MOTHER SUPERIOR? The biological effects of day care - Sichere Bindung
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B ENDOCRINOLOGY
THE BIOLOGICAL EFFECTS OF DAY CARE
MOTHER SUPERIOR?
The biological effects of day care
The relative effects of stay-at-home mothering and institutional day care on the mental
and physical development of toddlers have long been debated by psychologists.
Here Dr Aric Sigman takes a novel and neuroendocrinological perspective
28 THE BIOLOGIST Vol 58 No 3
T
he accepted starting point for BIOGRAPHY others have suddenly found their Until now, such information has
any national discussion of research data re-analysed prior to remained in specialised journals and
childcare is one of a “work- publication (Belsky 2001; Henry has not been widely reported by the
childcare balance” involving 2006; James 2010). However, the national media. By bringing together
“affordable day care”. Even many of uncomfortable question remains – this under-exposed area of research
those forging academic careers in which is better for a young child to form a solid body of evidence, it is
the study of day care are apparently during weekdays: the biological possible that society will be able to
being held back by their own young mother or a paid carer at an make more fully informed decisions
children. “Tiny tots can prove Dr Aric Sigman institution? about the future direction of
formidable foes to a woman’s CBiol FSB is a Until now, research on the effects childcare.
academic career aspirations… The Fellow of the Royal of day care has been dominated by
shortage of high-quality, affordable Society of child psychology and social work, The HPAA axis
Medicine and
day care is enough to make academic focusing on later outcomes for the The hypothalamic–pituitary–
Associate Fellow
parents cry,” states a Special Report of the British child such as language skills at age adrenal axis (HPAA) is a system
in Nature (Gewin 2005). Psychological five or six. But what has proved intricately involved in a child’s
Half of British mothers go out to Society. He has elusive is an understanding of how capacity to respond to fear or
work before their child is 12 months travelled to the young child is affected uncertainty. Neuroendocrine
old (OECD 2011). As a result a vast various cultures, emotionally and biologically, and research of stress uses salivary
including Republic
and growing proportion of children of Congo, North
how they experience day care while samples to measure cortisol, the
under three now attend day nurseries Korea, Bhutan, they are actually there. Babies can’t steroid end product of the HPAA.
and both the UK and the US have Tonga, West speak and toddlers have limited Cortisol levels undergo a diurnal
nationalised day care programmes Papua, Burma, verbal abilities when it comes to cycle; they peak in the early morning
(Sure Start and Head Start). Iran, Korea, describing their inner world. and decline throughout the day.
A recent report by the EU Vietnam, Borneo, However, research methods from the Infants are born without a diurnal
Mali, Bolivia,
Commission stated that in order to Burkina Faso, biosciences are starting to provide an cortisol rhythm. They acquire it
solve Europe’s labour problems, Sumatra, illuminating glimpse of this during their first year of life, and it is
many more mothers should return to Cambodia and unspoken landscape, with the child’s subject to programming. Rising
work early. Commission President Eastern Siberia to neuroendocrine responses helping to cortisol levels are healthy and
José Manuel Barroso said we “should study families and shed light on their experience. And necessary as an appropriate stress
child development.
look at the example of the northern those responses paint a very different response. However, when stress is
countries” and create more childcare picture to that presented by the day chronic, high levels of cortisol remain
places for mothers of young children care research establishment: there is active in the system and this has
(EU 2011). A new OECD report something about attending day care significant biological consequences.
Doing Better for Families, for an extended time, whether small- For example, increased cortisol
representing the policy strategy of 34 scale and home-based or large-scale exposure is linked to higher numbers
industrialised countries, concluded: and centre-based, that often triggers of plaques in artherosclerosis of
“It is crucial to mobilise maternal stress in young children. the carotid arteries (Dekker et al.
labour supply more effectively”, The University of Minnesota 2008). High cortisol levels strongly
adding that “from a career College of Education and Human predict cardiovascular death
perspective alone, women are
One report Development reports that in many (Vogelzangs et al. 2010). Cortisol is
probably best advised to go back to
suggests cases, 70 to 80 percent of children in considered neurotoxic and has a
work at an early stage after 70 to 80% centre-based day care show ever- global impact on cerebral size (e.g.
childbirth” (OECD 2011). of children increasing levels of the stress McEwen 2007; Sheline 2003) and
But day care is an evolutionary in centre- hormone cortisol throughout the exposure to elevated cortisol levels
novelty bearing no resemblance to based day day, with the biggest increases can lead to structural alterations in
childcare throughout history or in care show occurring in toddlers. Yet by age five, the brain’s amygdala (Sharpley and
modern traditional societies (Konner ever- children don’t exhibit these stress Bitsika 2010).
2005). Understanding the effects day increasing reactions to being with other Even subtle dysregulations of the
care has on children has been children all day (Gunnar 2010; HPAA, such as elevated cortisol
hindered by bitter politicised
levels of Vermeer and van IJzendoorn 2006). levels, have now been implicated
arguments involving women’s rights,
the stress Of central concern is that the routine in the pathophysiology of stress-
governmental desire for economic hormone stress experienced at day care could related disorders, including
growth, maternal guilt and the cortisol cause permanent changes in the depression and anxiety (Ostiguy et
media’s portrayal of day care study throughout child’s neuroendocrine networks, al. 2011). Cortisol levels at age
findings. Some researchers who have the day with long-term consequences 17 have recently been used to predict
voiced concerns about the effects of for their mental and physical the development of psychiatric
day care have been attacked, while health as adults. disorders during the following
Vol 58 No 3 THE BIOLOGIST 29
B ENDOCRINOLOGY
THE BIOLOGICAL EFFECTS OF DAY CARE
2.5 years (Ellenbogen et al. 2011), (2007) reported that, among three- to styles. Coloured areas denote lower
and a higher cortisol awakening eight-year-olds, those who slept in the grey matter concentrations in the left
curve may be a biological marker for In human parental bedroom had lower cortisol hippocampus found in people with
an underlying disposition towards grey matter, levels, as did children who attended high attachment anxiety scores (left).
developing depressive and anxiety the quality fewer hours of day care during the Lower grey matter concentration in
disorders (Vreeburg et al. 2010). of a mother’s first four years of life. the left as well as in the right
HPAA dysregulation may also offer a care in early A person’s approach to close hippocampus were found in people
biological explanation as to childhood relationships, or their attachment with higher attachment avoidance
why children with a relatively low is thought style, is believed to be influenced by scores (right) (Quirin et al. 2010).
socioeconomic environment (SES) to alter the early interactions with primary In children with a history of
are more likely to develop psychiatric size of the carers, particularly biological maltreatment, raised cortisol
and physical illnesses later in life. hippocampus mothers. Attachment style has now levels predict a later reduction
Chen et al. (2010) found that over a been linked with waking cortisol in the size of the hippocampus.
two-year period, cortisol levels levels in female children between the Neurodevelopmental experiences
increased almost twice as much in ages of nine and 18. Those with a more of elevated stress and cortisol are
low SES children compared with “anxious attachment style” had increasingly seen as a potential cause
those with a higher SES. higher levels on awakening and an of reductions in the size of specific
Rearing environment and cortisol attenuated cortisol awakening brain regions via a cortisol-induced
There is a close relationship between response, the same pattern linked neurotoxic brain cell reduction
maternal nurturing and cortisol levels with disorders in adulthood (Oskis process (Carrion et al. 2007). In early
in infants. A study at Sweden’s et al. 2011). childhood, activity of the HPA axis
Karolinska Institute found a strong Children who receive less nurturing resulting in cortisol secretion may
correlation between stay-at-home early in life may be less securely strain the stress response system,
mothers and child cortisol levels attached as adolescents and adults, which can in turn have a direct effect
(Stenius et al. 2008). Comparisons of with a greater vulnerability to stress. on its future ability to function
different child-rearing environments Cortisol may play a key role in the optimally when exposed to additional
show low cortisol levels in infants with finding that adolescents’ attachment stress (McEwen 2000a, b).
families who live an “anthroposophic orientation influences their diastolic
lifestyle” – thought to provide and systolic blood pressure responses Epigenetic windows
environmental conditions aimed at to everyday social interactions of sensitivity
Fig. 1. Insecure
reducing stress, compared with Attachment and (Gallo & Mathews 2006). The mechanisms by which a child’s
infants in more conventional families hippocampal cell early care experiences are translated
(Stenius et al. 2010). Waynforth density. Early years HPAA programming into physiological and behavioural
and grey matter changes are now thought to involve
In the past decade, research has epigenetic programming of the
revealed a profound influence of early- HPAA. Mothering plays a central
life childcare and parenting on the role: maternal care can produce semi-
programming of the HPAA and its permanent changes in gene
regulation in adulthood, including the expression in brain regions vital in
development of the hippocampus and stress response, thereby providing a
alterations in the cortisol awakening potential mechanism for early
response (Engert et al. 2010). In rats, childhood programming of stress-
the quality of the mother’s care induced disease in adults (Craft and
induces changes in the brain’s DeVries 2009). In rats, the degree of
structural neuroplasticity and alters maternal care alters the offspring
synaptic functioning and the response epigenome at a glucocorticoid
to anti-inflammatory hormones receptor in cells of the hippocampus,
(including cortisol) and stress. as well as altering the HPAA response
In controlled experiments, shorter to stress (Weaver et al. 2004; Weaver
dendritic branch length and lower 2009). Stress occurring during
spine density in CA1 pyramidal brain sensitive periods of development
cells are found in the hippocampi of might therefore cause lasting changes
adult offspring with mothers who in the settings and function of the
were less attentive (Champagne et al. child’s HPAA. (Murgatroyd et al.
2008). In human grey matter, the 2009; Mesquita et al. 2009; see
quality of a mother’s care in early Figure 2).
childhood is thought to alter the size Elevated levels of stress in young
of the hippocampus (Buss et al. 2007). children are of particular concern
Attachment insecurity has now been because a range of developing
significantly linked to reduced brain systems could be adversely affected.
size and cell density within the Concern is not restricted to high
hippocampus (Quirin et al. 2010; see cortisol levels; it includes any
Figure 1). dysregulation of the diurnal cortisol
Clusters of grey matter cycle or the HPAA more generally.
concentration in the hippocampus Therefore, a key element in the care
correlated with human attachment of young children is the availability of
30 THE BIOLOGIST Vol 58 No 3Windows of Epigenetic Sensitivity three to five-year-old children
“attending very high quality, full time
Neonatal childcare centres”. Salivary
Prenatal Adult antibodies provide a critical line of
defence against pathogens. Samples
were taken throughout the day, both
Stress at home and in childcare, to examine
Periods of
sensitivity the relationship between salivary
cortisol concentration and antibody
HPA axis dysregulation secretion – secretory IgA (SIgA) – and
their relationship to childhood
illnesses. The researchers found that
Physical,
Epigenetic changes, psychological “a rising cortisol profile at childcare,
mechanisms dysfunction driven by higher afternoon levels,
predicted lower antibody levels on the
subsequent weekend”.
adults, particularly parents, to Fig. 2. Epigenetic on possible associations between Of particular note was a decline
respond appropriately to stress programming of cortisol levels and quality of care, in antibody production at weekends
reactions triggered by normal HPAA. Stress and the influences of and on childcare days in older
during sensitive
day-to-day events. age, gender and children’s preschool children. They concluded
periods of child
development may temperament. Age appeared to be that “elevated cortisol in children
Day care and HPAA function cause lasting the most significant moderator of during childcare may be related to
Attending a childcare centre, and the changes in the this relation. The effect of day care both lowered antibody levels and
consequent separation from parents, settings and the attendance on cortisol excretion greater illness frequency.”
is a significant source of stress for function of the was especially notable in children (Watamura et al. 2010).
HPAA, leading to
many young children. physical and
younger than thirty-six months. Stress may activate MHC class II+,
A review and meta-analysis of psychological We speculate that children in langerin+, and CD11c+ immune cells
nine studies, Children’s Elevated disorders later centre day care show elevated in a child’s skin, which can cause
Cortisol Levels at Day Care, in life. cortisol levels because of their inflammatory skin diseases including
concluded: stressful interactions in a group eczema (Joachim et al. 2008). Using
“Our main finding was that at day setting” (Vermeer and van the German birth cohort study,
care, children display higher IJzendoorn 2006). Cramer et al. (2011) found that, of 11
cortisol levels compared to the possible risk factors for eczema
home setting. Diurnal patterns Sumner et al. (2010) compared during the first two years of life, even
revealed significant increases from children aged between 16 and 24 years later only “day care centre
morning to afternoon, but at day months on two childcare days versus attendance is associated with an
care only… We examined all papers two non–childcare days, finding that increased prevalence and incidence
“childcare days were characterized of eczema.”
by an afternoon increase in cortisol Others have found that between
levels (unlike non–childcare days)”. ages 2 to 3 the cortisol differences
Cortisol elevation at Daycare v Home Other studies have compared between home and daycare are
professional home-based and centre- transient and diminish over a year. At
19 based childcare. In one, children from 3 years of age, children displayed
18
professional childcare homes and higher cortisol levels at daycare only
children from childcare centres in the if they had a ‘later entry’, defined as
17 20 – 40 months age range were starting after 16 months, while
monitored. The study concluded: children with more daycare
e
Salivary Cortisol (μ/dl )
ar
16 “Children displayed higher cortisol experience, entering before 8
yc
Da
15
levels at childcare than at home, months, showed higher levels at
irrespective of type of care.” home. (Ouellet-Morin et al., 2010)
14 (Groenveld et al. 2010). However, the one year between ages 2
Other studies have assessed the and 3 constitutes one third of a child’s
13 effects of full-time professional home- life during the greatest period of
e
Hom based day care on HPAA function. brain development. And so even if
12
Gunnar et al. (2010) examined 151 cortisol rises diminish within a year,
11 children (3.0-4.5 years) in full-time there has been some systematic
home-based day care. “Compared to dysregulation and subtle lasting
10 cortisol levels at home, increases were effects may have already been set in
noted in the majority of children (63 motion.
7am 8 9 10 11 12 1pm 2 3 4 5 percent) at day care, with 40 percent And the negative effects of day care
Time of Day classified as a stress response.” may be long lasting. A large-scale
The HPA axis and the immune study in 2009 involving nine
Fig. 3. Compared to cortisol levels at home, increases were system are functionally linked. A institutions followed approximately
noted in the majority of children (63%) at home-based day
care, with 40% classified as a stress response, even in day recent study at Cornell University 1,000 children from the age of one
care homes where there were only one or two children therefore examined both cortisol month through mid-adolescence
(see Gunnar et al. 2010). levels and antibody secretion among to examine the effects on later
Vol 58 No 3 THE BIOLOGIST 31B ENDOCRINOLOGY
THE BIOLOGICAL EFFECTS OF DAY CARE
development of childcare in the programming and its effects may be the effects of day care on the child
first few years of life. Researchers subtle but this does not preclude their continues to be discussed through
observed children in and out of their Understanding significance. If cortisol exposure can the prism of adult sexual politics
homes, and when they reached 15 the effects of be neurotoxic, with adverse effects on and women’s rights. This has been
years-old, they measured their day care on the both specific neurons and entire a significant impediment, involving
awakening cortisol levels. child continues neural systems, and some children a serious conflict of interest: women’s
Children who spent more time in to be discussed are experiencing elevated cortisol rights and self-fulfillment are not
centre-based childcare during their through the levels at day care during the first the same issue as child wellbeing and
first three years — whether care of prism of adult three years of life when the brain will may often compete for precedence.
high or low quality — “were more sexual politics reach approximately 80 percent of its If women’s rights have been hard
likely to have the atypical pattern and women’s adult size, any consideration of day won, so too has the ability to publish
of lower levels of cortisol just after rights care attendance must take these and discuss openly the inconvenient
awakening when they were 15 years of factors into account. Since the effects of day care on children.
age, which could indicate higher structure At the same time, curiously, there
levels of early stress.” and function of the brain are still appears to be little effort invested
Abnormal cortisol patterns were developing in children, failure to in concern over the feelings of
observed regardless of gender or find consistent HPAA abnormalities stay-at-home mothers. As it
ethnicity, the family’s income level, associated with day care does not stands, parental care and day
the mother’s level of education or the preclude the importance of these care are presented as equal
degree of sensitivity exhibited by systems (Mash and Wolf 2010). alternatives entailing mere
parents during the child’s teenage And modern life is throwing up stylistic differences and choices.
years. It is thought that these children further related, if inconvenient, Biologically-based research
may be more prone to stress in their findings. Early child-rearing is now providing a very
teenage years (Roisman et al. 2009). environment and a less secure different perspective.
infant-mother attachment are now No matter how uncomfortable,
Quality of care and cortisol associated with earlier puberty in society now needs an honest
The so-called “quality of care” has girls (Belsky et al. 2010), as is absence framework in which to make
been found to modulate some of of the biological father. Deardoff et al. decisions about childcare. Yet there
the relationship between day (2010) found this to be the case only remains a lack of acknowledgment for
care attendance and cortisol among higher income families and a dose-response relationship: not just
dysregulation. In the study above posited that “higher income families the ‘quality’ of day care, but the
by Groenveld et al. (2010), lower without fathers are more likely to number of hours spent in day care
caregiver sensitivity was associated have a single mother who works long and the age of initiation may affect
with higher levels of cortisol during hours and is not as available for children. It’s almost certainly not
the day in home-based childcare. In caregiving.” The study pointed to a case of more being merrier.
centre-based childcare, lower global “neuroendocrine pathways that Biology has a vital yet under-
quality of care was associated with an influence development”, especially recognised contribution to make in
increase in cortisol between 11:00am cortisol release. this important area of family life and
and 3:00pm. They concluded: While understanding the effects of national policy. In future, when
“Quality of care is an important childcare involves more than a policy-making bodies take evidence,
factor in young children’s wellbeing consideration of neuroendocrine biology should be there in the witness
and HPA stress reactivity.” studies, research from the biological box enabling both governments and
The above study on home-based sciences continues to be under- society at large to make more fully
day care by Gunnar et al. (2010) also reported and under-recognised. informed decisions. Increased
found that increases in cortisol levels However, what is often widely funding for biological research in this
throughout the day were influenced reported and recognized can be area is therefore vital.
by the care provider and activities. found in a recent headline: “Day Ultimately, decisions about
The researchers say “the behaviour of care Does Not Cause Academic or childcare must not be made based
the care provider is associated with Behaviour Problems” (Walsh 2010). upon the limited nature of “evidence-
both how well children function at The lead researcher of the study based research”. Many fundamental
childcare, and how much their in question is quoted in the press aspects of a child’s developmental
cortisol is elevated”. release from the publisher, the wellbeing are not accessible through
American Psychological Association: current methods of assessment
Discussion “Overall, I think this shows women because they are simply too
It seems clear that early who go back to work soon after they nuanced or unsuitable.
childcare experiences are have their children should not be too And so, as we embrace early day
associated with endocrine concerned about the effects their care ever further, we should remind
changes in the HPAA. The employment has on their children’s ourselves that when it comes to an
process of long-term well-being.” (APA 2010; issue of such fundamental
HPAA Lucas-Thompson et al. 2010). importance we must continue to
Academic achievement and adhere to that ancient medical
overt behavioural problems imperative “First do no harm”, and
are highly prominent assume that mother knows best.
outcome measures, while
biological variables are not. More reading and references at
Unfortunately, understanding www.societyofbiology.org/biologist
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