September 12, 2011

expert reaction to the biological effects of day care as published in The Biologist, a journal of the Society of Biology

An article by psychologist Aric Sigman claimed to link day care with various biological effects in children.

Prof Dorothy Bishop, Professor of Developmental Neuropsychology, University of Oxford, said:

“Sigman is undoubtedly passionate in his zeal to protect children from negative effects of daycare, but this account seems unbalanced as it presents only the evidence for negative effects of stress on neural function. A more common view of those who do research in this area is that chronic unremitting stress is undoubtedly bad for development, but the impact of mild intermittent stress is much harder to evaluate, and can be beneficial in promoting resilience. As far as daycare is concerned, there is broad consensus that it influences the cortisol levels of young children in the short term, but there is no evidence that this has long-term detrimental consequences, especially if the quality of childcare is high. Sigman argues that people don’t talk about long-term negative effects of daycare because it is politically unacceptable, but there’s a simpler explanation: they don’t talk about these effects because they haven’t been demonstrated, and such research as there is indicates a highly complex relationship between stress responses, hormones, neurodevelopment and behavioural outcomes.”

Dr Andrea Danese, Clinical Lecturer in Child & Adolescent Psychiatry, King’s College London, said:

“Investigation into the mechanisms through which early experiences influence child development and adult health is an active and exciting area of research. In this article, the author maintains that stress owing to day-care attendance, or the associated increase in stress hormone cortisol, is harmful to children and has enduring consequences on health. This is a simplistic and misleading way to portray the relevant research findings to date.

“There are several ways in which challenging early experiences can affect child development. For example, research shows that exposure to stimulation and mild stressors in young children can promote the development of effective coping strategies in the face of challenging circumstances in later life. This phenomenon, known as stress inoculation, resembles the practice of vaccination, where children are inoculated with mild forms of pathogens in order to strengthen their immune response in later life. In addition to this ‘positive’ stress, ‘toxic’ stress can also occur. Maltreated children exposed to overwhelming and prolonged forms of abuse and violence have enduring elevation in cortisol levels, as well as changes in brain and immune system functioning. These extreme forms of early life stress have also been associated with increased risk of mental and physical disease in later life.

“To date, there is no evidence to suggest that children attending day-care suffer similar detrimental consequences. The one study that measured cortisol levels repeatedly over time showed that children attending day-care have only transient elevation in this stress hormone, a normal physiological response to new, unpredictable circumstances. Furthermore, there is no research study that has found a clear and direct link between day-care attendance and disease in later life.”

Dr Stuart Derbyshire, Reader in Psychology at the University of Birmingham, said:

“Parents should treat Dr. Aric Sigman’s report with extreme scepticism. The hormone increases that Sigman associates with day-care are not surprising; children who attend day-care are bound to have some physiological differences from children who stay at home because they do different things. Maybe kids in day-care run around more and that increases their hormone levels. Sigman’s extreme conclusions, that children attending day care are at risk from heart disease, dementia, eczema, general increased illness frequency and psychological dysfunction, are unwarranted and unsupported. On all these issues the scientific evidence is inconsistent, uncertain, indirect and weak, which is understandable because day-care, and life, is complicated. Reducing day-care to a singularly negative influence is advocacy not science. Is there an upside to attending day-care? Or a downside to staying at home? On these issues, Sigman is tellingly silent.”

Additional information from Prof Dorothy Bishop: “In this article, Dr Sigman ambitiously attempts to link diverse areas of research: the effects of childcare on stress responses in children (as indexed by salivary cortisol) and the effects of cortisol on brain structure and function. There is good evidence from a number of studies now that children attending childcare have enhanced cortisol responses compared to those who stay at home. This effect can be seen within children, i.e. the cortisol responses differ depending on whether the child is at home or in daycare. Sigman cautions that this could have an important and long-lasting effect on brain development, on the basis of reviewing a range of studies of cortisol effects in the elderly, people with psychiatric disorders, and rodents. The problem is that the link between the different domains of study is still speculative, especially in view of studies that report beneficial effects of mild levels of stress. “For instance, one of the papers that Sigman reviewed described a study on monkeys thus: ‘As in the work on cortisol responses to fullday child care, these separations in squirrel monkey infants produced marked and repeated activations of the HPA axis. However, followed into the late juvenile and early adult age, animals exposed to this form of early life stress were found to be less fearful, to produce lower rather than higher cortisol responses to stressors, and to show more optimal development of prefrontal regulatory brain circuits; consistent with these findings, they also performed better on tests of executive functioning. Thus, at least for this animal model, repeated separation stress early in life fostered a form of resilience.’ Gunnar et al (2010) (my emphasis). “In a similar vein, a major review of neurobiology of stress by McEwen (2007) is also cited by Sigman, but he ignores an entire section entitled ‘Protection and Damage: The Two Sides of the Response to Stressors’, in which McEwen notes that there are situations where stressors are beneficial to brain function. Cortisol, which Sigman regards as ‘neurotoxic’ can enhance learning in some situations.”
Mother Superior?: the biological effects of day care by Aric Sigman, published in The Biologist on Monday 12 September 2011.