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Journal of Public Health Advance Access originally published online on March 3, 2008
Journal of Public Health 2008 30(2):139-144; doi:10.1093/pubmed/fdn013
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© The Author 2008, Published by Oxford University Press on behalf of Faculty of Public Health. All rights reserved

Trends in overweight and obesity among 5–7-year-old White and South Asian children born between 1991 and 1999



Ravikumar Balakrishnan, Specialist Registrar1

Premila Webster, Hon. Senior Lecturer1

Don Sinclair, Director of Public Health2
1 Department of Public Health, University of Oxford, Old Road, Headington, Oxford OX3 7LF, UK
2 Berkshire East Primary Care Trust, Beech House, Upton Hospital, Albert Street, Slough SL1 2BJ, UK

Address correspondence to Premila Webster, E-mail: premila.webster{at}dphpc.ox.ac.uk

Objective To determine the trends in overweight and obesity among White and South Asian children aged 5–7 years born between 1991 and 1999 and included in the East Berkshire Child Health System.

Methods Children were grouped into nine cohorts based on their year of birth. The UK National BMI percentile classification was used to classify the children as overweight and obese and to examine the prevalence and trends by year of birth, sex and ethnicity.

Results Overall, more boys (10.1%; 9.7–10.6%) than girls (9.1%; 8.7–9.6%) were obese (P < 0.003). South Asian boys were more likely to be overweight (OR 1.92; 95% CI 1.62–2.28; P < 0.01) and obese (OR 1.53; 95% CI 1.28–1.89; P < 0.01) than South Asian girls. Overweight (1.77; 1.56–2.00; P < 0.05) and obesity (1.76; 1.50–2.06; P < 0.05) were significantly higher among South Asian boys compared with their White counterparts (baseline). After adjusting for sex, ethnicity and year of birth, South Asian children were 27% more overweight (P < 0.01) and 45% more obese (P < 0.01) compared with White children, and boys were 6% more overweight (P = 0.04) and 12% more obese (P = 0.003) compared with girls. There was an increasing trend in overweight among boys (P = 0.01) and girls (P = 0.003); and in obesity among boys (P < 0.001) and girls (P = 0.008) in children born from 1991 to 1999.

Conclusion There is a significant rise in childhood obesity among 5–7-year-old children. Overweight and obesity among South Asian boys are significantly higher than that among South Asian girls. This group may be at greater risk of morbidity and mortality related to obesity and may need to be targeted appropriately for interventions to reduce obesity.

Keywords: childhood obesity, South Asian, trends


   Introduction
TOP
 Introduction
Method
 Statistical analysis
 Results
 Discussion
 References
 
Childhood obesity has reached epidemic levels in developed countries. Between 1984 and 1998, prevalence of overweight between 7–11-year olds in the UK rose from 8 to 20%.1 Between 1995 and 2003, the prevalence of obesity among children aged 2–10 in the UK rose from 9.9 to 13.7%.2 A rise in childhood obesity is of particular concern as childhood and adolescent obesity predisposes to obesity in adulthood.3,4 There appears to be a variation in obesity by ethnic groups. In the United States, a large variation in childhood obesity by ethnic groups was shown.5 Over a 30-year period, the prevalence of overweight increased 3-fold (4–13%) among 6–11-year-old White children, but 5-fold (4–20%) among Black children. In most gender-age groups, Mexican-American children experienced increases in overweight that were between those experienced by Blacks and Whites. Differences between ethnic groups were less marked among 2–5-year olds, and in this age group, White children experienced the largest increase in overweight (from 4 to 9%).6 Between 1999 and 2002, the prevalence of extreme obesity, BMI levels (99th percentile) reached 6–7% among Black girls and Mexican-American boys.6 Ethnic differences in the prevalence of overweight and obesity among children at school entry have been reported in the UK.7–9 However, there were no reports assessing the trend. British South Asian children were reported to have higher cardiovascular risk compared with White children.10 An understanding of the trend and prevalence of obesity and overweight in children in this age group is important to develop effective public health interventions.


   Method
TOP
 Introduction
 Method
Statistical analysis
 Results
 Discussion
 References
 
Participants
There were 51 565 children born between January 1991 to December 1999 in East Berkshire and included in the Child Health Information System. Among them, 29 641 children with height and weight data measured by school nurses in year 1 (5–7 years old) were included in this study.

Measuring obesity in children
Height and weight were measured at school, by school nurses (trained in collecting height and weight) for all children at school entry (year 1) every year. Children's height was measured in centimeters (to the nearest half centimeter) without shoes using stadiometers. Children's weight was measured in kilograms, to the nearest 100 g unit (0.1 kg) with normal indoor clothing without shoes using mechanical scales (calibrated annually).

Children were grouped into nine cohorts based on their year of birth. The UK National BMI percentile classification11 was used to classify the children as overweight and obese, and we examined for trends by year of birth, sex and ethnicity. Actual date of birth was used to calculate the age of the children at the time of measurement of height and weight. BMI was calculated from the height and weight data using the formula BMI = weight (kg)/height (m2).


   Statistical analysis
TOP
 Introduction
 Method
 Statistical analysis
Results
 Discussion
 References
 
STATA (version 10) package was used for statistical analysis. The outcome measures were overweight (>85th percentile) and obesity (>95th percentile) BMI percentile cut-offs of the UK reference data.11 Pearson's {chi}2-test was used to test the statistical significance of differences in proportions. Mantel-Haenszel's {chi}2-test for linear association was used to investigate trends in the prevalence rates over the study period. Prevalence odds ratio (POR) was calculated as obesity is a chronic condition and its risk factors like ethnicity and sex are long-lasting. Multiple logistic regression models for overweight and obesity with sex, ethnicity and birth year as explanatory variables were used. P-values (two-sided) of <0.05 were considered statistically significant.


   Results
TOP
 Introduction
 Method
 Statistical analysis
 Results
Discussion
 References
 
Height and weight data were available for 29 641 (57.5%) of the 51 565 children born between January 1991 and December 1999 in East Berkshire and registered in Child Health Information System. Table 1 shows that the non-responders (i.e. children without height and weight data) did not differ significantly from those who have, either by sex (P = 0.88) or ethnicity (P = 0.40).


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  		Table 1 Demographic characteristics of study population (N = 51 565)a

 
Prevalence of overweight and obesity by sex and ethnicity
Table 2 shows the prevalence of overweight and obesity among 5–7-year-old children born between 1991 and 1999 by sex and ethnicity. Overall, boys were significantly more obese than girls (10.1 versus 9.1%; P < 0.003). Table 3 shows the unadjusted POR for factors affecting prevalence of overweight and obesity by sex and ethnicity. Initially girls were taken as the baseline category and POR was calculated overall and for each ethnic category. South Asian boys were more likely to be overweight (OR 1.92; 95% CI 1.62–2.28; P < 0.01) and obese (OR 1.53; 95% CI 1.28–1.89; P < 0.01) than South Asian girls. There were no significant differences in obesity and overweight between boys and girls either in White or Afro-Caribbean ethnic groups. Then POR was calculated for South Asian and Afro-Caribbean children with White children as the baseline category. Overweight (1.77; 1.56–2.00; P < 0.05) and obesity (1.76; 1.50–2.06; P < 0.05) were significantly higher among South Asian boys compared with those among their White counterparts. However, overweight among South Asian girls (0.86; 0.75–0.99; P < 0.05) was significantly lower than that among their White counterparts. Table 4 shows the adjusted prevalence odds ratio (aPOR) for multiple logistic regression models of factors including sex, ethnicity and year of birth. After adjusting for other factors in the table, overweight and obesity were significantly higher among boys and South Asian children.


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  		Table 2 Prevalence of overweight and obesity among 5–7-year-old children born between 1991 and 1999 by gender and ethnicity

 


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  		Table 3 Unadjusted POR for factors affecting prevalence of overweight and obesity among 5–7-year-old children in East Berkshire by sex and ethnicity

 


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  		Table 4 aPOR for multiple logistic regression model of factors affecting prevalence of overweight and obesity among 5–7-year-old children in East Berkshire

 
Trends in overweight and obesity by sex and ethnicity
Proportion of overweight children increased significantly among boys ({chi}2 linear trend = 6.39, P = 0.01) and girls ({chi}2 linear trend = 8.55, P = 0.003) for those who were born in 1991–99. A similar increase in trend was also shown for obesity in boys ({chi}2 linear trend = 12.77, P < 0.001) and girls ({chi}2 linear trend = 7.02, P = 0.008) (Fig. 1).


Figure 1
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  		Fig. 1 Trends in overweight and obesity (with 95% CI) among 5–7-year-old children by gender and year of birth (1991–1999).

 
Among the 29 641 children, ethnicity details were recorded for 16 364 (55%). The proportion of boys (51.2%, 95% CI 50.6–51.7) and girls (48.8%, 95% CI 48.3–49.4) with ethnicity recorded was similar to the proportion (boys 51.1%, 95% CI 50.4–51.7) and girls (48.9%, 95% CI 48.3–49.6) with ethnicity unrecorded.

Owing to small number of children with ethnicity recorded in 1991, data for that year was omitted in the trend analysis by ethnicity. Overweight and obesity appear to increase over the years in both White and South Asian groups but more steeply in the latter though the trends are not statistically significant (Fig. 2).


Figure 2
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  		Fig. 2 Trends in overweight and obesity (with 95% CI) among 5–7-year-old children by ethnicity and year of birth (1991–1999).

 

   Discussion
TOP
 Introduction
 Method
 Statistical analysis
 Results
 Discussion
References
 
Main finding of this study
The study shows a significant increase in childhood overweight and obesity among 5–7-year olds, with the prevalence being higher in boys than girls. Among South Asian children, boys are almost twice as likely to be overweight and 1.5 times to be obese than girls.

What is already known on this topic
Overweight in children is a serious public health problem in Britain.1,2 The incidence of childhood obesity is increasing and likely to persist into adult life.3,4 Obesity results in considerable morbidity and mortality of which cardiovascular disease is one of the principal causes.12,13 Migrant populations of South Asians living in the West are at a higher risk of cardiovascular disease compared with the White population.14 In the UK, ethnic differences in the prevalence of overweight and obesity among children at school entry has been reported.7–9

What this study adds
There is a significant increase in childhood overweight and obesity among 5–7-year-old born between 1991 and 1999. The prevalence is higher in boys than in girls. The trend increased more steeply in South Asian children, with South Asian boys almost twice as likely to be overweight and 1.5 times to be obese as South Asian girls.

Limitations of this study
Different growth patterns in boys and girls at each age mean that a universal categorization cannot be used to define childhood obesity (as with adults). Each sex and age group therefore needs its own level of classification for obesity. This study uses the UK National BMI percentile classification to describe childhood overweight and obesity.11 This gives the BMI threshold for each age and for boys and girls separately above which a child is considered overweight or obese. There are alternative methods for measuring childhood obesity, specifically an international classification developed by the International Obesity Task Force.15 There is an ongoing debate regarding which classification of childhood obesity is more robust. Using the UK National BMI percentile classification was considered appropriate for this study as it provides a reference point that is derived from information about the UK population and is the method used in the English Health Surveys.11

Although the data were from children registered in East Berkshire Child Health System, the catchment area covers a diverse population ranging from the more deprived area of Slough (deprivation score of 20.87) with a 28% South Asian population to the affluent areas of Windsor and Maidenhead (deprivation score of 8.22), with 4.6% South Asians and Bracknell Forest (deprivation score of 8.61) with 1.9% South Asians.

Although the study shows that the non-responders (i.e. children without height and weight data) did not differ significantly from those who have, either by sex or ethnicity socio-economic data were not collected as the children were measured in primary school and it was not possible to collect this data from the children. In addition, data collected did not include independent schools. Although children who attend state schools tend to be from a range of socio-economic backgrounds, the exclusion of independent schools (which would almost exclusively have children from higher socio-economic backgrounds) means that the impact of socio-economic status on childhood obesity cannot be assessed in this study.

Overweight and obesity in childhood have a significant effect on both physical and psychological health. South Asians living in the west are at a higher risk of cardiovascular disease compared with the White population,14,16–18 and a UK study estimating the prevalence of childhood type 2 diabetes and maturity onset diabetes of the young concluded that South Asian children were at a significantly higher risk.19 Evidence suggests that prevention could be the key for controlling the current epidemic of obesity. Studies have investigated general patterns of dietary change after migration.19,20 Migrants tend to retain staple foods from their own culture longest and introduce new foods selected from the host culture based primarily on taste.19 Research carried out to identify changes in the diet of a South Asian transmigratory population collected data on dietary information on South Asian children aged 9–11 in Bradford.21 The results suggest that novel sweet items were notably introduced to the children's diet in Bradford (e.g. breakfast cereals and fizzy drinks), whereas traditional items (chapatti, curry) persist.21 Research suggests that interventions should focus on identifying at-risk and overweight children at an early stage and educating families about the health consequences of being overweight.22 Young children are a priority group for intervention strategies and it is vital that suitable interventions are targeted at appropriate groups to be effective. South Asian children, especially boys, may be at greater risk of morbidity and mortality related to overweight and so may be a priority for specific initiatives identifying and promoting healthy diets that are appropriate to South Asians, culturally sensitive and target both the children and parents.


   References
TOP
 Introduction
 Method
 Statistical analysis
 Results
 Discussion
 References
 

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