associated with Day Care Attendance or Prolonged Breastfeeding

Catherine Metayer, Ph.D.
University of California, Berkeley
NIEHS Grants P01ES018172, R01ES009137, R13ES021145, R13ES024632, P42ES004705

Findings from a large pooled analysis reinforce the hypothesis that day-care center attendance in infancy and breastfeeding for at least six months are associated with a decreased risk of acute lymphoblastic leukemia (ALL). ALL accounts for 80 percent of childhood acute leukemia, which is the most common cancer for children under 15 years old.

The researchers used data from 11 case-control studies participating in the Childhood Leukemia International Consortium to examine the association between ALL and early stimulation of the immune system. To do this, they looked at day care attendance, birth order, breastfeeding, and maternally reported common infections in infancy. The study included 7,399 ALL cases and 11,181 controls who were 2 to 14 years old.

The researchers found that attending day care during the first year of life was associated with a reduced risk of ALL (odds ratio = 0.77, 95 percent confidence interval: 0.71, 0.84). The earlier a child began day care, the lower the risk of ALL (P < 0.0001). The researchers also observed a reduced risk associated with breastfeeding for 6 months or more (odds ratio = 0.86, 95 percent confidence interval: 0.79, 0.94).

Although early exposure to common infections may be responsible for the association with day care, there was no significant relationship between ALL and common infections in infancy. Thus, understanding the potential mechanisms involved in this association requires assessing both the severity and the timing of infections, according to the researchers.

Citation: Rudant J, Lightfoot T, Urayama KY, Petridou E, Dockerty JD, Magnani C, Milne E, Spector LG, Ashton LJ, Dessypris N, Kang AY, Miller M, Rondelli R, Simpson J, Stiakaki E, Orsi L, Roman E, Metayer C, Infante-Rivard C, Clavel J. 2015. Childhood acute lymphoblastic leukemia and indicators of early immune stimulation: a Childhood Leukemia International Consortium study. Am J Epidemiol 181(8):549-562.