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Case Study On Childhood Obesity

Background

A growing body of evidence suggests that childhood overweight may have its roots in early life. This study aimed to explore patterns of weight in children from birth to 40 months, born between 1994 and 2006, in Halton, Northwest England.

Methods

Halton infants were compared with the UK-90 reference population at four time points (birth, 2 months, 8 months and 40 months) by converting heights and weights into age–sex adjusted SD scores. The mean and SD of Halton SD scores were calculated for each time point and sex. Cohort trends and gender differences in rates of children above the 85th and 95th centiles at each time point were tested for using Poisson regression modelling.

Results

A total of 16 381 births were analysed. At birth, 8 months and 40 months, proportions of Halton children above the 85th and 95th centiles were consistently higher than reference data. Proportions above the 85th and 95th centiles at birth did not change significantly year on year, but for all other time points the proportions increased with subsequent cohorts.

Conclusions

This study may provide evidence that the development of overweight and obesity has its roots in very early life and has highlighted patterns of infant overweight and obesity not previously reported.

children, obesity, public health

Introduction

The prevalence of overweight and obesity has increased in adult and child populations throughout the world during the last two to three decades: obesity prevention has become an international public health priority.1–3 Although there is no consensus over a definition of overweight or obesity in children4–6 and measurement inconsistencies make it difficult to produce an overview of the prevalence of obesity in this group, there is evidence to suggest that childhood obesity is now common in the UK as in other developed countries.7–9 Various factors and influences have been suggested as drivers of the increase in overweight and obesity in children, including: changes in the consumption of fast foods and foods prepared away from home; increases in sedentary pursuits; reductions in walking and cycling; concerns about safety in public places and roads; increases in the availability and marketing of foods; reductions in physical activity at school; and changes in the demands on parents' time.10 However, there is a growing body of evidence to suggest that the development of overweight and obesity in children has its roots in very early life, before many of these factors exert their influence.

Weight in children under school age and in infants has not been as extensively studied as in school age children. This paper contributes to the evidence base by reporting findings from a study that aimed to explore patterns of weight and overweight in children from birth to 40 months, born between 1994 and 2006, in Halton, Northwest England. The objectives of the paper are to describe the Halton data set and to establish how the birthweights, 2-month weights, 8-month weights and 40-month weights/BMIs of successive birth cohorts compare to 1990 reference data (UK90), what this reveals in terms of overweight and obesity, and whether there are any differences according to sex.

Participants and methods

Halton is an area of Northwest England. It has two major towns, Runcorn and Widnes, situated one either side of the River Mersey. The borough was ranked as the 27th most deprived local authority in England out of a total of 326 in 201011 and was in a similar position throughout the period of time that weight data for infants were collected (1994–2006). Employment levels were below the national average. In 2012–13, 11.8% of children aged 4–5 years were classified as obese, higher than the England average of 9.3%.12

Birthweight, weight and length/height at 2, 8 and 40 months of age were recorded on the Child Health System maintained at Western Cheshire Primary Care Trust (PCT) for all births in Halton, since 1994. Birthweight data were obtained from birth notifications; subsequent measurements were carried out by health visitors during routine health surveillance and returned to the Child Health System manager for entry onto the database. Permission to access the database was gained from the Faculty of Applied and Health Sciences Research Ethics Committee, University of Chester, the Halton and St Helens PCT Research and Effectiveness Group and the Records, Data Protection and Information Governance Manager at Halton and St Helens PCT.

Data were available from 1 January 1994 until 31 December 2006: during this time 18 939 live births were recorded in Halton. Excluded from this analysis were multiple births, as these infants tend to have lower birthweights:

  • 477 births that were recorded as twin births;

  • 21 births that were recorded as triplet births;

  • 2060 births that had no record of whether they were singleton or multiple births.

Therefore, a total of 16 381 singleton births recorded on the database were available for inclusion, representing 13 cohorts (birth-years) of children.

As infants and children were not all measured when they were aged exactly 2, 8 or 40 months of age, a range of ages to be included in each age category were used: ‘2 months’ included infants aged from 2 to 3 months; ‘8 months’ included those aged 4 to 12 months and ‘40 months’ included those aged 30 to 54 months. This was in line with comparable epidemiological studies (for example, Bundred et al.4).

For infants or children at birth, 2 and 8 months of age, weight measures were used in this analysis. For children at 40 months of age, body mass index (BMI) was calculated. There is widespread agreement on the use of the BMI to detect overweight and obesity in adults.13 In children, however, the BMI is not a static measurement, varying from birth until adulthood and between girls and boys. Nevertheless, there is widespread international support for using BMI to define overweight and obesity in children once they have reached the age of 40 months.13 Therefore, for this age group, BMI was calculated using the formula weight (kg)/height (m)2. The height, weight and BMI for each child were standardized for age and sex with the British growth reference charts14,15 by conversion to SD scores (standard deviation or z-scores) using the conversion programme obtained from the Child Growth Foundation.16 An SD score of 0 corresponds to the 50th centile of the reference population (RP), an SD score >1.04 indicates that a child is above the 85th centile of the RP and >1.64 means that they are above the 95th centile of the RP. If a population is similar to the RP, we would expect 15% of children to be above the 85th centile and 5% to be above the 95th centile. A BMI >85th centile is defined as overweight and >95th centile as obese.17 SD scores larger than 5 or smaller than −5 were excluded from the analysis as it was presumed that the data were likely to be erroneous.

Mean and standard deviation of SD scores were calculated for each age range and sex. The numbers of children in the sample at each age range above the 85th and 95th centiles were modelled separately as rates using Poisson regression, fitting cohort (year of birth) and sex as covariates.

Results

Table 1 summarizes the whole data set for males and females, respectively. If Halton infants were similar to the UK-90 reference population, the mean weight SD score at any age and either sex would be 0, and the standard deviation of these scores would be 1. Table 1 illustrates that, with the exception of females at 2 months, all mean weight SD scores were >0, indicating that Halton infants were heavier than the reference population (all means statistically different from 0, at least at the 5% level). By 40 months of age, both male and female Halton children were, on average, a quarter standard deviation heavier than UK-90. In addition, the standard deviations for SD scores were all larger than 1 (with the exception of males at birth), showing that Halton infants were more varied than the UK-90 reference population (all SDs statistically different from 1, at least at the 5% level).

Table 1

Sample sizes and summary statistics for age, weight and SD score, by sex

Target measurement age
Birth2 months8 months40 months
Females (n = 7935) 
n (%) 7675 (96.7) 6136 (77.3) 5061 (63.8) 2609 (32.9) 
 Age (months) Mean (SD) −0.12a (0.34) 1.75 (0.33) 8.85 (0.83) 42.5 (2.75) 
5th, 95th centiles −0.7, 0.2 1.3, 2.3 7.8, 10.5 39.0, 47.2 
Min, Max −1.8, 0.46 1.0, 3 6, 12 30.1, 54.0 
 Weight (kg) Mean (SD) 3.33 (0.56) 4.89 (0.65) 8.78 (1.06) 16.02 (2.32) 
 SD score Mean (SD) 0.19 (1.02) −0.05 (1.03) 0.13 (1.12) 0.25 (1.14)b
  >85th centile % (n19.2 (1476) 13 (797) 20.1 (1017) 22.6 (589)b
  >95th centile % (n7.5 (573) 4.2 (259) 9 (453) 9.3 (242)b
Males (n = 8393) 
n (%) 8113 (96.7) 6352 (75.7) 5301 (63.2) 2774 (33.1) 
 Age (months) Mean (SD) −0.13a (0.36) 1.76 (0.34) 8.88 (0.84) 42.5 (2.69) 
5th, 95th centiles −0.7, 0.5 1.3, 2.4 7.8, 10.6 39.1, 47.0 
Min, Max −12.3, 0.9 1.0, 3 7.3, 12 30.4, 54.0 
 Weight (kg) Mean (SD) 3.45 (0.59) 5.34 (0.74) 9.44 (1.09) 16.45 (2.17) 
 SD score Mean (SD) 0.15 (1.00) 0.08 (1.05) 0.16 (1.07) 0.25 (1.12)b
  >85th centile % (n17.9 (1456) 16.2 (1029) 19.6 (1041) 21.9 (607)b
  >95th centile % (n7 (566) 5.7 (359) 8.5 (448) 9.1 (252)b
Target measurement age
Birth2 months8 months40 months
Females (n = 7935) 
n (%) 7675 (96.7) 6136 (77.3) 5061 (63.8) 2609 (32.9) 
 Age (months) Mean (SD) −0.12a (0.34) 1.75 (0.33) 8.85 (0.83) 42.5 (2.75) 
5th, 95th centiles −0.7, 0.2 1.3, 2.3 7.8, 10.5 39.0, 47.2 
Min, Max −1.8, 0.46 1.0, 3 6, 12 30.1, 54.0 
 Weight (kg) Mean (SD) 3.33 (0.56) 4.89 (0.65) 8.78 (1.06) 16.02 (2.32) 
 SD score Mean (SD) 0.19 (1.02) −0.05 (1.03) 0.13 (1.12) 0.25 (1.14)b
  >85th centile % (n19.2 (1476) 13 (797) 20.1 (1017) 22.6 (589)b
  >95th centile % (n7.5 (573) 4.2 (259) 9 (453) 9.3 (242)b
Males (n = 8393) 
n (%) 8113 (96.7) 6352 (75.7) 5301 (63.2) 2774 (33.1) 
 Age (months) Mean (SD) −0.13a (0.36) 1.76 (0.34) 8.88 (0.84) 42.5 (2.69) 
5th, 95th centiles −0.7, 0.5 1.3, 2.4 7.8, 10.6 39.1, 47.0 
Min, Max −12.3, 0.9 1.0, 3 7.3, 12 30.4, 54.0 
 Weight (kg) Mean (SD) 3.45 (0.59) 5.34 (0.74) 9.44 (1.09) 16.45 (2.17) 
 SD score Mean (SD) 0.15 (1.00) 0.08 (1.05) 0.16 (1.07) 0.25 (1.12)b
  >85th centile % (n17.9 (1456) 16.2 (1029) 19.6 (1041) 21.9 (607)b
  >95th centile % (n7 (566) 5.7 (359) 8.5 (448) 9.1 (252)b

Figures 1 and 2 show details of the weights/BMIs of infants in each of the year cohorts, for females and males, respectively. The proportion of infants with birthweights, 8-month weights and 40-month BMIs above the 85th and 95th centiles was fairly consistently above the expected 15 and 5%, respectively, in comparison to the UK-90 data. At 2 months of age, the proportions of infants above the 85th and 95th centiles were generally much nearer the 15 and 5% that would be expected and had fallen in comparison to birthweight scores.

The results from the Poisson regression modelling of rates of children classified above the 85th and 95th centiles, as compared with the UK-90 reference data, fitting cohort and sex as covariates, are displayed in Table 2. Incidence rate ratios (IRRs) and 95% CIs are presented. In terms of a cohort effect, the IRRs give the average rate ratio for 1 year. So, for example, at 40 months, the proportion of children above the 85th centile increased by a factor of 1.033, or 3.3%, per year during the study period. There is a statistically significant cohort effect for both males and females at every measurement target except birth, that is to say the weight/BMI of infants aged 2, 8 and 40 months was heavier year on year (see Figs 1 and 2).

Table 2

Poisson regression modelling of rates of children classified above 85th centile and above 95th centile compared with UK-90 reference fitting cohorta and gender as covariates: incidence rate ratios (95% CI)

BirthP2 monthsP8 monthsP40 monthsbP
>85th centile 
 Cohort effectc1.00 (0.99–1.01) 0.42 1.025 (1.01–1.04) <0.001 1.015 (1.00–1.03) 0.021 1.033 (1.01–1.06) 0.005 
 Gender effectd0.930 (0.865–1.00) 0.0497 1.242 (1.13–1.36) <0.001 0.978 (0.90–1.07) 0.62 0.97 (0.87–1.09) 0.59 
>95th centile 
 Cohort effectc1.00 (0.99–1.02) 0.65 1.031 (1.01–1.05) 0.008 1.023 (1.00–1.04) 0.016 1.038 (1.00–1.08) 0.039 
 Gender effectd0.94 (0.83–1.05) 0.27 1.32 (1.13–1.55) <0.001 0.94 (0.83–1.08) 0.36 0.98 (0.82–1.17) 0.82 
BirthP2 monthsP8 monthsP40 monthsbP
>85th centile 
 Cohort effectc1.00 (0.99–1.01) 0.42 1.025 (1.01–1.04) <0.001 1.015 (1.00–1.03) 0.021 1.033 (1.01–1.06) 0.005 
 Gender effectd0.930 (0.865–1.00) 0.0497 1.242 (1.13–1.36) <0.001 0.978 (0.90–1.07) 0.62 0.97 (0.87–1.09) 0.59 
>95th centile 
 Cohort effectc1.00 (0.99–1.02) 0.65 1.031 (1.01–1.05) 0.008 1.023 (1.00–1.04) 0.016 1.038 (1.00–1.08) 0.039 
 Gender effectd0.94 (0.83–1.05) 0.27 1.32 (1.13–1.55) <0.001 0.94 (0.83–1.08) 0.36 0.98 (0.82–1.17) 0.82 

In terms of sex, the IRR is a comparison of males with females. For example, at birth, the proportion of males above the 85th centile was on average 0.930 times (or 7% lower than) that for females. There were only three trends where a statistically significant sex effect was observed. At birth, this is close to being non-significant so is a cautionary finding. At 2 months, the sex effect is marked at both thresholds, above the 85th and above the 95th centiles, indicating that males were on average 1.24 times more likely to be above the 85th centile for weight and 1.32 times more likely to be above the 95th centile.

Discussion

Main findings of this study

Analysis of the whole data set revealed that the study population was heavier and more varied than the UK-90 reference population. Birthweight remained relatively stable, but with the percentage of males and females with a birthweight above the 85th and 95th centiles consistently above 15 and 5% that would be expected in comparison with the 1990 reference data throughout the 13-year period, it is apparent that heavier birthweights are an entrenched position. At 2 months, the proportion of infants above the 85th and 95th centiles had fallen in comparison to birthweights, but was increasing in successive birth cohorts in both males and females. Subsequently, at 8 and 40 months, the proportion of infants above the 85th and 95th centiles for weight/BMI was much higher than expected in comparison to the UK90 reference data and was increasing over time in males and females. Therefore, these data show that Halton children had a higher prevalence of overweight and obesity than the UK-90 reference population at all target age ranges except 2 months, and that incidence has been increasing year on year with successive cohorts at all target ages except birth.

What is already known on this topic?

There is some evidence of the development of overweight in pre-school children in the UK. A cohort study of 1031 children born in the Bristol Avon area in 1991–92 demonstrated an excess of overweight and obesity before the age of school entry.18 Stenhouse et al.19 reported on a sample of 4665 Plymouth infants aged 24–30 months in 1996–97, who had a higher BMI standard deviation score than the UK-90 reference population, indicating the development of overweight. Similarly, Bundred et al.4 studied 35 662 Wirral infants and 28 768 Wirral children over the decade to 1998. They identified significantly higher proportions than would be expected of overweight and obese children aged 2.9–4 years of age in a population-based series of cross-sectional studies between 1989 and 1998, also using the UK-90 reference data as standard and the 85th and 95th centiles as cut-off points. Furthermore, the proportions were increasing over the 10-year period studied. They concluded that as the increase in the proportion of children above the 85th and 95th centiles for weight was not present in infants, the excessive weight gain occurred between infancy and pre-school,4 that is between the ages of 3 months and 4 years. This conclusion was subsequently supported by the work of Gardner et al.20 who reported that in a cohort of 233 British children measured at birth, 5 years and 9 years, most excess weight was gained by 5 years of age.

What this study adds

In this study, routinely collected data were utilized to explore patterns of overweight in Halton infants and children. The main strength of the work lies in the size of the data set: 16 381 singleton births comprising 13 birth cohorts. Inevitably, weight was not recorded for each individual at every data collection point, but the proportion of measurements available was high: at birth nearly 100%; at 2 and 8 months, data were available for more than two-thirds of births for the majority of year cohorts; and at 40 months around 50% of each birth cohort had a measurement recorded. Thus, patterns in the data are likely to reflect the totality of singleton births in Halton.

As outlined above, there is some research evidence pointing to the development of overweight in pre-school children. However, in the present study, weights at 8 months of age were presented, and it was evident that by this age there was an excess of individuals above the 85th and 95th centiles, a finding not previously reported. As the increase in the proportion of children above the 85th and 95th centiles for weight was not present in infants aged 2 months, it could be concluded that excessive weight gain occurred, at least for some children, long before the age of 4–5 years as hypothesized in other studies,4,20 instead occurring between 2 and 8 months.

The picture is slightly complicated, however, when birthweights are examined. As demonstrated, at birth, since 1994, there was a consistently higher proportion of infants above the 85th and 95th centiles for weight than would be expected using the 1990 reference data as standard. It appears, therefore, that this excess disappears at 2 months, only to re-establish itself at 8 months. The explanation could be that, at birth, the gestational age of the infant was used in the calculation of the SD score, but at 2 months the actual age of the baby, determined by using birth date and measurement date, was used. Infants born before 40-week gestation and likely to be lighter may not have had time to ‘catch up’ with their weight, and hence, this may have lowered the proportions above the thresholds. If this is the case, the hypothesis that the development of overweight can have its roots in very early life is strengthened, as many infants subsequently gained excess weight between 2 and 8 months.

What factors might influence this early development of overweight? An independent positive association between higher birthweight and obesity in infancy and childhood has been demonstrated in a number of studies21,22 , and an association between early rapid weight gain and an increased risk of obesity in babies with a normal birthweight has also been demonstrated.23 Breastfeeding may convey a lower risk of overweight, through behavioural or nutritional mechanisms or effects on growth.24 It was not possible to know whether the infants in this study had been breast or bottle fed, although breast feeding rates in Halton are generally low, with breastfeeding initiation at ∼47% and infants totally or partially breastfed at 6–8 weeks of age 17%.25 Finally, between the ages of 2 and 8 months, infants will generally be weaned, that is introduced to food other than milk. Despite the magnitude of the change represented by weaning, there has been relatively little research focussed on the weaning period, the nature of foods given, or whether this period of dietary change influences growth and development, or later health and morbidity.26–28

In terms of overweight in children as a public health issue, it is worth highlighting that the proportion of Halton children being measured at 40 months was declining over the years of this study. This probably reflects changes in the organization of health visiting practice and services, but is an issue that warrants further consideration given the evidence indicating that overweight may have its roots early in a child's life. The National Child Measurement Programme has demonstrated that in Halton, by the time children reach reception year at school, 28.9% of males and 24.0% of females are overweight or obese.29 Data presented here indicate that similar proportions are overweight or obese earlier, at 40 months of age, with evidence of the development of overweight already discernable at 8 months. Identifying children with weight problems before they reach school age would enable earlier intervention where necessary.

Limitations of this study

There are a number of limitations to the study that need to be considered, some of which are considerations in all studies utilizing routinely collected data and others specific to this study. First, it is difficult to assess the accuracy with which the weight measurements were taken. Data were collected by health professionals using standard procedures and equipment. However, measurements will have been taken by a number of different individuals and there is no way of checking for inter-observer differences. Data entry was carried out by trained NHS clerical staff, but there is no direct way of checking the accuracy of data entry either. Missing data are often an issue with routinely collected data, and as has been outlined above, in this study measurements were not available for every individual at every measurement point.

In relation to this study specifically, although the data set was large, this was a localized sample that may limit the generalizability of the findings. In addition, the presented cohort effect for age 40 months is limited to 1994–2002 only (1994–2006 for other ages), which means that it is not such a strong finding. We have demonstrated the early development of overweight by 8 months of age, but it is not possible in this analysis to say whether it is the same children who remain overweight at 40 months of age. Finally, there are other data that could have been collected which would have been useful, such as whether mothers breastfed or formula fed, the weight/BMI status of mothers and whether they smoked, but these were not routinely collected, or at least not in a format in which it was possible to amalgamate them with the weight data.

Conclusion

This study has provided further evidence that the development of overweight and obesity may have its roots in very early life and has highlighted patterns of infant overweight and obesity not previously reported at 8 months of age. The exploration of early influences, such as weaning, on the development of eating patterns, and the relationship of this to overweight and obesity, could provide useful information in the attempt to address this very important public health issue.

Acknowledgements

We are very grateful to Dr Peter Bundred for explaining the use of the conversion programme obtained from the Child Growth Foundation and for help with initial data analysis.

References

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The levelling off of the obesity epidemic since the year 1999—a review of evidence and perspectives

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Establishing a standard definition for child overweight and obesity worldwide: international survey

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Through the National Early Care and Education Learning Collaboratives project, the Centers for Disease Control and Prevention (CDC) funded Nemours Children’s Health System to support the spread and scale of best practices related to obesity prevention in early care and education (ECE) settings.

For five years (2011 – 2016), Nemours and CDC worked with grantees in ten states to work directly with thousands of ECE providers on program improvements related to healthy eating, physical activity, breastfeeding and screen time. Grantees also worked at the state level to embed best practices into ECE systems such as professional development, licensing and Quality Rating and Improvement Systems. A series of case studies by state and topic area highlight lessons learned, successes and challenges in using the ECE setting as a lever in the fight against childhood obesity.

Using a Spectrum of Opportunities to Support Childhood Obesity Prevention in Early Care and Education Settings: A Series of Case Studies

Case studies by state:

Arizona

North/Central Florida

South Florida

Indiana

Kansas

Kentucky

Missouri

New Jersey

Virginia

Case studies by topic area:

Child and Adult Care Food Program (CACFP)

Emerging Opportunities

Licensing and Administrative Regulations

Pre-Service and Professional Development

Quality Rating and Improvement Systems

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