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Toddlers, particularly shy ones, release more stress hormone at child care centers than they do at home, which raises the question of whether group day care could affect brain development in timid kids, a study reports today.
Shy children had the biggest increases in cortisol, a stress hormone, during their time at day care. Large doses of cortisol shorten the life of brain cells in animals. But there's no solid research on how the modest increases seen in kids at day care might affect their developing brains, says University of Minnesota psychologist Megan Gunnar, the study's leader.
Gunnar and co-author Sarah Watamura studied 67 infants and toddlers attending child care centers full time. Their report is in the journal Child Development.
About seven of 10 toddlers, ages 16 months to 38 months, increased their output of cortisol at child care. On days at home, most didn't have increases in the stress hormone. Infants had similar cortisol output at day care and home, but the older babies began to have rising stress hormones at day care, Gunnar says. Toddlers who played less with other kids and those rated as ''socially fearful'' by teachers tended to put out the most cortisol.
Cortisol is a ''fight or flight'' hormone that helps people cope with challenging events, and group day care could be a challenge for timid kids, Gunnar says. ''Teachers tend to pay a lot of attention to those who are causing trouble and less attention to the dog that isn't barking, the quieter ones at the fringes.''
Older toddlers show smaller increases than the younger ones, ''and that's reassuring,'' Gunnar says, because it suggests kids adapt. Also, there's strong evidence that high-quality day care promotes cognitive development. Other studies find that increases in stress hormones correlate with poor-quality day care, but this study did not consider quality, she says.
Cortisol surges in adults can hinder the immune system, and that might help explain why toddlers in group care are prone to getting colds and viruses, she adds.
One small study on family day care found smaller cortisol rises than at centers. There's no research on nanny care yet, Gunnar says.
The best day care centers can meet the needs of even timid children, ''and we don't know that keeping them home longer with a nanny helps them,'' says Stanford University psychologist Eleanor Maccoby, an expert on child development.
Still, shy kids might benefit from some home care ''if finances allow it,'' she says. ''We know the environment can program the nervous system, and there might be a little risk to putting a very fearful toddler in some child care centers.''
The study isn't detailed enough to tell how group care affects health, says psychologist Karen Matthews of the University of Pittsburgh. ''It does suggest there's a group of sensitive kids who find center care overwhelming. We don't know how this care will affect them in the long run.''
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