The results reported here show that CVD risk in young children is associated with perinatal and infancy factors among NHW. Specifically, our analysis shows that breastfeeding is protective against obesity and smoking during pregnancy is a risk factor for obesity in NHW. Low birth weight was not a risk factor for CVD risk factors, particularly among NHW women. With the exception of breastfeeding being protective against the highest quintile of non-HDL cholesterol in NHB, early introduction of solid foods, smoking during pregnancy, and low birth weight were not found to be related to CVD risk factors in early childhood.
Previous NHANES analyses have shown mixed results when analyzing whether or not breastfeeding is protective against children becoming overweight and that there is a dose-dependent effect based on duration. One analysis of infant feeding and child overweight status among 3-to-5-year olds from the NHANES III showed that after adjusting for potential confounders, there was a reduced risk of being overweight for ever-breastfed children compared with those never breastfed [22
]. However, there was no reduced risk of being overweight (obese). Furthermore, there was no demonstrable threshold effect or clear dose-dependent effect of the duration of full breastfeeding on being at risk of overweight or overweight (now termed overweight and obese).
Other large population-based studies have also examined whether increasing duration of breastfeeding is associated with a lower risk of overweight in a low-income population of 4-year olds in the United States. Analysis from the Pediatric Nutrition Surveillance System [23
] of children up to 60 months of age found that the duration of breastfeeding showed a dose-response, protective relationship with the risk of overweight only among NHW; no significant association was found among NHB or Hispanics, very similar to our results reported here.
Others have examined a broad range of factors that may simultaneously contribute to childhood overweight in a population-based cohort of children followed from birth to 4.5 years, to determine which factors exert the most influence in early life [24
]. The Quebec Longitudinal Study of Child Development 1998–2002 (QLSCD) followed a representative sample (n
= 2103) of children born in 1998 in the Canadian province of Quebec. Measured height and weight were available for 1550 children aged 4.5 years. Results showed that being in the highest quintiles of weight gain between birth and 5 months, as well as maternal smoking during pregnancy, almost doubles the odds of being overweight at 4.5 years.
The Viva La Familia Study was designed to identify genetic and environmental factors affecting obesity and its comorbidities in 1030 Hispanic children from 319 families [25
]. Salient independent risk factors for childhood obesity in this cohort of Hispanic children were age, birth weight, maternal obesity, paternal obesity, number of children in the family, and the percentage of awake time spent in sedentary activity. They also reported that breastfeeding might have a small protective effect against childhood obesity, although the authors concluded that residual confounding might exist. The authors reported no significant effect of early introduction of solid foods on childhood obesity, consistent with our findings here. Conversely, a prospective nationally representative cohort study conducted in England, Wales, Scotland, and Northern Ireland [26
] included 13,188 singleton children aged 3 years in the Millennium Cohort Study, born between 2000 and 2002, who had complete height/weight data. The main outcome measure was childhood overweight (including obesity) defined by the International Obesity Task Force cut-offs for body mass index. In the fully adjusted model, primarily individual- and family-level factors were associated with early childhood overweight: birthweight z-score, black ethnicity (compared with white), introduction to solid foods <4 months, and smoking during pregnancy. However, in agreement with both the findings here and in the Viva La Familia Study, breastfeeding ≥4 months (compared with none) was associated with a decreased risk of early childhood overweight.
Other population-based studies have shown an association between maternal smoking during pregnancy and childhood obesity. Specifically, a total of 11,653 preschool children participating in the UK Millennium Cohort Study had their weight gain z-scores calculated from 3 to 5 years [27
]. In a mutually adjusted model, children were more likely to gain weight rapidly if their mothers smoked during pregnancy. Due to the cross-sectional nature of the current dataset, we were unable to explore longitudinal growth but the concept of catch-up growth has gained recent and increased attention in the literature [28
Because our findings are among very young children, they may have implications throughout childhood. Our group has reported previously that risk factors for cardiometabolic disease can be detected as early as the preschool years (12) and 8 years old [31
]. Other studies have noted that several CVD risk factors persist strongly and consistently through childhood into adulthood [32
]. The Cardiovascular Risk in Young Finns Study was one of the first groups to explore childhood predictors of the metabolic syndrome (MS), a constellation of abnormal waist circumference, insulin resistance, dyslipidemia, and hypertension [32
]. In this study, fasting insulin at baseline was related to development of the syndrome after a 6-year follow-up of 1,865 children and adolescents 6-to-18-years-old. Reported results showed that baseline insulin concentration was higher in children who subsequently developed the MS, lending support to the theory that insulin resistance precedes the development of the condition in childhood.