Cortisol levels of infants in center care across the first year of life: links with quality of care and infant temperament

Figures & data

Table 1. Means and standard deviations for the (variables constituting the composite) predictors of inter-individual differences in infant cortisol concentrations in center care.

	n	M	SD	Min	Max
Maternal age (years)	64	35.00	3.21	27.46	43.23
Maternal educational level (%)	64
Elementary education	0.0
Middle/higher professional  education	53.1
University	45.3
Other	1.6
Maternal depression	64	4.63	3.52	0.00	13.00
Infant negative emotionality	55	.00	1.00	−2.13	2.54
Infant sex (%)
Girl	46.9
Infant age upon entry in  center care (weeks)	64	14.60	2.80	8.86	23.14
Quality of maternal care	64	5.86	1.78	3.00	9.00
Sensitivity week 0	64	5.70	1.92	2.00	9.00
Cooperation week 0	64	6.02	1.80	3.00	9.00
Quality of center care	64	5.26	1.32	2.83	8.33
Sensitivity week 1	64	5.14	1.73	1.00	9.00
Cooperation week 1	64	5.50	1.43	3.00	9.00
Sensitivity week 12	64	5.19	1.70	2.00	8.00
Cooperation week 12	64	5.09	1.75	1.00	9.00
Sensitivity week 24	64	5.27	1.92	1.00	9.00
Cooperation week 24	64	5.34	1.77	1.00	9.00

Variables in italics are used as confounders and predictors in the regression analyses. Scales range from 1 to 9 for the quality of care variables.

Figure 1. Average morning and afternoon cortisol concentrations (nmol/L) in center care across the first 9 months after entering center care at 3 months of age.

Table 2. Raw Means and Standard Deviations for the Cortisol Levels (nmol/L) in Center Care and at Home.

		Child care		Home
	Age (weeks)	Morning	Afternoon	Morning	Afternoon
Week*	M SD	M SD	M SD	M SD	M SD
0		–	–	7.7 (5.0)	6.4 (4.6)
1	14.6 (2.8)	8.5 (6.4)	8.2 (6.7)
2	15.7 (2.9)	8.8 (5.5)	7.6 (6.7)
3	16.8 (3.0)	11.4 (7.7)	7.7 (6.3)
4	18.0 (3.0)	12.0 (8.4)	8.0 (6.4)
8	21.9 (2.9)	10.3 (7.5)	7.8 (6.3)
12	26.0 (3.0)	9.8 (6.9)	6.5 (5.6)
16	30.2 (3.0)	9.1 (7.2)	7.3 (6.3)
24	38.5 (3.3)	8.0 (7.1)	6.2 (5.4)	6.3 (5.6)	5.5 (6.6)
36	52.1 (1.0)	7.2 (5.8)	6.7 (5.8)	5.3 (4.9)	4.3 (5.9)

*Week 0 is the week before entering child care, and weeks 1–36 are weeks after entry.

Table 3. Correlations among the variables predicting infants’ cortisol concentrations in center care.

	1	2	3
1. Infant negative emotionality	–
2. Quality of maternal care	−0.17	–
3. Quality of center care	−0.32*	0.14	–

*p < 0.05 (one-tailed).

Table 4. Results of the longitudinal regression analyses (multilevel) comparing infants’ cortisol concentrations, and cortisol slope, in center care and at home in weeks 1, 24, and 36 after entry in center care.

	Morning cortisol			Afternoon cortisol			Cortisol slope
	10.00 h			16.00 h			10.00–16.00 h
	Estimate	S.E.	p	Estimate	S.E.	p	Estimate	S.E.	p
Fixed effects
Intercept	0.736	0.077	0.000***	0.912	0.152	0.000***	0.063	0.067	0.347
Time linear	−0.005	0.001	0.000***	−0.016	0.004	0.000***	0.000	0.002	0.681
Location (1 = home, 2 = center care)	0.086	0.040	0.033*	−0.072	0.096	0.456
Time × location				0.007	0.003	0.006**
Deviance	361.629			380.185			585.218

p < 0.10, *p < 0.05, **p < 0.01, ***p < 0.001.

Table 5. Results of the longitudinal regression analyses (multilevel) predicting infants’ morning and afternoon cortisol concentrations, and cortisol slope, in center care in weeks 1, 2, 3, 4, 8, 12, 16, 24, and 36 after entry.

	Morning cortisol in center care			Afternoon cortisol in center care			Cortisol slope in center care
	10.00 h			16.00 h			10.00 h–16.00 h
	Estimate	S.E.	p	Estimate	S.E.	p	Estimate	S.E.	p
Fixed effects
Intercept	0.093	0.409	0.820	0.818	0.043	0.000	0.053	0.106	0.617
Time linear	0.099	0.046	0.033*	−0.004	0.001	0.009**	−0.001	0.002	0.715
Time quadratic	−0.004	0.002	0.020*
Time cubic	0.000	0.000	0.017*
Time awake (morning)	0.000	0.000	0.946				0.000	0.000	0.516
Time awake (afternoon)				0.000	0.000	0.943	0.000	0.000	0.451
Time since last feeding (morning)							0.000	0.000	0.321
Infant negative emotionality	0.040	0.021	0.061†	−0.004	0.024	0.856	0.024	0.029	0.414
Quality of maternal care	0.080	0.021	0.000***	0.034	0.024	0.174	0.053	0.030	0.074^†
Quality of maternal care X				0.057	0.022	0.013*
negative emotionality
Deviance	361.629			380.185			585.218

^†p < 0.10, *p < 0.05, **p < 0.01, ***p < 0.00.1.

Figure 2. Interaction effect between infant negative emotionality and maternal quality of care predicting infant afternoon cortisol concentrations in center care.