Early Child Care and Weight Status in a Cohort of Predominantly Black Infants in the Southeastern United States

Abstract

Background:

Previous studies show inconsistent relations between child care and obesity, but few assessed longitudinal associations during infancy and even fewer included racially diverse children. We examined associations of time infants spent in child care, both overall and in different types of care, with weight status at 6 and 12 months.

Methods:

We examined 664 infants living in central North Carolina. We conducted adjusted multivariable linear regressions examining (1) child care from birth to 6 months and 6-month weight-for-length (WFL) z-score, and (2) child care from birth to 12 months and 12-month WFL z-score. We assessed any child care and child care by type, including relative care, informal care by a nonrelative, formal child care, and a combination of care (e.g., relative and informal care).

Results:

Nearly 70% of infants were black and 49% were female. After adjustment for potential confounders, any child care was not associated with WFL z-score at 6 months (0.07; 95% confidence intervals [CI] −0.02 to 0.16; p = 0.13) or 12 months (0.05; 95% CI −0.02 to 0.12; p = 0.19). However, greater combination care was associated with higher WFL z-score at 6 months (0.68; 95% CI 0.23–1.13; p = 0.003) and greater care by a relative was associated with higher WFL z-score at 12 months (0.16; 95% CI 0.05–0.26; p = 0.005).

Conclusions:

Although we did not observe associations with any child care, combination care and relative care during infancy were associated with higher weight. Interventions aimed at preventing excessive weight gain in early life may target relatives who provide regular care for infants.

Introduction

A growing number of children are cared for outside of the home by a nonparental caregiver. As such, many parents share the responsibility of caring for children, especially their young children, with other adults. Child care, or routine care by nonparental adults that takes place within or outside of children's homes, has become increasingly common. In developed countries, nearly one-quarter of children less than 3 years spent time in child care.¹ The types of care vary, including formal care often located in a dedicated building (e.g., center or nursery), informal care by a nonrelative that may take place in the child's home or the caretaker's home (e.g., childminder, family child care home, or nanny), and relative care (e.g., grandparent). Among infants in the United States, nearly 16% spent time in formal child care and ∼35% were cared for by a relative—mainly a grandmother.²

Both the child care setting and the actual caregiver have been identified as potential targets for childhood obesity prevention.^3,4 Child care has been inconsistently associated with obesity in children younger than 6 years.^5–8 Among infants, previous studies have also found mixed results.^9–18 In our prior review of 11 articles examining child care during infancy and later obesity, we found that studies were heterogeneous in defining child care, categorizing child care, and measuring both exposure and outcome.⁷ A slight majority of studies found no association between child care and obesity. Some, however, observed a positive association in that greater child care in infancy was associated with higher rates of obesity later in childhood.⁷

Despite this, most prior studies have been conducted in cohorts of relatively high socioeconomic status families and mainly white infants, whose rates of overweight and obesity have either plateaued or declined in recent years.¹⁹ These signs of improvement are relatively absent for racial and ethnic minority groups, where even very young children are disproportionately burdened by obesity.²⁰ Additionally, infants may be especially vulnerable to nonparental child care, as the first year represents a critical and dynamic time for growth. Therefore, the purpose of this study was to examine associations of child care during infancy, both overall and in different types of care, with weight status at 6 and 12 months in a cohort of predominantly black infants in the southeastern United States. We designed the study to specifically examine this research question. We hypothesized that infants who spent greater time in child care would be heavier than those cared for by parents, and that this association would be strongest for infants in informal care settings.

Methods

Study Sample

Nurture is a birth cohort study of mothers and infants residing in North Carolina in the southeastern United States.²¹ The goal of the Nurture study was to evaluate associations between nonparental child care and infant weight status. Between 2013 and 2015, we enrolled women in later pregnancy, reconsented them shortly after birth, and conducted home visits when infants were 3, 6, 9, and 12 months of age. In addition, women received automated interactive voice response telephone calls in months 1, 2, 4, 5, 7, 8, 10, and 11 to assess child care, breastfeeding, and introduction to solid foods. Additional information about Nurture is available elsewhere.²¹ The procedures followed were in accordance with the ethical standards of the responsible committee on human experimentation (institutional and national) and with the Helsinki Declaration of 1975, as revised in 2008. The Duke University Medical Center Institutional Review Board approved this study.

Briefly, we recruited women from a private prenatal clinic and the local county health department prenatal clinic. To participate, pregnant women were required to be 20–36 weeks' gestation, be pregnant with a singleton with no known congenital abnormalities, be 18 years or older, speak and read English, intend to keep their infants, and plan to stay within the area for at least 12 months. At birth, we further excluded infants who were born before 37 weeks' gestation (thus all infants in our sample were full term and there was no upper limit on gestational age), had congenital abnormalities that could affect growth, were in the hospital for 3 or more weeks after birth, or were not able to take food by mouth at discharge. Of the 666 women who enrolled their infants, 535 (80.3%) completed the home visit at 3 months, 497 (74.6%) at 6 months, 457 (68.6%) at 9 months, and 468 (70.3%) at 12 months. We excluded two infants who were no longer in the care of their mothers. We further excluded infants with missing data on the exposure, outcome, or covariates, leaving an analysis sample of 494 infants at 6 months and 449 infants at 12 months.

We compared the excluded sample to the full sample of 664 infants and observed some differences. In the excluded sample, 69.2% of infants were black, versus 64.5% in the full sample (p = 0.002). Infants in the excluded sample were breastfed for a mean (standard deviation [SD]) of 3.4 (4.2) months, compared with the full sample of 4.2 (4.5) months (p < 0.001). Among mothers, 47.7% in the excluded sample had a high school diploma or less, compared with 42.6% of mothers in the full sample (p = 0.002). The mean (SD) prepregnancy BMI was 29.8 (9.3) and 30.7 (9.5) in the excluded versus the full sample, respectively (p = 0.001). We did not observe differences in infant birth weight for gestational age z-score, maternal marital status, or household income.

Exposure

We prospectively assessed child care each month. Mothers reported nonparental child care of their infants as any care occurring for three or more hours per week by someone other than a parent on a regular basis. We computed the number of weeks of any care combined as a continuous variable, defined as any week in which at least 3 hours of nonparental care took place from birth to 6 months and birth to 12 months. We also calculated specific types of care using this same criterion, including care by a relative, informal care by a nonrelative, formal care by a nonrelative, and a combination of care (i.e., relative and informal care, relative and formal care, or informal and formal care).

Outcome

Trained research assistants measured infant weight and length in triplicate during the 6- and 12-month home visits and used an average of the three measurements using standard techniques.²² Research assistants measured infant recumbent length without shoes using a ShorrBoard Portable Length Board to the nearest 1/8 inch. They measured infants in light clothing without shoes using a Seca Infant Scale to the nearest 0.1 pound. We calculated 6- and 12-month weight-for-length (WFL) z-score using World Health Organization age- and sex-specific reference data.²³

Other Measures

We collected demographic information from mothers through questionnaires at recruitment, at birth, and during each home visit. Maternal and household variables included age, education (≤high school graduate, and more than high school), marital status, and prepregnancy BMI as a continuous variable (extracted from the medical record), and annual household income (≤$20,000 or >$20,000). For infants, we abstracted information on birth length in centimeters and birth weight in grams from the medical record. We calculated birth weight for gestational age z-score using reference data from Intergrowth-21st Newborn Birth Weight Standards and z-scores.²⁴ We prospectively assessed breastfeeding (any breastmilk fed through breast or bottle) and age at introduction to solid foods each month. We calculated the total number of months of any breastfeeding and the age in months when infants were first introduced solid foods.

Analysis

We conducted multivariable linear regressions examining any child care from birth to 6 months and WFL z-score at 6 months as the outcome and any child care from birth to 12 months and 12-month WFL z-score as the outcome. Secondarily, we examined type of child care as relative care, informal care by a nonrelative, formal care, and a combination of care with weight outcomes at 6 and 12 months. Thus, we computed a dose/effect by both overall and type of care, treating children with varying amounts of care differently. Additionally, infants who spent time in multiple types of care contributed to each exposure. We adjusted for covariates that were of a priori interest based on prior literature,⁷ including infant age, gender, race, birth weight for gestational age z-score, breastfeeding duration, and early introduction of solid foods (before 4 months of age); maternal age, education, marital status, and prepregnancy BMI; and household income. We report adjusted estimates per each additional 10 hours of care each week. We present results as parameter estimates, 95% confidence intervals (CI), and two-sided p-values. We conducted all analyses using R version 3.3.1 (R Foundation for Statistical Consulting, Vienna, Austria) at a significance level of <0.05.

Results

Of the 664, just under half of mothers (47.7%) had a high school diploma or less, 59.8% were married or living with a partner, and 60.7% had household incomes ≤ $20,000 per year (Table 1). Nearly 70% (69.2%) of infants were black and 48.8% were female. The mean (SD) birth weight for gestational age z-score was −0.3 (0.9). Infants were breastfed for a mean (SD) of 3.4 (4.2) months and 41.0% were introduced to solid foods before 4 months. Among the analytic sample, 114 infants at 6 months and 174 infants at 12 months were cared for exclusively by a parent and did not receive any type of child care. At 6 months, 226 were cared for by relatives, 53 were in informal care, and 101 in formal care. At 12 months, 171 were cared for by relatives, 34 were in informal care, and 70 in formal care. Additionally, 43 received a combination of care during the first 6 months and 70 received a combination of care over 12 months.

Table 1.

Demographic Characteristics of Mothers and Infants in the Nurture Study (n = 664)

Infant characteristics	Mean (standard deviation)
Birth weight for gestational age z-score	−0.3 (0.9)
Breastfeeding duration, months (n = 449)	3.4 (4.2)
Child care, hours per week (n = 449)	12.2 (14.8)
Relative care (n = 449)	6.4 (10.8)
Informal care (n = 449)	1.4 (4.6)
Formal care (n = 449)	6.6 (9.9)
Weight-for-length z-score at 6 months (n = 494)	0.4 (1.1)
Weight-for-length z-score at 12 months (n = 449)	0.6 (1.0)
	Percent (number)
Gender, female	48.8 (324)
Race
Black	69.2 (459)
White	15.4 (102)
Other race/more than one race	15.4 (102)
Ethnicity, Latino/a	9.4 (59)
Entered child care within first 3 months (n = 494)	33.9 (180)
Introduced solid foods before 4 months (n = 494)	41.0 (229)
Maternal characteristics	Mean (standard deviation)
Age, years	27.3 (5.8)
Prepregnancy BMI, kg/m²	29.8 (9.3)
	Percent (number)
Marital status
Married or living with partner	59.8 (395)
Never married, divorced, separated, other	40.2 (265)
Race
Black	71.7 (474)
White	19.4 (128)
Other race/more than one race	8.9 (59)
Ethnicity, Latina	6.5 (43)
Education
≤High school graduate	47.7 (316)
Some college/college or graduate degree	52.3 (347)
Household characteristics	Mean (standard deviation)
Number of adults in the household	3.7 (2.9)
Number of children in the household	1.3 (1.6)
	Percent (Number)
Annual household income
≤ $20,000	60.7 (368)
> $20,000	39.3 (238)

After adjustment for potential confounders, any type of child care combined from birth to 6 months was not associated with WFL z-score at 6 months (0.07 units per each additional 10 hours per week of care; 95% CI −0.02 to 0.16; p = 0.13) (Table 2). Similarly, any child care from birth to 12 months was not associated with WFL z-score at 12 months (0.05; 95% CI −0.02 to 0.12; p = 0.19). Some covariates identified a priori were significant predictors of WFL z-score in the 6- and 12-month models, including maternal prepregnancy BMI and birth weight for gestational age z-score.

Table 2.

Adjusted Estimates and 95% Confidence Intervals for Associations of Child Care from Birth to 6 Months and 6-Month Weight-for-Length z-Score and Child Care from Birth to 12 Months and 12-Month Weight-for-Length z-Score, Overall and By Type of Care

	6-Month weight-for-length z-score		12-Month weight-for-length z-score
	Estimate (95% CI)	p	Estimate (95% CI)	p
Any child care	0.07 (−0.02 to 0.16)	0.13	0.05 (−0.02 to 0.12)	0.19
Relative care	0.08 (−0.04 to 0.21)	0.18	0.16 (0.05 to 0.26)	0.005
Informal care	0.10 (−0.18 to 0.39)	0.13	0.05 (−0.17 to 0.27)	0.68
Formal care	−0.11 (−0.25 to 0.03)	0.12	−0.02 (−0.13 to 0.08)	0.67
Combination care	0.68 (0.23 to 1.13)	0.003	−0.13 (−0.45 to 0.20)	0.44

Adjusted for infant age, gender, race, birth weight for gestational age z-score, early introduction to solid foods, and breastfeeding duration; maternal age, education, marital status, and prepregnancy BMI; and household income.

CI, confidence intervals.

When we examined each type of care, greater combination care was associated with higher WFL z-score at 6 months (0.68; 95% CI 0.23–1.13; p = 0.003) but not at 12 months (−0.13; 95% CI −0.45 to 0.20; p = 0.44). Due to small cell sizes, we were not able to examine the effect of specific combinations of care. Additionally, care by a relative from birth to 6 months was not associated with WFL z-score at 6 months (0.08; 95% CI −0.04 to 0.21; p = 0.18). However, child care from birth to 12 months was associated with a 0.16 unit increase in WFL z-score at 12 months (95% CI 0.05–0.26; p = 0.005). In our study, grandparents provided more than two-thirds of the relative care for infants. None of the other types of care was associated with WFL z-score at 6 or 12 months.

Discussion

In this cohort of predominantly black infants living in the southeastern United States, we did not observe associations between any child care combined and later infant weight status. However, when we examined specific types of care, combination care at 6 months and greater care by a relative at 12 months was associated with higher weight status in infants. The effect of relative care may need to accumulate throughout infancy before an association with weight emerges. We did not observe associations between the other types of care and infant WFL z-score.

Prior studies have assessed longitudinal associations of infant child care and later obesity and yielded inconsistent results.^9–18 These studies, however, did not uniformly categorize types of care. For example, some researchers defined informal care to include licensed and paid care in a home, whereas others defined informal care as nonlicensed and nonpaid care by relatives. Despite these differences, of the five studies that examined informal child care and later obesity, all but one observed positive significant associations in that greater care in hours or duration was associated with higher weight.^{9,10,12,17,18} Three of these studies found a relationship between care by grandparents and later obesity and thus, the authors identified grandparents as a potentially problematic and perhaps obesogenic provider of care for infants.^12,17,18

Moreover, a recent study in China highlighted grandparents as an important contributing factor to childhood obesity.²⁵ However, in another study of elementary school children in the United States, grandparents appear to have played a protective role against obesity for some children of Hispanic descent.²⁶ The findings from China are consistent with our results, as most relatives caring for infants in our sample were grandparents. This may be due to generational differences in feeding practices. Recent studies highlighted the extent to which grandparents are often responsible for feeding children meals and snacks,^27,28 and their potential role in the development of obesity.²⁹ One prior study found that both tension and conflict existed between parents and grandparents related to child feeding.²⁸ Grandparents may be more likely to indulge children with less healthy foods, to overfeed, and to perceive heavy children as healthy children.²⁵ There is further evidence that preschoolers cared for by relatives were more likely to be obese, compared with children in other care arrangements, although grandparent care specifically was not examined.^30–32

Country of origin, racial and ethnic composition of the sample, and family socioeconomic status may also explain some of the differences among studies. Most cohorts examined in prior studies included white infants only. Three previous studies included some black infants, but at a relatively low percentage (range of 3%–16%).^10,12,13 Additionally, three studies took place in the United States, with the remaining studies conducted in Canada, China, Denmark, Finland, Hong Kong, Ireland, and the United Kingdom. Maternity leave and breastfeeding rates differ substantially among these counties and both factors may affect associations of child care and obesity. For instance, in a US study mothers who returned to work and placed their infants in nonparental child care were more likely to discontinue breastfeeding.³³ Furthermore, use of informal child care has been associated with a reduced likelihood of breastfeeding.³⁴ In the present analysis, we included any breastfeeding as a covariate in adjusted analyses, rather than exclusive breastfeeding, because of the low number who exclusively breastfed. Family socioeconomic status may also play a role; children from higher resource families may be more negatively affected, in terms of obesity risk, by child care outside of the home.^6,9 We were not able to examine differences by socioeconomic status, however, because the ranges of both income and maternal education in our cohort were relatively narrow. Additionally, and as noted above, many of the prior studies were conducted outside of the United States. Cultural differences related to child care norms and expectations may explain the inconsistencies in findings.

Unlike previous studies, where the authors conducted secondary analyses using data from existing cohorts with varying study aims, however, the Nurture study was designed primarily to investigate the association between child care and obesity. As such, we conducted more detailed assessments of child care attendance. Women bear the primary responsibility for caring for infants, and the cost of child care outside of the home has increasingly become a financial burden.^35,36 There is some evidence that reducing child care costs³⁷ and being in close proximity to grandmothers could increase maternal employment.³⁸ Child care arrangements also fluctuate in the postpartum period so we prospectively assessed child care exposure each month over the first year of life. Thus, our assessments of nonparental child care were more frequent and designed to assess the evolving and sometimes inconsistent nature of child care throughout infancy. However, a large proportion of infants were exclusively cared for by a parent, which may reflect the economic trends of the time; unemployment rates in the United States were relatively high at the time of the study. We also were not able to examine specific combinations of care (e.g., infants in both formal child care and relative care) due to small cell sizes.

There are other limitations. First, Nurture participants were not entirely representative of the general population in North Carolina. Women attended one of two obstetric clinics; one clinic cared for a large proportion of higher-income, non-Hispanic white women with high-risk pregnancies and the second served a high percentage of low-income women. The demographic composition of our sample included a higher representation of black women than the local population. This limits the generalizability of our findings. Second, as with most cohorts, attrition was an issue. From birth to 12 months, about 29% of mothers withdrew or were lost to follow-up. This retention rate is not unusual.^39,40 In a similar birth cohort from the same geographic region in North Carolina, for example, attrition rates at the 12-month follow-up were 56%.³⁹ Third, as noted in our previous study, families with some unmeasured attribute that may itself be related to obesity may be more likely to choose relative care for their infants.¹⁰ This could explain our findings and further, we do not attempt to draw any conclusions about causality. Finally, we did not assess weight status beyond 12 months, although we plan to continue to follow these children into childhood and beyond.

In summary, we found that care by a relative, mainly by grandparents, was associated with higher weight status in infants at 12 months. The coefficient estimates we observed were small, but could still be clinically meaningful. For example, for an average female infant at 12 months in Nurture, a 0.16 unit difference in WFL z-score, the estimate we observed at 12 months for relative care, this translates to moving from approximately the 60th to about the 68th percentile on the World Health Organization growth charts. Additionally, if the trajectory persists into early childhood (and beyond), the cumulative effect of relative care could have a substantial impact on later weight. Infancy may therefore be a critical period for intervention, and relatives may be a primary target.

Funding Information

This study was supported by a grant from the National Institutes of Health (R01DK094841). The funders had no role in the design of the study, data collection and analysis, decision to publish, or preparation of the article.

Footnotes

Author Disclosure Statement

No competing financial interests exist.

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