Childcare Environment and Japanese Children Who Are Overweight in Early Childhood

Abstract

Background:

Maternal employment may affect child care styles and contribute to the increasing prevalence of overweight children. We explored the potential risk factors for becoming overweight during early childhood, especially in the child care environment.

Methods:

We conducted a retrospective cohort study using data from health check-up services from 2007 to 2015 in Kobe, Japan. The main outcome was being overweight at age 3 years, which was defined by the International Obesity Task Force cutoffs. Environmental, maternal, and infantile factors were examined as possible risk factors for childhood overweight.

Results:

Of 31,463 infants, 1315 (4.2%) were classified as overweight at age 3 years. Compared with children who were cared for by their mothers during the day at 4 and 18 months, the adjusted odds ratio (aOR) for becoming overweight for those who were not cared for by their mothers was 1.52: 95% confidence interval (CI), 1.16–1.99. Long sleep duration was associated with lower risk of childhood overweight: aOR, 0.79; 95% CI, 0.66–0.96.

Conclusion:

Less daytime care by mothers and shorter sleep duration were associated with increased risk of becoming overweight during childhood. Further studies are needed to determine on how the effect of those factors may be diminished with respect to childhood overweight.

Introduction

In recent decades, the prevalence of overweight young children has increased worldwide.^1–4 From 1980 to 2013, the prevalence of overweight children has increased from 1.5% to 22% in developed countries.⁴ Similarly, an increasing trend was observed in Japan; from 1985 to 2015, the prevalence of overweight 6-year-old children rose from 1% to 3%.⁵ Children who are overweight or obese in the preschool period are more likely to be so during adolescence.⁶ They are also at greater risk for numerous comorbidities in later life, such as cardiovascular disease and type 2 diabetes.⁷ Therefore, being overweight in childhood is a significant health issue.

Various risk factors for childhood overweight or obesity have been identified. With respect to family characteristics, parental obesity is reported as an important risk factor for obesity during childhood.⁸ Excessive maternal weight gain, and maternal smoking during pregnancy also increase childhood overweight.⁹ Unhealthy feeding habits of parents or carers affect their children's dietary intake, and lead to childhood obesity.¹⁰ In terms of infantile factors, the risk of obesity in childhood rises with increasing birth weight.⁸ Some factors regarding lifestyle in early childhood, such as short sleep duration,¹¹ watching television longer,⁸ and increased intake of sugar-sweetened beverages,¹² are reported as potential risk factors of childhood obesity.

In developed countries, including Japan, more and more women with young children have entered the workforce in recent decades.^13,14 This may have resulted in changing child care environment and children's life habits and led to more children who are overweight or obese.

This study explored potential risk factors associated with overweight during early childhood, including type of child care, using a large population-based sample in Kobe, Japan. We undertook this study for the following reasons: (1) the child care environment could be modifiable; (2) there is inconsistency between previously reported results, especially in the association between maternal child care and childhood obesity.^15–20

Patients and Methods

Study Design, Setting, and Participants

This was a population-based, retrospective cohort study; we used records from an infant health checkup service in Kobe. Kobe is Japan's sixth-largest city and has a population of over 1.5 million. Over 12,000 infants are born in that city annually.²¹ The Kobe city government provides data from health checkups to all expectant mothers and infants; that is, in fact, obligatory for all local governments in Japan. The health checkup service in Kobe consists of public health nurses visiting mothers and infants within 4 months after birth. In addition, pediatricians conduct physical and developmental examinations; self-report data are collected at municipal ward healthcare service offices or by designated home physicians about child and family life habits.

We used anonymous health checkup data for infants born from April 1, 2007 to March 31, 2012 in Kobe. Infants with data for all the checkup services (early infancy up to age 4 months and at 4, 9, and 18 months and 3 years) were included in this study. Infants were excluded if they were born before 35 weeks of gestation, had a birth weight of <2000 g, or had any physical and/or developmental problems requiring regular follow-up or treatment (except for being underweight, overweight, or obese). We also excluded subjects with missing or partial physical measurements or type of child care data. The study protocol was approved by the Ethics Committee of Kyoto University, Graduate School and Faculty of Medicine (E0339).

Outcome Measure

At each checkup, trained public health nurses measured the infants' height and weight (without shoes and clothing). Infant weight was recorded in grams as integers; infant height was determined in centimeters to one decimal place. The primary outcome measure was being overweight (including obesity) at 3 years of age. Overweight was defined by the International Obesity Task Force cutoffs for BMI,²² which were >17.89 for boys and >17.56 for girls at 3 years. Obesity is a more severe status than being overweight (BMI >19.57 for boys and >19.36 for girls at 3 years). We did not examine obesity as a separate outcome since its prevalence was expected to be low in Japan.

Exposure and Candidate Risk Factors

The following environmental factors were considered as candidate risk factors for children becoming overweight during early childhood: type of child care; support of child care from partners, parents, and step-parents; family members who smoke; presence of older siblings; sleep duration [categorized based on the wake-up time and bedtime as shown in Supplementary Table S1 (Supplementary Data are available online at www.liebertpub.com/chi); naps were not included]; breastfeeding duration; age when solid foods were induced; regular mealtimes; use of precooked foods; consumption of cow's milk; and consumption of sugar-sweetened beverages. Questions regarding infants' eating and sleeping habits were asked at 18 months; exceptions were breastfeeding duration and timing of solid food induction—both of which were queried at 9 months.

With respect to the type of child care, we focused on the length of time that mothers were the infant's primary daytime we assessed through the questionnaire item “Who mainly takes care of the child during the daytime?” We asked that question at ages 4 and 18 months. We considered that a large majority of mothers would take care of the children for a certain period after birth; then, some mothers would entrust the children to their grandparents, babysitters, or a child care nursery. We therefore considered that we could estimate the duration of maternal child care by the response to that question.

We categorized the participants into three groups in terms of maternal child care. The groups were as follows: daytime child care provided mainly by mothers at (1) both 4 and 18 months (both-mother group); (2) daytime child care mainly provided by mothers at either 4 or 18 months (either-mother group); and (3) daytime child care mainly provided by mothers at neither 4 nor 18 months (neither-mother group). In the either-mother group, we did not expect most children to be mainly cared for by the mother at 4 months; thus, we did not distinguish between children who were not cared for by the mother at 4 months and those not cared for by the mother at 18 months.

Since several studies have reported an association between maternal employment and overweight children,^17–20 we performed a subgroup analysis within the neither-mother group to investigate the influence of day care by relatives and nonrelatives on children becoming overweight. According to the care time by other relatives (including grandparents and fathers), we divided the neither-mother group into the following three subgroups: relative child care (1) at both 4 and 18 months (both-relative group); (2) relative child care at either 4 or 18 months (either-relative group); and (3) relative child care at neither 4 or 18 months (neither-relative group).

In addition, we considered maternal factors, including maternal age at infant's birth, smoking and alcohol consumption during pregnancy, and pregnancy-induced hypertension. We also assessed infant factors, including gestational age, birth weight, sex, and medical history of allergic diseases. We obtained almost all of this information from parental reports.

Statistical Analysis

Descriptive statistics, including percentages for the categorical variables and medians for the continuous variables, were conducted. The distribution of variables was compared using analysis of variance, chi-square test, or Fisher's exact test, as appropriate.

Odds ratios with 95% confidence intervals (CIs) were used to examine the effect of the risk factors on the incidence of children becoming overweight. Other potential risk factors were adjusted through multiple logistic regression models. Wald tests were used to obtain p-values. All reported p-values were two-tailed; p-values <0.05 were considered statistically significant. p-Values were not adjusted for multiple comparisons since we considered this study exploratory. R (version 3.1.2)²³ was used for all analyses.

Results

Participant Characteristics

A total of 41,660 infants completed all the checkup services and were included in this study. According to the Kobe census,²¹ ∼64,000 babies were born in that city from 2007 to 2011; during that period, ∼65% of the target population was included in the present study. Of the 41,660 initial participants, 10.197 infants were excluded (Fig. 1); thus, 31.463 infants were included in the final analysis. The baseline characteristics of the included and excluded participants are described in Supplementary Table S2.

Figure 1.

Flow chart of participant recruitment.

Of the 31.463 infants, 1315 (4.2%) were classified as overweight or obese at age 3 years according to International Obesity Task Force cutoffs for BMI. Table 1 shows the baseline characteristics of subjects who were overweight and those who were not at age 3 years. A total of 19,965 infants (63%) were in the both-mother group, 10,073 (32%) in the either-mother group, and 1425 (5%) in the neither-mother group. The prevalence of overweight infants at age 3 years was 3.7% in the both-mother group, 4.9% in the either-mother group, and 5.8% in the neither-mother group. Supplementary Tables S3 and S4 present, respectively, the distribution of day care providers at 4 and 18 months and the baseline characteristics of the children according to the duration that the mothers were the primary daytime caregivers. Table 1 also details the prevalence of overweight defined by WHO Child Growth Standards at 4 and 18 months and 3 years.²⁴ The bivariate analysis indicated that the distribution of the following factors was significantly different among children who were overweight at 3 years and those who were not: type of child care at 4 and 18 months; maternal smoking during pregnancy; birth weight; sex; sleep duration; and consumption of cow's milk (Table 1).

Table 1.

Baseline Characteristics of the Participants

	All included	Overweight at 3 years	Not overweight at 3 years
	N = 31,463	N = 1315	N = 30,148	p
Outcomes
Median (IQR) BMI at 3 years	15.7 (15.0–16.4)	18.2 (17.9–18.6)	15.6 (14.9–16.3)	<0.001
Overweight (WHO criteria),^a n (%)
At 4 months^b	1032 (3.3)	203 (15)	829 (2.8)	<0.001
At 18 months^b	682 (2.2)	205 (16)	477 (1.6)	<0.001
At 3 years	451 (1.4)	451 (34)	0 (0)	<0.001
Obesity at 3 years, n (%)	93 (0.3)	93 (7.1)	—	<0.001
Environmental factors
Primary day care provider at 4 months, n (%)				0.008
Mother	29,172 (93)	1196 (91)	27,976 (93)
Father	20 (0.1)	0 (0)	20 (0.1)
Grandparents	1459 (4.6)	65 (4.9)	1394 (4.6)
Relatives	138 (0.4)	10 (0.8)	128 (0.4)
Child care nursery	303 (1.0)	23 (1.7)	280 (0.9)
Babysitter	240 (0.8)	16 (1.2)	224 (0.7)
Other	131 (0.4)	5 (0.4)	126 (0.4)
Primary day care provider at 18 months, n (%)				<0.001
Mother	20,831 (66)	780 (59)	20,051 (67)
Father	25 (0.1)	0 (0)	25 (0.1)
Grandparents	1459 (4.6)	44 (3.3)	1415 (4.7)
Relatives	130 (0.4)	10 (0.8)	120 (0.4)
Child care nursery	8851 (28)	472 (36)	8379 (28)
Babysitter	32 (0.1)	0 (0)	32 (0.1)
Other	135 (0.4)	9 (0.7)	126 (0.4)
Support from partner,^b n (%)	28,427 (92)	1180 (92)	27,247 (92)	0.70
Support from parents, n (%)	23,045 (73)	966 (74)	22,079 (73)	0.88
Support from step-parents, n (%)	12,818 (41)	514 (39)	12,304 (41)	0.22
Smoking family members,^b n (%)	12,003 (38)	520 (40)	11,483 (38)	0.29
Older siblings,^b n (%)	16,374 (52)	678 (52)	15,696 (52)	0.74
Breastfeeding until 9 months,^b n (%)	20,039 (64)	807 (61)	19,232 (64)	0.08
Introduction of solid foods,^b n (%)				0.39
Early (≤4 months)	872 (2.8)	42 (3.3)	830 (2.8)
Middle (5–6 months)	27,122 (88)	1116 (87)	26,006 (88)
Late (≥7 months)	2893 (9.4)	130 (10)	2763 (9.3)
Regular mealtime,^b n (%)	29,363 (94)	1220 (93)	28,143 (94)	0.26
Use of precooked foods, n (%)	21,868 (70)	920 (70)	20,948 (70)	0.74
Cow milk consumption, n (%)	22,110 (70)	958 (73)	21,152 (70)	0.04
Sugar-sweetened beverage consumption, n (%)	11,980 (38)	534 (41)	11,446 (38)	0.06
Consumption of sweets or snacks,^b n (%)				0.62
Never	887 (2.9)	39 (3.0)	848 (2.8)
Regular	21,882 (70)	924 (71)	20,958 (70)
Irregular	8298 (38)	331 (26)	7967 (27)
Sleep duration,^c n (%)				<0.001
Short	7700 (25)	375 (29)	7325 (24)
Middle	15,776 (50)	654 (50)	15,122 (50)
Long	5212 (17)	184 (14)	5028 (17)
Irregular	2761 (9)	101 (8)	2660 (9)
Maternal factors
Median (IQR) maternal age at delivery (years)	31 (28–35)	31 (28–35)	31 (28–35)	0.92
Maternal smoking during pregnancy,^b n (%)	1153 (3.7)	62 (4.8)	1091 (3.7)	0.04
Maternal alcohol consumption during pregnancy,^b n (%)	5567 (18)	257 (20)	5310 (18)	0.07
Pregnancy-induced hypertension, n (%)	571 (1.8)	23 (1.7)	548 (1.8)	0.94
Infantile factors
Gestational age, n (%)				0.11
Full-term (≥39 weeks)	21,186 (67)	854 (65)	20,332 (67)
Early-term (37–38 weeks)	9212 (29)	419 (32)	8793 (29)
Preterm (35–36 weeks)	1065 (3.4)	42 (3.2)	1023 (3.4)
Birth weight, n (%)				<0.001
Low (2000–2499 g)	2065 (6.6)	48 (3.7)	2017 (6.7)
Normal (2500–3999 g)	29,188 (93)	1238 (94)	27,950 (93)
Heavy (≥4000 g)	210 (0.7)	29 (2.2)	181 (0.6)
Female, n (%)	15,827 (50)	823 (63)	15,004 (50)	<0.001
Past medical history of allergic diseases,^d n (%)	3486 (12)	141 (12)	3345 (11)	0.80

Defined by the WHO criteria; >20.3 for boys and >20.0 for girls at 4 months; >19.0 for boys and >18.8 for girls at 18 months; >18.4 at 3 years.

Data missing for <2% of infants.

Defined as Supplementary Table S1.

Data missing for 9% of infants.

IQR, interquartile range.

Risk Factors for Being Overweight

Among environmental factors, we found the less time infants spent in maternal day care to be associated with higher risk of being overweight at 3 years. The adjusted odds ratios for children being overweight compared with the both-mother group were 1.23 (95% CI, 1.07–1.42; p = 0.004) in the either-mother group and 1.52 (95% CI, 1.16–1.99; p = 0.003) in the neither-mother group.

We also found that several infantile factors were associated with increased risk for becoming overweight: they included preterm birth, heavier birth weight, being female, and consuming sugar-sweetened beverages. The adjusted odds ratios are described in Table 2. Children having long sleep were less likely to become overweight at age 3 years: adjusted odds ratio compared with the middle category as reference, 0.79; 95% CI, 0.66–0.96.

Table 2.

Factors Associated with Children Being Overweight at Age 3 Years

	aOR	95% Confidence interval	p
Environmental factors
Maternal day care
Both at 4 and 18 months	1 (Reference)
Either at 4 or 18 months	1.23	1.07–1.42	0.004
Neither at 4 nor 18 months	1.52	1.16–1.99	0.003
Support from partner	1.17	0.92–1.49	0.20
Support from parents	0.98	0.86–1.13	0.83
Support from step-parents	0.98	0.86–1.11	0.74
Smoking family members	0.99	0.87–1.13	0.91
Older siblings	0.93	0.82–1.06	0.29
Sleep duration^a
Short	1.10	0.95–1.28	0.19
Middle	1 (Reference)
Long	0.79	0.66–0.96	0.02
Irregular	0.73	0.51–1.06	0.10
Breastfeeding until 9 months	0.99	0.87–1.14	0.93
Introduction of solid foods
Early (≤4 months)	1.11	0.78–1.60	0.56
Middle (5–6 months)	1 (Reference)
Late (≥7 months)	1.14	0.92–1.41	0.22
Regular mealtime	0.86	0.64–1.14	0.29
Use of precooked foods	1.01	0.88–1.16	0.90
Consumption of cow's milk	1.09	0.94–1.26	0.26
Consumption of sugar-sweetened beverages	1.14	1.00–1.29	0.05
Consumption of sweets or snacks
Never	1.17	0.80–1.69	0.42
Regular	1 (Reference)
Irregular	0.97	0.83–1.14	0.74
Maternal factors
Maternal age at delivery (years)	1.00	0.99–1.01	0.98
Maternal smoking during pregnancy	1.23	0.88–1.71	0.23
Maternal alcohol consumption during pregnancy	1.13	0.97–1.32	0.12
Pregnancy-induced hypertension	0.97	0.61–1.55	0.89
Infantile factors
Gestational age
Full-term (≥39 weeks)	1 (Reference)
Early-term (37–38 weeks)	1.28	1.12–1.47	<0.001
Preterm (35–36 weeks)	1.46	1.01–2.11	0.04
Birth weight
Low (2000–2499 g)	0.49	0.35–0.67	<0.001
Normal (2500–3999 g)	1 (Reference)
Heavy (≥4000 g)	4.26	2.73–6.66	<0.001
Female	1.70	1.49–1.93	<0.001
Past medical history of allergic diseases	1.04	0.86–1.25	0.72

Defined as Supplementary Table S1.

aOR, adjusted odds ratio.

Subgroup Analysis within Neither-Mother Group

Among the 1425 infants in the neither-mother group, the majority attended child care nursery or were cared for by their grandparents. Of those 1425 infants, 489 (34%) were in the both-relative group, 510 (36%) in the either-relative group, and 426 (30%) in the neither-relative group. The background characteristics of the three groups are described in Supplementary Table S5. The incidence proportion of being overweight was 4.1% in the both-relative group, 5.3% in the either-relative group, and 8.2% in the neither-relative group; those differences were significant in the bivariate analysis. However, the adjusted odds ratios for children becoming overweight did not differ whether care was undertaken by relatives or nonrelatives (Table 3).

Table 3.

Factors Associated with Children Being Overweight at Age 3 Years among the Neither-Mother Group

	aOR	95% Confidence interval	p
Environmental factors
Relative child care
Both at 4 and 18 months	1 (Reference)
Either at 4 or 18 months	0.85	0.40–1.78	0.66
Neither at 4 nor 18 months	1.71	0.82–3.55	0.15
Support from partner	0.85	0.40–1.79	0.67
Support from parents	1.56	0.77–3.17	0.22
Support from step-parents	0.83	0.47–1.46	0.52
Smoking family members	0.95	0.55–1.64	0.84
Older siblings	0.82	0.47–1.42	0.47
Sleep duration^a
Short	1.45	0.82–2.57	0.20
Middle	1 (Reference)
Long	0.91	0.34–2.47	0.86
Irregular	1.41	0.33–5.94	0.64
Breastfeeding until 9 months	0.99	0.58–1.70	0.97
Introduction of solid foods
Early (≤4 months)	0.41	0.09–1.83	0.24
Middle (5–6 months)	1 (Reference)
Late (≥7 months)	1.21	0.51–2.85	0.67
Regular mealtime	0.61	0.21–1.72	0.35
Use of precooked foods	0.60	0.35–1.03	0.06
Consumption of cow's milk	0.72	0.38–1.36	0.31
Consumption of sugar-sweetened beverages	1.51	0.87–2.62	0.14
Consumption of sweets or snacks
Never	0.00	0.00–	0.98
Regular	1 (Reference)
Irregular	0.53	0.23–1.23	0.14
Maternal factors
Maternal age at delivery (years)	0.99	0.93–1.04	0.60
Maternal smoking during pregnancy	1.73	0.68–4.42	0.25
Maternal alcohol consumption during pregnancy	1.29	0.66–2.52	0.46
Pregnancy-induced hypertension	1.54	0.31–7.68	0.60
Infantile factors
Gestational age
Full-term (≥39 weeks)	1 (Reference)
Early-term (37–38 weeks)	0.80	0.44–1.47	0.47
Preterm (35–36 weeks)	0.54	0.06–4.59	0.57
Birth weight
Low (2000–2499 g)	0.38	0.08–1.74	0.21
Normal (2500–3999 g)	1 (Reference)
Heavy (≥4000 g)	1.51	0.29–7.81	0.63
Female	1.98	1.14–3.42	0.01
Past medical history of allergic diseases	1.15	0.55–2.43	0.71

Defined as Supplementary Table S1.

Discussion

The overall incidence proportion of children who were overweight was 4.2%. That figure is lower than the incidence proportions previously reported for preschool-aged children in Japan (8.4%¹⁵–13.1%²⁵). The discrepancy in the prevalence of children who are overweight may be the result of differences in the study populations. The study population in the present study was restricted: our sample contained only 3-year-old children who did not require any medical follow-ups; they were less likely to be overweight.

The main purpose of this study was to explore the risk factors associated with becoming overweight in early childhood. Our results indicated that children whose mothers cared for them during the day were less likely to be overweight in early childhood, even after adjusting for children's lifestyles. We also found a dose-dependent relationship between time spent in maternal care and becoming overweight in childhood. Specifically, children without maternal care at ages 4 and 18 months had a 1.5-fold higher risk of being overweight at age 3 years than those who were in maternal care at ages 4 and 18 months.

Mothers continue to play an important role in domestic routines in Japan.²⁶ Maternal employment may be the primary reason for nonmaternal day care; it may have an influence on the type of child care infants experience. Several studies have reported that maternal employment increases the risk of becoming overweight in early childhood. For example, with UK cohort data, Hawkins et al.¹⁷ showed that children had higher risk of being overweight at age 3 years if their mother had worked since their birth. Furthermore, the greater number of hours mothers worked, the higher was the risk that children would be overweight. Phipps et al.¹⁸ observed that in Canada, the mother's history of paid work was associated with a higher probability of their children being overweight. Studies from the United States^19,20 also found an association between maternal employment and children being overweight. The results of the present study are consistent with those previous reports.

Investigations have determined that maternal employment is associated with an increased likelihood of irregular mealtimes and snacking time,¹⁵ more screen-based activities,¹⁶ and decreased sleep duration.¹⁶ The current study directly captured the exposure—outcome relationship by examining the type of child care that likely mediates the association between maternal employment and childhood overweight. According to our results, more attention should be paid to children who are in nonmaternal day care. Healthcare interventions for preventing childhood obesity (including education programs focused on physical activity and eating habits) should target this high-risk population.^27–30

The subgroup analysis of children in nonmaternal day care at age 4 and 18 months yielded no differences in being overweight between those who were cared for by relatives (grandparents, fathers) and those cared for by nonrelatives (child care nursery). Previous studies have reported an increased risk of becoming overweight among children who attended child care nursery compared with those cared for by their parents.^31–35 However, after adjusting for maternal employment, Watanabe et al.¹⁵ observed that care by grandparents (which account for the largest amount of relative care in Japan) influenced childhood overweight.

Center-based child care and relative care are related to a higher risk of childhood overweight than maternal care; however, few studies have directly compared them. Geoffroy et al.³¹ found that children in center-based child care and those cared for by relatives had similar odds ratios for childhood overweight to those in parental care: odds ratios (95% CIs) of 1.65 (1.13–2.41) and 1.50 (0.95–2.38), respectively. Benjamin et al.⁷ reported Z-scores of BMI at 3 years that were not different between children who were cared for by a child care center and those cared for by a nonparent at their own home. These results support our findings, which suggest no obvious differences between relative day care and nonrelative day care.

We also found that children who slept for a long time had lower risk of childhood overweight. This result is consistent with those of various studies, indicating the association between short sleep duration and increased risk of children becoming overweight.^11,16,36,37 The association between lack of sleep and overweight may arise from decreased physical activity through tiredness, metabolic hormonal changes, or additional waking time (which provides increased opportunities to eat).³⁶ Caregivers have a great influence on children's lifestyle, including sleep time. Our results suggest that among child lifestyle variables, sleeping habits were the most influential factor in children becoming overweight. Depending on socioeconomic status, maternal employment and subsequent nonmaternal child care are often inevitable. However, children's sleeping habits may be modified and warrant attention.

The participants in the present study derived from a large population-based sample, with standardized measurements obtained by well-trained public health nurses. However, there are several limitations. First, the data related to several potential confounding variables, such as parental employment, parental adiposity, and socioeconomic status, were unavailable and not included in the analyses. Low socioeconomic status is associated with increased risk for childhood obesity in Japan and Western countries.³⁸ However, from a theoretical perspective, socioeconomic status is related to obesity through dietary or exercise habits,³⁸ which were partially considered in our investigation. Previous studies have also found that paternal work patterns are less influential on the risk of children becoming overweight.^17,18 The results of the present study can still be considered robust despite the lack of information about fathers.

The second limitation was categorization of child care patterns. We only assessed the type of child care at particular ages, not continuously. We also did not assess how much time mothers spent with their children in a day. Therefore, some misclassification of the exposure categories could have occurred. We combined child care nursery and babysitters into nonrelative care; however, previous studies have differentiated between them. Importantly, babysitters are unpopular in Japan (<1% of children are cared for in that way); therefore, the effect of categorizing babysitters was likely negligible.

Third, most of our data were based on parental reports; thus, reporting bias may have occurred. Regarding sleep duration, potential overlap between the categories may also have caused the misclassification. Fourth, since this was an observational study, there may have been unknown or unmeasured confounding variables, or modifying the risk factors may not necessarily improve the outcome. Indeed, for many mothers, their employment might be unavoidable, even if it might increase the risk of childhood obesity. Further studies (e.g., focusing on sleep duration among children with nonmaternal day care) are needed to investigate how they can decrease possible risks among children whose mothers cannot leave their job.

Conclusion

Among environmental factors, less maternal day care and shorter sleep duration were associated with increased risk of becoming overweight during early childhood. Further studies are needed to investigate how the effect of those factors may be diminished with respect to childhood overweight.

Footnotes

Acknowledgment

We thank the Edanz Group () for editing a draft of this article.

Author Disclosure Statement

No competing financial interests exist.

References

Ogden

, Carroll

, Curtin

, et al. Prevalence of overweight and obesity in the United States, 1999–2004. JAMA, 2006; 295:1549–1555.

Stamatakis

, Primatesta

, Chinn

, et al. Overweight and obesity trends from 1974 to 2003 in English children: What is the role of socioeconomic factors?. Arch Dis Child, 2005; 90:999–1004.

Seidell

, Halberstadt

. The global burden of obesity and the challenges of prevention. Ann Nutr Metab, 2015; 66 Suppl 2:7–12.

, Fleming

, Robinson

, et al. Global, regional, and national prevalence of overweight and obesity in children and adults during 1980–2013: A systematic analysis for the Global Burden of Disease Study 2013. Lancet, 2014; 384:766–781.

Ministry of Education C, Sports, Science and Technology. Annual report of School Health Statistics Research. Available at www.mext.go.jp/b_menu/toukei/chousa05/hoken/1268826.htm Last accessed May 31, 2016.

Nader

, O'Brien

, Houts

, et al. Identifying risk for obesity in early childhood. Pediatrics, 2006; 118:e594–e601.

Benjamin

, Sheryl

, Rifas-Shiman

, et al. Early child care and adiposity at ages 1 and 3 years. Pediatrics, 2009; 124:555–562.

Reilly

, Armstrong

, Dorosty

, et al. Early life risk factors for obesity in childhood: Cohort study. BMJ, 2005; 330:1357.

Robinson

, Crozier

, Harvey

, et al. Modifiable early-life risk factors for childhood adiposity and overweight: An analysis of their combined impact and potential for prevention. Am J Clin Nutr, 2015; 101:368–375.

10.

Mazarello Paes

, Ong

, Lakshman

. Factors influencing obesogenic dietary intake in young children (0–6 years): Systematic review of qualitative evidence. BMJ Open, 2015; 5:e007396.

11.

Sekine

, Yamagami

, Handa

, et al. A dose-response relationship between short sleeping hours and childhood obesity: Results of the Toyama birth cohort study. Child Care Health Dev, 2002; 28:163–170.

12.

Ludwig

, Peterspm

, Grortmaker

. Relation between consumption of sugar-sweetened drinks and childhood obesity: A prospective, observational analysis. Lancet, 2001; 357:505–508.

13.

US Bureau of Labor Statistics.. Women in the labor force: A databook. 2015 Available at www.bls.gov/opub/reports/womens-databook/archive/women-in-the-labor-force-a-databook-2015.pdf (last accessed October 17, 2017).

14.

Statistics Bureau, Ministry of Internal Affairs and Communications. Employment status survey. 2012. Available at www.stat.go.jp/data/shugyou/2012/pdf/kgaiyou.pdf (last accessed October 17, 2017).

15.

Watanabe

, Lee

, Kawakubo

. Associations of maternal employment and three-generation families with pre-school children's overweight and obesity in Japan. Int J Obes (Lond), 2011; 35:945–952.

16.

Taylor

, Winefield

, Kettler

, et al. A population study of 5 to 15 year olds: Full time maternal employment not associated with high BMI. The importance of screen-based activity, reading for pleasure and sleep duration in children's BMI. Matern Child Health J, 2012; 16:587–599.

17.

Hawkins

, Cole

, Law

, Group

TMCSCH

. Maternal employment and early childhood overweight: Findings from the UK Millennium Cohort Study. Int J Obes (Lond), 2008; 32:30–38.

18.

Phipps

, Lethbridge

, Burton

. Long-run consequences of parental paid work hours for child overweight status in Canada. Soc Sci Med, 2006; 62:977–986.

19.

Anderson

, Butcher

, Levine

. Maternal employment and overweight children. J Health Econ, 2003; 22:477–504.

20.

Liu

, Hsiao

, Matsumoto

, Chou

. Maternal full-time employment and overweight children: Parametric, semi-parametric, and non-parametric assessment. J Econom, 2009; 152:61–69.

21.

Vital statistics in Kobe. Available at www.city.kobe.lg.jp/information/data/statistics/toukei/jinkou/jinkouugoki.html (last accessed May 31, 2016).

22.

Cole

, Bellizzi

, Flegal

, Dietz

. Establishing a standard definition for child overweight and obesity worldwide: International survey. BMJ, 2000; 320:1–6.

23.

R Core Team; R Foundation for Statistical Computing. 2014. Available at www.r-project.org (last accessed November 1, 2014).

24.

The WHO Child Growth Standards. Available at www.who.int/childgrowth/standards/bmi_for_age/en (last accessed December 28, 2017).

25.

Kato

, Kubota

, Yasui

, et al. Retrospective tracking of young obese children back to birth in Japan: Special attention to the relationship with parental obesity. Asia Pac J Clin Nutr, 2014; 23:641–650.

26.

Organisation for Economic Co-operation and Development.. Gender equality. Balancing paid work, unpaid work and leisure. Available at www.oecd.org/gender/data/balancingpaidworkunpaidworkandleisure.htm (last accessed June 22, 2016).

27.

Kaufman-Shriqui

, Fraser

, Friger

, et al. Effect of a school-based intervention on nutritional knowledge and habits of low-socioeconomic school children in Israel: A cluster-randomized controlled trial. Nutrients, 2016; 8:1–16.

28.

Wen

, Baur

, Simpson

, et al. Effectiveness of home based early intervention on children's BMI at age 2: Randomised controlled trial. BMJ, 2012; 344:e3732.

29.

Redsell

, Atkinson

, Nathan

, et al. Preventing childhood obesity during infancy in UK primary care: A mixed-methods study of HCPs' knowledge, beliefs and practice. BMC Fam Pract, 2011; 12:54.

30.

Sacher

, Kolotourou

, Chadwick

, et al. Randomized controlled trial of the MEND program: A family-based community intervention for childhood obesity. Obesity (Silver Spring), 2010; 18:S62–S68.

31.

Geoffroy

, Power

, Touchette

, et al. Childcare and overweight or obesity over 10 years of follow-up. J Pediatr, 2013; 162:753.e1–758.e1.

32.

Gubbels

, Kremers

SPJ

, Stafleu

, et al. Child-care use and the association with body mass index and overweight in children from 7 months to 2 years of age. Int J Obes (Lond), 2010; 34:1480–1486.

33.

McGrady

, Mitchell

, Theodore

, et al. Preschool participation and BMI at kindergarten entry: The case for early behavioral intervention. J Obes, 2010; 360407.

34.

Maher

, Li

, Carter

, Johnson

. Preschool child care participation and obesity at the start of kindergarten. Pediatrics, 2008; 122:322–330.

35.

Neelon

SEB

, Andersen

, Morgen

, et al. Early child care and obesity at 12 months of age in the Danish National Birth Cohort. Int J Obes (Lond), 2015; 39:33–38.

36.

Taheri

. The link between short sleep duration and obesity: We should recommend more sleep to prevent obesity. Arch Dis Child, 2006; 91:881–884.

37.

Cappuccio

, Taggart

, Kandala

N-B

, et al. Meta-analysis of short sleep duration and obesity in children and adults. Sleep, 2008; 31:619–626.

38.

Kachi

, Otsuka

, Kawada

. Socioeconomic status and overweight: A population-based cross-sectional study of Japanese children and adolescents. J Epidemiol, 2015; 25:463–469.

Supplementary Material

Please find the following supplemental material available below.

For Open Access articles published under a Creative Commons License, all supplemental material carries the same license as the article it is associated with.

For non-Open Access articles published, all supplemental material carries a non-exclusive license, and permission requests for re-use of supplemental material or any part of supplemental material shall be sent directly to the copyright owner as specified in the copyright notice associated with the article.

0.00 MB

0.28 MB