Prevalence of obesity and associated risk factors in chinese pre school children aged 6 to 72 months old in singapore 1

1 PREVALENCE OF OBESITY AND ASSOCIATED RISK FACTORS IN CHINESE PRE-SCHOOL CHILDREN AGED 6 TO 72 MONTHS OLD IN SINGAPORE Although the prevalence of obesity has been steadily increasing w

1

PREVALENCE OF OBESITY AND ASSOCIATED RISK FACTORS IN CHINESE PRE-SCHOOL CHILDREN AGED 6 TO 72 MONTHS OLD IN SINGAPORE

Although the prevalence of obesity has been steadily increasing worldwide for many years, the steep rise in the number of obese children and adolescents since 1980s5, 6 has elevated obesity to epidemic status, putting it at the top of the WHO’s Public Health agenda.7

1.1.1 Aetiology of Obesity

Multiple factors such as genetics8-13 and behavioral factors14-17 may contribute to obesity There are several reports of gene mutations associated with

2

body weight regulation Variations in the fat mass and obesity-associated gene (FTO) show a strong and highly significant correlation with obesity but the mechanisms remains unclear.8-10 Moreover, genome-wide association studies showed that a variation in the PFKP gene involved in glycolysis is also strongly associated with obesity.8 Leptin and leptin receptor genes are two well-known factors that play a role in obesity Polymorphism in either the leptin gene or the leptin receptor gene can produce inactive leptin or inefficient leptin action (leptin receptor dysfunction), and increased neuropeptide Y level, resulting in overweight

or obesity.11-13

In the past three decades, overweight and obesity have become primary problems in Western countries Many other countries have now adopted the Western culture and behavior and have changed their food consumption behavior because of increased availability and accessibility of fast foods and manufactured foods which are high in fat and sugar For recreation, adults spend more time watching television, playing video games, browsing the web and other internet-related activities A sedentary life style combined with physical inactivity and unhealthy foods explain the growing epidemic of obesity for both young and old people.1, 14-17

1.1.2 Consequences of obesity

Obesity can cause weight-related problems and even mortality.1,18Complications of childhood obesity include high blood pressure,19,20 high

3

cholesterol,20 diabetes,21 and in later years, early heart diseases.22,23 Other morbidities associated with childhood obesity are orthopedic problems, skin fungal infections, acanthosis nigracans, hepatic steatosis, pseudotumor cerebri and psycho-social consequences.24-26 Moreover, overweight children are more likely

co-to remain overweight as adults.18,27,28

One of the cardiovascular risk factors of obesity is hyperlipidemia.26 The prominent sign of hyperlipidemia is central fat distribution and the symptoms are elevated serum low-density lipoprotein cholesterol (LDL) and triglycerides (TG) but lowered high-density lipoprotein cholesterol (HDL).20, 25 The mechanism is the same as in adults Obese children possess increased free fatty acids in their blood circulation resulting from lipolysis and hyperinsulinemia due to increased intake of food.25 Free fatty acids stimulate the hepatic synthesis of LDL and TG which can lead to fat deposition and obesity.25 Non-insulin dependent diabetes mellitus is another complication Increased body fat mass cause increased basal insulin secretion and impaired glucose tolerance.25, 29 A possible mechanism for high blood pressure in obese individuals is hyperinsulinemia Activation of the rennin-angiotensin-aldosterone system and reduction of renal sodium excretion by hyperinsulinemia are explanations for high blood pressure in obese individuals.25,

29

Hypertension is also a risk factor for cardiovascular diseases. 26

Moreover, majority of obese youth and adults experience psycho-social consequences of obesity For example, low self-esteem and being targeted as a victim for bullying in schools are the social outcomes of obesity for youth.30 For

4

adults, obesity results in weight bias and discrimination in employment,31psychological problems,32 not having a relationship with opposite sex in women and poor educational achievement in men.33

1.1.3 Assessments of Obesity

Overweight and obesity should ideally be defined by the amount of body fat However, the standard anthropometric measurements available to assess body fat are not ideal Better measurement techniques are complex and costly, and impractical for epidemiological research and clinical assessment.34

In clinical settings, the skin fold measurement (the measurement of subcutaneous layer of fat) is accepted as a reasonable correlate of body fat.34-37 In combination with Body Mass Index-for-age to estimate adiposity in children, skinfold measurement can improve the estimation of body fatness except in overweight (≥95th percentile) children and adolescents.38,39 However, due to differences between observers, measurement errors are common, resulting in poor reliability and reproducibility.35-37

Thus, the common, inexpensive and practical method of obesity measurement, Body Mass Index (BMI), has been recommended, based on the high reliability of measurements of height and weight.34,35,40 BMI is calculated as the child’s weight in kilograms divided by his/her height in meters, squared The limitation of this measurement is that it cannot accurately distinguish between

5

adiposity and muscularity.1,36 BMI for children also changes with age, so the BMI standard deviation scores and percentiles are more useful when tracking children and their progress Similar to BMI, another practical method which has already been widely used for screening of overweight and obesity in preschool children is weight-for-height measurement. 40,41

In research settings, one of the commonly used methods include dual energy X-ray absorptiometry (DEXA) which can measure bone mass, lean body mass and fat mass separately and the accurate percentage of body fat can be calculated.34-36 Based on a similar theory, there is a method of under-water weighing (densitometry).35 Both methods require sophisticated apparatus and complex techniques.34 Besides DEXA, other accurate, rapid, non-invasive methods include the bioelectrical impedance analysis, computed tomography (CT/CAT scan) and magnetic resonance imaging (MRI/NMR). 3, 34

1.1.4 Definition of Obesity

For adults, obesity is defined as a BMI ≥30kg/m² and overweight as a BMI between 25kg/m² to 29.99kg/m².1, 40 For children, although the BMI calculation is the same as for adults, obesity is determined based on BMI-for-age curves with percentile units, or weight-for-height curves

In addition, definition of obesity and overweight for children varies between countries.2 Two well known and commonly used definitions are from the

The IOTF attempted to define obesity cut-off points which can be accepted internationally for the purpose of a unified international definition to facilitate epidemiological research and comparison across different populations The IOTF defined percentile curves for overweight and obesity which intersect the adult cut-off points of a BMI of 25kg/m² and 30kg/m2 at age 18 years, respectively.43 The cut-off points proposed by the IOTF are age and sex specific, and are based on data from six countries: the United States, Great Britain, Hong Kong, the Netherlands, Brazil and Singapore.43

Although these cut-off points are recommended for international comparisons, the cut-offs are mainly representative of Western countries and less reflective of data from African and Asian countries.44 Moreover, data for Singapore children aged 2–6 years are not available for that dataset.43 Therefore, Singapore data was not included in the derivation of the IOTF cut-off points for children aged 2–6 years.43 Thus, the IOTF BMI cut-off points may not be applicable to preschool children in Singapore

7

BMI and body fat percentage vary across different ethnic groups.45-48Asians have a high body fat percentage with low BMI compared to Caucasians, due to differences in body composition.45,49,50 The WHO expert consultation on BMI in Asian population, held in Singapore, 2002, concluded that the current WHO BMI cut-off points may underestimate the prevalence of overweight and obesity for Asian populations based on adverse health outcomes for Asian populations, which occur at lower BMIs Asian countries were encouraged to make decisions about the definitions of increased risk for their population and WHO BMI cut-off points were used for international comparisons.45

1.1.5 Ethnic Difference

In the United States, Hispanic children are more obese than non-Hispanic black and non-Hispanic white children.26, 27, 51 Asians and Africans, except those from the Middle East and North Africa, have a lower prevalence of overweight and obesity than Western ethnic groups.52 The difference in prevalence of overweight and obesity among ethnicities may be due, in part, to differences in central fatness and muscularity, resulting in differences in body fat percentage and BMI.53 Generally, differences may be attributed to different patterns of food consumption, attitudes towards food or genetic differences

8

1.2 Prevalence of obesity across countries

1.2.1 Methodology of literature review

Using the PubMed database, I searched “prevalence AND (overweight OR obesity) AND preschool children” and total of 2,218 articles were found I narrowed down the topic search to “prevalence of overweight and obesity study in preschool children” and found 865 articles After that, I chose the titles related to the topics and found 63 articles Next, I read through all the abstracts of these and retrieved 8 of the best articles There were in total of 1,287 articles in the Scopus database and I followed the same method of literature review in PubMed database and finally, found 1 new good article from the Scopus database

1.2.2 Asian countries

A population-based study of the prevalence of obesity in preschool children was conducted in China in 2000 Liu et al (2007)54 found a prevalence of 7.4% of overweight and obesity in a large population of 262,738 preschool children aged 3.5–6.4 years The study areas were the northern rural, southern rural and southern urban areas Children who were born between 1993 and 1996

to a mother residing in one of these areas for at least one year were included The response rate was not mentioned The study used international age- and gender-specific BMI cut-off points to compare with other countries and found that the

9

prevalence of obesity is similar to that of Great Britain or the United States in the 1980s or earlier

In 2000, according to data obtained from the National Nutritional Survey,

de Onis and Blossner analysed 2,854,677 children from 94 developing countries, and found that the prevalence of obesity in <5 years old children was 3.3%.55Latin America and the Caribbean had the highest prevalence of 4.4%, with 3.9%

in Africa, and Asia contributed 2.9% which was the third highest prevalence But

in absolute numbers, 60% of overweight children from developing countries lived

in Asia This study analysed only nationally representative surveys from various developing countries which were conducted between 1985 and 1998 But there were no standardized equipment or measurement techniques between countries

In 2008, Ibrahim et al conducted a prevalence study of obesity in preschool children aged 3–6 years (n=1,695) in Jordan.56 The children were randomly selected from paying nurseries of both rural and urban areas which constituted 2.1% of the total paying nurseries in Jordan The study reported the prevalence of obesity as 20.8% in boys and 19.1% in girls and overweight was 3.8% in boys and 7.2% in girls, by using the reference of Cole et al This study showed that the prevalence of obesity was higher than overweight in the Jordan preschool children Moreover, the mean BMI of children participating in this study was equivalent to the 75th percentile of the CDC/WHO reference value Although the author mentioned that the ratio of children attending these paying nurseries to those attending governmental free nurseries equalled 15:1, the study

10

did not include children who did not go to any nursery or children who were attending the governmental free nurseries Therefore, this study is not representative

1.2.3 Non-Asian countries

Ogden et al (2010) (n=3,281), reported that in the United States, 10.4% of children aged 2 to 5 years were at or above the 95th percentile, and 21.2% of those were at or above 85th percentile, using the 2000 CDC sex-specific BMI for age growth charts.57 This study derived data from the National Health and Nutrition Examination Survey (NHANES) The survey was a nationally representative survey and aimed to evaluate the health and nutritional status of children and adults.58 The response rate for NHANES 2007-2008 was 82.1% Overall, among

2 to 5 years old children, there was no statistically significant difference between genders at these BMI for age percentiles

In Canadian preschool children between 3 and 5 years of age, the prevalence of overweight or obesity was 25.6% (Canning et al.) (2004).59 A total

of 4,161 children were selected from the population born in 1997 and subsequently enrolled in the preschool health check program in 2002 It was the first province-wide report in Canada with a good response rate of 73–84% The author also reported that there were no significant differences between gender and age groups

11

Kalies et al., in 2002, reported that the prevalence of obesity between 5–6 years old children was 2.8% in Bavaria, the largest and the second most populated state of Germany.60 This study was based on a huge number of children (126,083) from the school entry health examination and had a very high response rate of 97.1% In comparison with countries with the same definition of obesity, the prevalence of obesity in Germany was lower than that in the United States and Australia.60

There were two studies in Chile: a study in 2008 of children aged 2 to 5 years (n=25,013) by Stanojevic et al., with a prevalence of 16.4%61 and one in

2002 by Kain et al., with a prevalence of 14.7% in boys and 15.8% in girls in a group of 6 years old children (n=199,444).62 These two studies did not mention the response rates In the 2008 study, the sample selection was taken from low and middle income families and children who attended the Junta Nacional de Jardines Infantiles (JUNJI) program whereas in the second study, the samples were of the children who entered the first grade So, both studies might not be representative of the Chilean population.61,62 The study in 2002 described that the prevalence had increased between 1987 and 2000 whereas the 2008 study showed that the prevalence remained constant during the previous nine years

In an Italian study (n=2,150) conducted by Maffeis et al (2006), 8% of children aged 2–6 years were obese.63 Although it was the first study that provided international comparisons by analysing the data with three different cut-off points, it was not population based due to random selection of children from

12

the registers of kindergartens located in both urban and rural areas But this study showed a good response rate of 89.6% The authors also showed that the prevalence in Italian preschool children was as high as in the United States

1.2.4 Limitations to comparisons between countries

However, these studies could not be compared because they were conducted in different ways First, most of the studies did not mention the response rates Therefore, we do not know if there is any non-response bias Second, non-population-based studies may not represent the population at large, and cannot be compared with population-based studies Third, the sampling techniques were different among these studies Moreover, some studies used the existing data from other programmes together with new data When height and weight were measured in these studies, the equipment and measurement techniques used were not the same and not standardized from one study to another The last limitation was that different references were used to define obesity in each study and some studies did not describe the overall prevalence but they described it according to gender Therefore, all the studies were not comparable, but comparison between groups with the same cut-off points could

be summarized

13

1.2.5 Summary of the studies, comparing with the same definition

There were two studies using both CDC and IOTF definitions to compare the prevalence of obesity with other countries One study was from Chile (2002)62and the other was from Italy (2006)63 In both studies, the prevalence of obesity with the CDC definition (14.7% in boys and 15.8% in girls in the Chilean study and 16% in the Italian study) was higher than that the IOTF definition (7.2% in boys and 7.5% in girls in the Chilean study and 8% in the Italian study)

The studies using the CDC definition were from Chile (2008)61, the Italian study mentioned above63, and one from the United States57 A comparison of these studies showed that Chile had the highest prevalence (16.35%)61 followed

by the studies from Italy (16.0%)63 and the United States (10.4%)57 Although there were six studies using the International Obesity Task Force (IOTF) criteria for the definition of obesity, only three studies compared the prevalence of obesity because the other three studies described according to gender Among the three studies mentioning the prevalence, the same study from Italy had the highest prevalence of obesity (8%)63, followed by China (7.4%)54, and Germany had the lowest prevalence (2.8%)60

Another three studies reported the prevalence by gender; the highest prevalence of 20.8% (boys) and 19.1% (girls) were found in Jordan.56 The second highest were from the study of Canada with 7.8% (boys) and 8.2% (girls)59, followed by 7.2% (boys) and 7.5% (girls) from Chile62

14

For gender, two studies from China (2000) and Chile (2008) showed that the prevalence of overweight or obesity for girls was higher than for boys.54,61However, the study from Jordan showed that overweight was more common in girls than in boys but obesity was more common in boys than in girls.56 Moreover,

no significant difference in gender was seen in the United States57 and Canadian study.59 However, the studies from Germany60 and Chile62 showed that although there were no significant difference in obesity, the prevalence of overweight was higher in girls than boys

There were also three studies describing prevalence by the age group Among the three studies, the studies from Canada (2004)59 reported that the prevalence by age was not significantly different However, the gradual increment

of obesity prevalence was seen in the study from Chile (2008)61 and the reverse trend was seen in the study from China (2000)54

both rural and urban

3.5-6.4 year

262,738 Not mentioned Standardized

measurement

by locally trained health workers

Obesity-Centiles

corresponding to BMI 30kg/m2

Overweight-

Centiles corresponding to BMI 25kg/m2

Data obtained from National Nutritional Surveys from

3.3% ( all developing countries) 2.9%(Asia) 3.9%(Africa) 4.4%(Latin America)

3-6 year 1695 Not mentioned Standard procedure

by five well trained anthropometrists

Obesity-

BMI >97thpercentile

Overweight-

BMI >95 th to

97th percentile

20.8% (boys) 19.1% (girls)

3.8% (boys) 7.2% (girls)

(2010)

United States NHANES

2007-2008

2 -5 year

3281 82.1% Using CDC

measurement guidelines by trained interviewers

in 2002

3 – 5 year

4161 73%-84% Using

standardized procedure by the public health nurses

Obesity-Centiles of

BMI 30kg/m 2

Overweight-

Centiles of BMI 25kg/m2

5 – 6 year

126,083 97.1% Examined by

trained medical personal

Obesity

Centiles corresponding to BMI 30kg/m 2

Overweight-

Centiles corresponding to BMI 25kg/m2

2 – 5 year

25,013 (2004)

Not mentioned By classroom

teachers trained

by nutritionist from JUNJI program

Obesity- BMI

≥ 95th percentile

Overweight-BMI >

85th but < 95thpercentile

16.35%

(2004)

21.64% (2004)