Background
Obesity is a global epidemic and children are the worst affected with an estimated ten percent of school-aged children being overweight and one quarter of these being obese worldwide
Methods
Design, setting and sample
A population-based cross-sectional study, the Nutritional Assessment among School-going Children in Lahore, Pakistan (NASCL study), was conducted among primary school children aged five to twelve years in 2009-10. Lahore is the capital of Pakistan's most populous province Punjab and a metropolis with multiethnic populations. It has a population of nine million, including 2.5 million primary school children, and 81% of the population resides in urban area (Administrative data, Government of Punjab, 2010).
A stratified multistage random cluster sample of 1860 children aged five to twelve years in twelve primary schools of City District Lahore was enrolled. Stratified sampling, based on the population and educational system characteristics, was used to have proportionate representation of gender, area of residence and socioeconomic status (SES). About 1200 public and 1100 private primary schools in Lahore registered with the Punjab Department of Education were listed. The listed schools were stratified according to the geographic area and monthly fee structure of schools into following four strata: a) urban with high SES (urban area and fee > 2500 PKR), b) urban with middle SES (urban area and fee = 1000-2500 PKR), c) urban with low SES (urban area and fee < 1000 PKR), and d) rural with low/disadvantaged SES (rural area and fee ~100 PKR or free). The former two strata included private (including public-private mix) schools and the later two strata included public schools. In Pakistan, public schools cater low SES urban and rural children while high and middle SES urban children are educated in private and public-private mix schools. Three schools were selected at random from each stratum and contacted by the Departments of Education and Health to participate voluntarily in the study. If school administration refused to participate, next school was selected randomly from the respective stratum. For each school, a list of all classes in five grades (one to five) was obtained and one class in each grade was selected at random. In this way, sixty classes, five from each school, were selected. For each of the selected classes, first thirty-one children on class attendance register, present on data collection day and aged five to twelve years, were included in the study. Children suffering from any known metabolic syndrome (like Prader-Willi syndrome) and those not willing to participate in the study were excluded. Sample size was calculated using Epi Info 6.04d (United States' Centers for Disease Control and Prevention, 2004) with a confidence (1-α) of 95%, anticipated prevalence of 5% and margin of error of ± 1. The minimum sample size calculated was 1823 and a sample of 1860 was deemed sufficient.
Data Collection
The sampled schools were visited on pre-arranged dates in summer 2009 by a team of trained senior medical students lead by the Principal Investigator. Health education of children and teachers was also carried out after data collection in the respective school. Height was measured by portable stadiometers that were standardized and calibrated before the measurements. Feet were placed together with heels, buttocks and shoulder blades against the stick and head was positioned in the Frankfurt horizontal plane. WC and hip circumference (HC) were measured according to the World Health Organization (WHO) recommendations
Demographic information of all officially enrolled students in the sampled classes was obtained before data collection that included gender, date of birth, residential address and parental education. If demographic information of students was not found on official rosters, it was obtained from the classroom teachers. Parental education level was based on the parent with the highest total years of schooling and neighborhood income level was based on the approximate income estimate of child's residential area obtained from the Revenue Department of City District Government Lahore. Quality control measures and good practices including training, pre-testing the processes and materials, field monitoring of data collection, logistics management and daily meetings of the study teams were ensured. Informed consent statement was printed on the study form. Verbal informed consent for the child to participate in the study was taken from class teachers and school heads. As the study involved no invasive procedure, verbal informed consent was deemed sufficient. The study was approved by the Ethical Review Board of Allama Iqbal Medical College, Lahore. Permissions to conduct the survey were granted by the Punjab Departments of Education and Health, and the sampled schools.
Statistical Analysis
Data were entered and analyzed by manual and computerized checking using SPSS version 18.0 (SPSS Inc. Chicago IL, United States, 2009). Age was calculated to the precise day by subtracting the date of birth from the date of examination. Smoothed age- and gender-specific percentile curves were constructed for WC, WHR and WHtR by the LMS method
Results
The study included a sample of 1860 primary school children aged five to twelve years. The male-female ratio was 1.11 with 52.5% boys and 47.5% girls. The sample involved 20% children from each grade and 25% children from each area and SES stratum. Seventy-five percent children were urban and 25% were rural. The median age (range) was 101.2 (60-154) months. The mean and standard deviation (SD) for WC, HC, height, WHR and WHtR were 58.4 (7.9) cm, 67.2 (11.4) cm, 128.4 (11.4) cm, 0.88 (0.17) and 0.46 (0.05) respectively. Age- and gender-specific mean (SD) WC, WHR and WHtR are presented in Table
Mean and standard deviation (SD) for waist circumference (WC), waist-hip ratio (WHR) and waist-height ratio (WHtR) of Pakistani primary school children aged five to twelve years (n = 1860)
n
WC (cm)
WHR
WHtR
Boys (n = 977)
5 years (61-71 months)
84
54.0 (5.8)
0.89 (0.04)
0.46 (0.04)
6 years (72-83 months)
161
54.0 (5.6)
0.89 (0.04)
0.46 (0.04)
7 years (84-95 months)
160
55.8 (5.8)
0.88 (0.04)
0.45 (0.05)
8 years (96-107 months)
158
58.3 (6.6)
0.88 (0.04)
0.45 (0.04)
9 years (108-119 months)
161
60.8 (7.9)
0.88 (0.05)
0.45 (0.05)
10 years (120-131 months)
147
62.7 (9.8)
0.88 (0.05)
0.45 (0.06)
11 years (132-143 months)
69
62.0 (7.2)
0.88 (0.06)
0.45 (0.05)
12 years (144-155 months)
37
61.2 (5.6)
0.87 (0.04)
0.44 (0.03)
Girls (n = 883)
5 years (61-71 months)
72
52.6 (3.4)
0.86 (0.05)
0.46 (0.03)
6 years (72-83 months)
143
54.4 (6.0)
0.85 (0.05)
0.46 (0.04)
7 years (84-95 months)
157
57.0 (7.2)
0.87 (0.08)
0.46 (0.05)
8 years (96-107 months)
159
58.7 (7.0)
0.86 (0.06)
0.46 (0.05)
9 years (108-119 months)
151
61.6 (8.3)
0.86 (0.06)
0.46 (0.06)
10 years (120-131 months)
120
62.3 (8.9)
0.84 (0.06
0.45 (0.06)
11 years (132-143 months)
62
62.3 (8.4)
0.80 (0.06)
0.43 (0.05)
12 years (144-155 months)
19
62.6 (7.9)
0.81 (0.05)
0.43 (0.04)
Age- and gender-specific WC percentiles [Table
Age- and gender-specific smoothed waist circumference (WC) percentiles for Pakistani primary school children aged five to twelve years (n = 1860)
Percentiles
3 rd
5 th
10 th
25 th
50 th
75 th
90 th
95 th
97 th
Boys (n = 977)
5 years (61-71 months)
45.7
46.4
47.4
49.4
52.1
55.3
59.1
61.9
64.1
6 years (72-83 months)
46.7
47.4
48.5
50.7
53.6
57.2
61.5
64.6
67.1
7 years (84-95 months)
47.7
48.5
49.7
52.1
55.3
59.4
64.1
67.7
70.5
8 years (96-107 months)
48.8
49.6
51.0
53.6
57.1
61.6
66.9
70.9
74.0
9 years (108-119 months)
49.7
50.6
52.1
54.9
58.8
63.7
69.5
74.0
77.5
10 years (120-131 months)
50.5
51.4
53.0
56.1
60.3
65.6
72.0
76.9
80.7
11 years (132-143 months)
51.1
52.1
53.8
57.1
61.6
67.4
74.2
79.5
83.6
12 years (144-155 months)
51.5
52.6
54.4
58.0
62.8
68.9
76.2
81.9
86.2
Girls (n = 883)
5 years (61-71 months)
45.8
46.4
47.4
49.3
51.8
54.7
58.0
60.4
62.1
6 years (72-83 months)
46.7
47.4
48.5
50.7
53.6
57.1
61.0
63.9
66.0
7 years (84-95 months)
47.7
48.5
49.8
52.2
55.5
59.6
64.3
67.7
70.4
8 years (96-107 months)
48.7
49.6
51.0
53.8
57.5
62.2
67.6
71.8
74.9
9 years (108-119 months)
49.6
50.5
52.2
55.2
59.4
64.7
70.9
75.7
79.4
10 years (120-131 months)
50.2
51.3
53.0
56.4
61.0
66.9
74.0
79.4
83.6
11 years (132-143 months)
50.6
51.8
53.7
57.4
62.5
69.0
76.8
82.8
87.4
12 years (144-155 months)
50.9
52.2
54.3
58.3
63.8
70.9
79.4
85.9
91.0
Smoothed waist circumference (WC) percentile curves for Pakistani primary school boys (n = 997) and girls (n = 883) aged five to twelve years
Smoothed waist circumference (WC) percentile curves for Pakistani primary school boys (n = 997) and girls (n = 883) aged five to twelve years.
Age- and gender-specific smoothed waist-hip ratio (WHR) percentiles for Pakistani primary school children aged five to twelve years (n = 1860)
Percentiles
3 rd
5 th
10 th
25 th
50 th
75 th
90 th
95 th
97 th
Boys (n = 977)
5 years (61-71 months)
0.82
0.83
0.84
0.86
0.89
0.92
0.94
0.96
0.97
6 years (72-83 months)
0.81
0.82
0.84
0.86
0.89
0.92
0.94
0.96
0.97
7 years (84-95 months)
0.80
0.81
0.83
0.86
0.88
0.91
0.94
0.96
0.97
8 years (96-107 months)
0.80
0.81
0.82
0.85
0.88
0.91
0.94
0.96
0.97
9 years (108-119 months)
0.79
0.80
0.82
0.85
0.88
0.91
0.94
0.96
0.97
10 years (120-131 months)
0.78
0.79
0.81
0.84
0.88
0.91
0.94
0.96
0.97
11 years (132-143 months)
0.77
0.79
0.81
0.84
0.88
0.91
0.94
0.96
0.97
12 years (144-155 months)
0.77
0.78
0.80
0.84
0.87
0.91
0.94
0.96
0.97
Girls (n = 883)
5 years (61-71 months)
0.76
0.77
0.79
0.82
0.85
0.89
0.93
0.95
0.97
6 years (72-83 months)
0.76
0.77
0.79
0.82
0.86
0.9
0.93
0.96
0.97
7 years (84-95 months)
0.76
0.77
0.79
0.82
0.86
0.9
0.94
0.96
0.98
8 years (96-107 months)
0.75
0.76
0.78
0.82
0.86
0.9
0.94
0.97
0.98
9 years (108-119 months)
0.75
0.76
0.78
0.81
0.85
0.89
0.93
0.96
0.98
10 years (120-131 months)
0.73
0.74
0.76
0.79
0.83
0.88
0.92
0.95
0.97
11 years (132-143 months)
0.72
0.73
0.74
0.78
0.82
0.86
0.90
0.93
0.95
12 years (144-155 months)
0.70
0.71
0.73
0.76
0.80
0.84
0.89
0.92
0.94
Smoothed waist-hip ratio (WHR) percentile curves for Pakistani primary school boys (n = 997) and girls (n = 883) aged five to twelve years
Smoothed waist-hip ratio (WHR) percentile curves for Pakistani primary school boys (n = 997) and girls (n = 883) aged five to twelve years.
Age- and gender-specific smoothed waist-height ratio (WHtR) percentiles for Pakistani primary school children aged five to twelve years (n = 1860)
Percentiles
3 rd
5 th
10 th
25 th
50 th
75 th
90 th
95 th
97 th
Boys (n = 977)
5 years (61-71 months)
0.40
0.41
0.42
0.44
0.46
0.49
0.52
0.54
0.56
6 years (72-83 months)
0.40
0.40
0.41
0.43
0.46
0.49
0.52
0.54
0.56
7 years (84-95 months)
0.39
0.39
0.40
0.43
0.45
0.48
0.52
0.54
0.56
8 years (96-107 months)
0.38
0.39
0.40
0.42
0.45
0.48
0.52
0.54
0.56
9 years (108-119 months)
0.37
0.38
0.39
0.42
0.45
0.48
0.52
0.54
0.56
10 years (120-131 months)
0.37
0.37
0.39
0.41
0.44
0.48
0.52
0.54
0.56
11 years (132-143 months)
0.36
0.37
0.38
0.41
0.44
0.48
0.52
0.54
0.56
12 years (144-155 months)
0.35
0.36
0.38
0.40
0.44
0.48
0.52
0.54
0.56
Girls (n = 883)
5 years (61-71 months)
0.39
0.40
0.41
0.43
0.45
0.48
0.51
0.53
0.54
6 years (72-83 months)
0.39
0.39
0.41
0.43
0.45
0.48
0.51
0.53
0.55
7 years (84-95 months)
0.38
0.39
0.40
0.43
0.45
0.48
0.52
0.54
0.56
8 years (96-107 months)
0.38
0.39
0.40
0.42
0.45
0.49
0.52
0.55
0.57
9 years (108-119 months)
0.38
0.38
0.40
0.42
0.45
0.49
0.53
0.55
0.58
10 years (120-131 months)
0.37
0.38
0.39
0.41
0.44
0.48
0.53
0.56
0.58
11 years (132-143 months)
0.36
0.37
0.38
0.41
0.44
0.48
0.53
0.56
0.59
12 years (144-155 months)
0.35
0.36
0.37
0.40
0.43
0.47
0.52
0.56
0.60
Smoothed waist-height ratio (WHtR) percentile curves for Pakistani primary school boys (n = 997) and girls (n = 883) aged five to twelve years
Smoothed waist-height ratio (WHtR) percentile curves for Pakistani primary school boys (n = 997) and girls (n = 883) aged five to twelve years.
Comparison of fiftieth waist circumference (WC) percentile curves for Pakistani primary school boys (a) and girls (b) aged five to twelve years with previous studies that measured WC at the same site
Comparison of fiftieth waist circumference (WC) percentile curves for Pakistani primary school boys (a) and girls (b) aged five to twelve years with previous studies that measured WC at the same site. WC was measured midway between the lowest rib and the superior border of iliac crest, in accordance with the WHO recommendations.
Age- and gender-specific eighty-fifth percentile values for waist-height ratio (WHtR) corresponding to cut-off value of 0.5 for defining central obesity among Pakistani primary school children aged five to twelve years (n = 1860)
Age
Boys (n = 997)
Girls (n = 883)
5 years (61-71 months)
0.507
0.499
6 years (72-83 months)
0.504
0.500
7 years (84-95 months)
0.502
0.504
8 years (96-107 months)
0.501
0.507
9 years (108-119 months)
0.501
0.508
10 years (120-131 months)
0.501
0.507
11 years (132-143 months)
0.501
0.504
12 years (144-155 months)
0.500
0.500
Twelve percent children (95% CI 10.1-13.0) had a WC ≥90th percentile and 16.5% children (95% CI 14.7-18.1) had a WHtR ≥0.5 while 11% children (95% CI 8.9-11.6) had both WC ≥90th percentile and WHtR ≥0.5. Prevalence of central obesity significantly increased with grade among both boys and girls [Table
Grade- and Gender-specific prevalence of central obesity among Pakistani primary school children aged five to twelve years (n = 1860)
WC ≥90th percentile
WHtR ≥0.5
Centrally Obese a
(n = 213)
(n = 304)
(n = 189)
n (%)
P Value
n (%)
P Value
n (%)
P Value
Boys (n = 997)
103 (10.5)
156 (16.2)
93 (9.5)
Grade one (n = 233)
19 (8.2)
0.054
50 (21.5)
0.026
16 (6.9)
0.033
Grade two (n = 187)
13 (7.0)
23 (12.3)
11 (5.9)
Grade three (n = 183)
18 (9.8)
23 (12.6)
17 (9.3)
Grade four (n = 184)
26 (14.1)
35 (19.0)
25 (13.6)
Grade five (n = 190)
27 (14.2)
25 (13.2)
24 (12.6)
Girls (n = 883)
148 (16.8)
110 (12.5)
96 (10.9)
Grade one (n = 139)
16 (11.5)
0.004
20 (14.4)
< 0.001
13 (9.4)
0.001
Grade two (n = 185)
11 (5.9)
15 (8.1)
7 (3.8)
Grade three (n = 189)
31 (16.4)
41 (21.7)
28 (14.8)
Grade four (n = 188)
33 (17.6)
45 (23.9)
30 (16.0)
Grade five (n = 182)
19 (10.4)
27 (14.8)
18 (9.9)
a≥90th age- and gender-specific waist circumference (WC) percentile and ≥0.5 waist-height ratio (WHtR)
Socio-demographic correlates of central obesity among Pakistani primary school children aged five to twelve years (n = 1860)
Total Sample (n = 1860)
Centrally Obesea (n = 189)
Characteristics
n (%)
n (%)
P Value
Gender
Boys
977 (52.5)
93 (9.5)
0.335
Girls
883 (47.5)
96 (10.9)
Grade
One
372 (20.0)
29 (7.8)
< 0.001
Two
372 (20.0)
18 (4.8)
Three
372 (20.0)
45 (12.1)
Four
372 (20.0)
55 (14.8)
Five
372 (20.0)
42 (11.3)
Area and socioeconomic status (SES)
Urban with high SES
465 (25.0)
101 (21.7)
< 0.001
Urban with middle SES
465 (25.0)
58 (12.5)
Urban with low SES
465 (25.0)
28 (6.0)
Rural (low/disadvantaged SES)
465 (25.0)
2 (0.4)
Neighborhood income
Low
651 (35.0)
27 (4.1)
< 0.001
Middle
910 (48.9)
97 (10.7)
High
299 (16.1)
65 (21.7)
Parental education
Illiterate
366 (19.7)
6 (1.6)
< 0.001
High school
496 (26.7)
25 (5.0)
College
531 (28.5)
71 (13.4)
Higher education
467 (25.1)
87 (18.6)
a≥90th age- and gender-specific waist circumference (WC) percentile and ≥0.5 waist-height ratio (WHtR)
Logistic regression analysis of socio-demographic factors associated with central obesity among Pakistani primary school children aged five to twelve years (n = 1860)a, b
Characteristics
Crude OR
(95% CI)
P Value
Adjusted OR
(95% CI)
P Value
Grade
One
Reference
-
Reference
-
Two
0.70 (0.37-1.31)
0.259
0.80 (0.41-1.56)
0.515
Three
2.29 (1.24-4.22)
0.008
3.15 (1.54-6.45)
0.002
Four
3.36 (1.66-6.80)
0.001
5.47 (2.25-13.31)
< 0.001
Five
2.84 (1.23-6.54)
0.014
5.11 (1.76-14.85)
0.003
Area and socioeconomic status (SES)
Urban with high SES
64.24 (15.74-262.13)
< 0.001
82.34 (15.76-430.31)
< 0.001
Urban with middle SES
32.99 (8.01-135.92)
< 0.001
35.67 (6.95-183.18)
< 0.001
Urban with low SES
14.83 (3.51-62.64)
< 0.001
13.67 (2.86-65.40)
0.001
Rural (low/disadvantaged SES)
Reference
-
Reference
-
Neighborhood income
Low
0.16 (0.10-0.25)
< 0.001
1.50 (0.77-2.93)
0.239
Middle
0.43 (0.30-0.61)
< 0.001
0.77 (0.51-1.17)
0.220
High
Reference
-
Reference
-
Parental education
Illiterate
Reference
-
Reference
-
High school
3.37 (1.36-8.31)
0.008
0.73 (0.26-2.03)
0.545
College
9.93 (4.25-23.20)
< 0.001
1.04 (0.37-2.91)
0.938
Higher education
14.13 (6.09-32.77)
< 0.001
1.32 (0.47-3.73)
0.599
aThe model is controlled for age and gender
b≥90th age- and gender-specific waist circumference (WC) percentile and ≥0.5 waist-height ratio (WHtR)
Linear regression analysis of socio-demographic factors with waist circumference (WC) among Pakistani primary school children aged five to twelve years (n = 1860)a, b
Characteristics
Regression coefficient
(95% CI)
Standard error
P value
Grade
1.099 (0.686 to 1.511)
0.210
< 0.001
Area and SESc
-1.896 (-2.360 to -1.431)
0.237
< 0.001
Higher neighborhood income
-0.049 (-0.690 to 0.591)
0.326
0.880
Higher parental education
0.428 (0.018 to 0.839)
0.209
0.041
aThe model is controlled for age and gender
bR2 for model = 0.280
cArea and SES strata: 1. Urban with high SES, 2. Urban with middle SES, 3. Urban with low SES, and 4. Rural with low/disadvantaged SES
Linear regression analysis of socio-demographic factors with waist-height ratio (WHtR) among Pakistani primary school children aged five to twelve years (n = 1860)a, b
Characteristics
Regression coefficient
(95% CI)
Standard error
P value
Grade
-0.001 (-0.004 to 0.002)
0.001
0.428
Area and SESc
-0.010 (-0.013 to -0.006)
0.002
< 0.001
Higher neighborhood income
-0.004 (-0.009 to 0.001)
0.002
0.056
Higher parental education
0.004 (0.001 to 0.007)
0.001
0.012
aThe model is controlled for age and gender
bR2 for model = 0.068
cArea and SES strata: 1. Urban with high SES, 2. Urban with middle SES, 3. Urban with low SES, and 4. Rural with low/disadvantaged SES
Discussion
First ever age- and gender-specific smoothed percentiles for WC, WHR and WHtR developed from a representative sample of 1860 Pakistani primary school children aged five to twelve years are presented. These charts are based on WC measured midway between the lowest rib and the superior border of iliac crest, in accordance with the WHO recommendations
WC increased with age among both boys and girls, consistent with previous literature
Eleven percent of children were centrally obese. Central obesity showed a significantly increasing trend with grade among both boys and girls and higher grade independently predicted the risk of being centrally obese and having higher WC. These findings are consistent with previous studies reporting higher obesity prevalence in older children
Variability in the data ascertainment may have introduced an error into the estimates; however, we do not anticipate large or systematic differences. The effects of puberty on anthropometric indices were not explored in the present study; however, future studies are suggested in this regard. Cross-sectional nature of the study should be considered when interpreting the findings reported and future longitudinal studies are warranted to establish the temporal nature and causality of these associations. These findings can be generalized to South Asian primary school children that share the same genetic and environmental factors with the sample.
Conclusions
Comprehensive worldwide reference values are needed to establish an internationally accepted age-, gender-, and ethnicity-specific definition of central obesity. The present study is the first one to report anthropometric indices predictive of central obesity for Pakistani school-aged children. Eleven percent children were centrally obese and strong predictors included higher grade, urban area with high SES and higher parental education. These findings support the need for developing a National strategy for childhood obesity and implementing targeted interventions, prioritizing the higher social class and involving communities.
Competing interests
The authors declare that they have no competing interests.
Authors' contributions
MUM, principal investigator, conceived and implemented the study, analyzed and interpreted the data, prepared the manuscript and supervised the entire project. SG and HMA contributed to the study analysis, interpretation and manuscript preparation. US contributed to the study conception, implementation and analysis. MAS and JA oversaw the study conception, implementation and manuscript preparation. All authors read and approved the final manuscript.