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Indian Pediatr 2011;48:
523-528 |
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Growth Pattern of Schoolchildren in Sagamu,
Nigeria Using the CDC Standards and 2007 WHO Standards |
MB Fetuga, TA Ogunlesi, AF Adekanmbi and AD Alabi
From the Departments of Pediatrics, and Community
Medicine and Primary Care,
Olabisi Onabanjo University, Sagamu, Nigeria.
Correspondence to: Dr TA Ogunlesi, PO Box 652, Sagamu
121001NG, Ogun State, Nigeria.
Email:
[email protected]
Received: January 20; 2010,
Initial review: February 9, 2010;
Accepted: June 1, 2010.
Published
online: 2010 November 30.
PII: S09747559100042-1
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Objective: To compare the median weight, height and body mass index of
school children with the 2000 CDC and 2007 WHO reference values.
Settings: Schoolchildren in Sagamu, Nigeria.
Design: Cross-sectional survey.
Methods: Between November and December, 2008, 1690
school children aged 6 to 16 years from 8 primary schools were surveyed
using multi-stage sampling methods. The weight, height and body mass index
(BMI) were recorded for each child. The Z-scores of the median
anthropometric parameters for each age and sex were determined with the
LMS statistical method using the values of L, M and S provided on the CDC
and WHO charts.
Results: The weight, height and BMI Z-scores were
less than the reference values provided on the CDC and WHO charts but were
generally closer to the WHO standards compared to the CDC standards. The
median weight, height and BMI for females generally plotted higher on CDC
and WHO chart compared to the males. The prevalence of underweight and
stunting were relatively lower while the prevalence of overweight and
obesity was relatively higher among children aged 6 to 10 years using the
WHO references compared to the CDC reference values.
Conclusions: The WHO references would
under-diagnose under-nutrition and over-diagnose overweight/obesity in the
population studied.
Key words: Growth pattern, Growth standards, Children, Nigeria,
School-age.
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G rowth pattern of children
and adolescents in Sagamu, Southwest Nigeria has not been studied in the
recent past. Growth parameters of children are usually interpreted in
relation to international standards like the NCHS and CDC Growth Charts of
1977 and 2000, respectively. In 2007, the World Health Organisation
published a new set of growth charts believed to be applicable to children
reared healthily in all parts of the globe. These standards were derived
from prospectively collected data from exclusively breastfed children of
non-smoking mothers from the developed and developing parts of the world.
The population of children studied in Sagamu were
reared by non-smoking mothers and the exclusive breastfeeding rate for the
first 3 to 6 months of life ranged from 26% to 58% (Personal
communication). Therefore, this population of school children was fairly
comparable to the international reference populations from which CDC [1,2]
and WHO standards [3] were derived.
The objective of the study was to determine the age and
sex specific mean and median values of weight, height and body mass index
of children aged 6 to 16 years in Sagamu, Nigeria and compare with the
2000 CDC standard values and the 2007 WHO standard values.
Methods
This cross-sectional survey was carried out in Sagamu
Local Government Area of Ogun State, Southwest Nigeria between November
and December 2008. The local government area is made up of 15 political
wards with the headquarters in Sagamu township. There were 167 public and
private primary schools in Sagamu Local Government Area with total school
enrolment of 26, 547 children as at 2007.
The sample size was determined using the prevalence of
underweight in a Nigerian population similar to the one under study [4],
and was calculated to be 364 but 1,690 were studied to allow for
precision. No attrition was recorded as all the recruited pupils
participated in the study. Multi-stage sampling technique was adopted for
the survey. In the first stage of the sampling, 8 geo-political wards
(equivalent of districts) were randomly selected from the existing 15
wards (by balloting). In the second stage, one primary school was randomly
selected from the schools in each of the selected wards (8 out of a total
of 78 primary schools). In the third stage, all the children aged 6 to 16
years in each of the elected schools were identified and their total
numbers in each school was determined. Thereafter, proportionate method
was used to determine the number required to be sampled from each school
using simple ratios in order to arrive at the targeted sample size of
1,690. Ethical approval was obtained from the Ethics and Scientific Review
Committee of the Olabisi Onabanjo University Teaching Hospital, Sagamu and
permissions were obtained from the relevant Education Authorities in the
Local Government Area. Assent was obtained from the parents of the
selected children.
The subjects were apparently healthy school-children
and adolescents, aged 6 to 16 years who were randomly selected
proportionately from the selected schools. Those with physical deformities
and chronic debilitating diseases were excluded. Age to the nearest year
was obtained from the school records. Weight was recorded using a portable
spring balance weighing scale (Camry, England), calibrated in 0.5 kg and
was standardized daily with known weights. The height was measured with a
steel tape measure calibrated in metres and to the nearest centimetre
using recommended procedures [5]. Inter-observer variability was minimized
by ensuring zero-correction before every measurement, not more than one
person measured either weight or height in a particular population and
teachers in the schools served as independent observers to verify
measurements occasionally.
The mean and median weight, height and BMI (wt in
kg/height in m2) were calculated for
each age and sex. The median weight, height and BMI were standardized by
converting them to Z-scores (SD) using the LMS method [6] . This was done
with the age and sex specific values of LMS for weight, height and body
mass index as provided in the 2000 CDC Growth Charts and the 2007 WHO
Growth Charts. Z-scores were used to compare data against known reference
values to facilitate interpretability by showing how distant from a
reference point is a measured parameter. Both growth charts provided
references for height and BMI for the ages under study (6 to 16 years).
While the CDC charts provided weight standards for children aged 6 to 16
years, the WHO charts only provided weight standards for ages 5 to 10
years [7] . Therefore, weight assessment was only done for children aged 6
to 10 years to allow for uniformity in the comparison with both CDC and
WHO standards.
Using the Z-scores derived from the CDC and WHO
standards, the nutritional status of the subjects (in terms of underweight
and stunting) were determined and the prevalence of each form of
malnutrition were compared. Underweight was defined as weight-for-age less
than -2SD for age and sex while stunting was defined as height-for-age
less than -2SD for age and sex [8].
In addition, overweight was defined as BMI Z-score greater than +1 SD
while obesity was defined as BMI Z-score greater than +2SD(7). Wasting was
not assessed because the WHO charts provided no data for weight-for-height
standards which could be used to diagnose wasting unlike the CDC charts.
The data were analyzed using the SPSS 15.0 statistical
software. Mean values were compared using the Student’s t-test and
P values less than 0.05 defined statistical significance.
Results
A total of 1,690 school children were studied,
comprising of 819 (48.5%) males and 871 (51.5%) females. Overall, the
males had significantly lower mean weight compared to females (25.3 kg
vs 26.5 kg; P = 0.002) and lower BMI compared to the females
(14.7kg/m2 vs 15.0kg/m2; P
= 0.007). The overall mean heights of the males and females were similar
(130 cm vs 131cm; P = 0.06).
As shown in Table I, the weight Z-scores
were closest to the mean for male and female at age 6 years on both CDC
and WHO charts. With increasing age, the difference between the weight
Z-scores on the two reference charts got closer for females but wider
for males.
TABLE I
Comparison of Median Weight (kg) Of The Study Population With The CDC And WHO Standards
Age (years) |
Males |
Females |
|
Median |
CDC* |
WHO# |
Median |
CDC* |
WHO# |
6 |
18.5 |
-0.89 |
-0.79 |
18.0 |
-0.88 |
-0.78 |
7 |
20.0 |
-1.09 |
-1.01 |
19.0 |
-1.31 |
-1.10 |
8 |
21.0 |
-1.50 |
-1.40 |
21.0 |
-1.33 |
-1.14 |
9 |
22.0 |
-1.86 |
-1.74 |
22.0 |
-1.74 |
-1.59 |
10 |
24.5 |
-1.78 |
-1.60 |
25.0 |
-1.61 |
-1.51 |
*CDC Z-scores;
#WHO Z-scores. |
Median height Z-scores for both sexes were below the
mean on the CDC and WHO reference values (Table II). The
median height Z-scores for males were closest to the CDC and WHO reference
values at age 6 years and progressively declined from age 8 years, but the
pattern was not consistent for females. The distance of the height
Z-scores below the reference values on both the CDC and WHO charts was
most pronounced between ages 12 and 16 years for males. In addition, the
median heights for females were generally closer to the CDC and WHO
reference values compared to the males’ median values. The height Z-scores
for males on the WHO charts were higher than on the CDC charts between
ages 7 and 11 years. On the other hand, the pattern for females showed
greater inconsistencies in trend.
TABLE II
Comparison of Median Height (cm) of the Study Population with the CDC and WHO Standards
Age (years) |
Males |
Females |
|
Median |
CDC* |
WHO# |
Median |
CDC* |
WHO# |
6 |
113.0 |
-0.42 |
-0.49 |
110.0 |
-0.99 |
-1.00 |
7 |
115.5 |
-1.30 |
-1.27 |
116.5 |
-0.97 |
-0.78 |
8 |
122.0 |
-1.07 |
-0.93 |
121.0 |
-1.19 |
-0.95 |
9 |
127.0 |
-1.10 |
-0.95 |
127.0 |
-1.00 |
-0.89 |
10 |
131.0 |
-1.20 |
-1.06 |
132.0 |
-0.94 |
-1.11 |
11 |
135.5 |
-1.26 |
-1.20 |
135.0 |
-1.28 |
-1.50 |
12 |
137.0 |
-1.69 |
-1.70 |
140.5 |
-1.48 |
-1.56 |
13 |
141.0 |
-1.97 |
-2.02 |
145.0 |
-1.77 |
-1.64 |
14 |
146.0 |
-2.11 |
-2.17 |
151.0 |
-1.44 |
-1.26 |
15 |
148.0 |
-2.61 |
-2.69 |
153.5 |
-1.29 |
-1.19 |
16 |
154.0 |
-2.45 |
-2.43 |
154.0 |
-1.33 |
-1.25 |
*CDC Z-scores;
#WHO Z-scores. |
The median BMI Z-scores for both sexes were below the
reference values on both CDC and WHO charts but showed no generally
consistent pattern (Table III). For the males, the BMI
Z-scores were most distant from the mean values on both CDC and WHO charts
between 12 and 16 years of age. The pattern was similar for females except
for a most pronounced reversal of the Z-scores towards the mean between 15
and 16 years of age. Generally, the Z-scores for females were higher than
those of males.
TABLE III
Comparison of Median Body Mass Index (kg/m2) of The Study Population With
The CDC and WHO Standards
Age (years) |
Males |
Females |
|
Median |
CDC* |
WHO# |
Median |
CDC* |
WHO# |
6 |
14.4 |
-0.89 |
-0.72 |
14.1 |
-0.92 |
-0.81 |
7 |
14.3 |
-1.01 |
-0.92 |
14.2 |
-0.91 |
-0.79 |
8 |
14.3 |
-1.13 |
-1.08 |
14.1 |
-1.15 |
-1.01 |
9 |
14.1 |
-1.51 |
-1.44 |
14.2 |
-1.28 |
-1.16 |
10 |
14.3 |
-1.57 |
-1.49 |
14.5 |
-1.30 |
-1.22 |
11 |
14.7 |
-1.53 |
-1.46 |
14.9 |
-1.30 |
-1.28 |
12 |
14.9 |
-1.70 |
-1.63 |
15.0 |
-1.53 |
-1.58 |
13 |
14.7 |
-2.24 |
-2.19 |
15.8 |
-1.52 |
-1.64 |
14 |
15.4 |
-2.03 |
-2.06 |
15.8 |
-1.64 |
-1.78 |
15 |
15.8 |
-2.18 |
-2.15 |
18.1 |
-0.70 |
-0.84 |
16 |
16.1 |
-2.36 |
-2.27 |
19.4 |
-0.37 |
-0.48 |
*CDC Z-scores;
#WHO Z-scores. |
Table IV shows that for children aged 6 to 10
years, the prevalence of underweight and stunting were higher in both
sexes when determined using the CDC standards compared to WHO standards.
However, for children aged 11 to 16 years, there were no differences in
the prevalence of stunting determined with either CDC or WHO standards.
Further, the prevalence of overweight/obesity was lower in both sexes when
determined with the CDC standards compared to the WHO standards from age 6
to 16 years.
TABLE IV
Prevalence of Underweight, Stunting and Overweight/Obesity among School
Children in Sagamu, Nigeria.
Age group |
Males |
|
|
Females |
6 – 10 years |
CDC (n = 479) |
WHO (n = 479) |
CDC (n = 539) |
WHO (n = 539) |
Underweight |
160 (33.4) |
145 (30.2) |
153 (28.4) |
115 (21.3) |
Stunting |
85 (17.7) |
81 (16.9) |
86 (15.9) |
63 (11.7) |
Overweight* |
9 (1.8) |
18 (3.8) |
16 (2.9) |
18 (3.3) |
11 – 16 years |
n = 342 |
n = 342 |
n = 330 |
n = 330 |
Stunting |
137 (40.0) |
138 (40.4) |
88 (26.7) |
89 (26.9) |
Overweight* |
1 (0.29) |
2 (0.58) |
1 (0.3) |
4 (1.2) |
Figures in
parentheses indicate percentages; *Overweight and obesity. |
Discussion
The present study has shown that the age- and
sex-specific median weight, height and body mass index of school children
aged 6 to 16 years in Sagamu, Southwest Nigeria were less than the mean
values on the CDC and WHO charts but were generally closer to the WHO
standards compared to the CDC standards.
Our observations are similar to findings in a previous
Nigerian study in which school children in urban areas had remarkably
lower mean weight and height compared with the NCHS reference population
[9]. It also agreed with the findings for Pakistani [10] and Malawian
children [11] who also had mean weight and height lower than the median
values of NCHS references.
Overall, the observed differences in the Z-scores of
the observed median weight, height and BMI on the CDC and WHO standards
must necessarily be taken into consideration when interpreting anthropometric
data using these standards. The observed differences in the growth
parameters and nutritional status of the population studied using the CDC
and WHO standards agreed with previous reports [12]. Therefore, the
observed lower prevalence of underweight and stunting and higher
prevalence of overweight/obesity in the 6 to 10 years group determined
with the WHO standards were expected. Although, a similarly higher
prevalence of overweight/obesity was also observed in the 11 to 16 years
group using the WHO standards, it is unclear why there was no obvious
difference in the prevalence of stunting as determined by either the CDC
or WHO standards in the 11 to 16 years group. However, this observation
implies that in the determination of nutritional status of school-age
children, attention must be paid to specific age groups as well as the
reference population applied in order to draw meaningful and comparable
conclusions.
The observed higher Z-scores for females on both the
CDC and WHO charts in addition to the higher prevalence of stunting among
males in the 6 to 10 years and 11 to 16 years groups suggested a higher
linear growth potential among females. This observation agreed with
previous reports among pre-school children in ten Sub-Saharan African
countries where increased prevalence of stunting among males was possibly
attributed to low family socioeconomic status [13]. The details of
socio-economic characteristics of the subjects were not included in the
present study. Such sex differences in linear growth were previously
reported from Bangladesh [14].
To conclude, the findings in this study imply that
using the CDC standard, more children are likely to be regarded as
abnormally short or underweight thus prompting unnecessary clinical
evaluations and interventions in an under-resourced setting. On the other
hand, many children with or at risk of overweight/obesity are likely to be
missed using the CDC standards, thus delaying diagnosis, preventing
appropriate interventions and allowing severe morbidities which are
associated with overweight/obesity. The small study size is acknowledged
as a limitation in this study and a larger multicentre study in southwest
Nigeria is recommended. However, this study has brought to the fore, the
need to comparatively evaluate the tools commonly used for growth
assessment in children.
Contributors: MBF, TAO, and AFA conceived and
designed the study; MBF, TAO and AFA collected, analysed and interpreted
data; ADA participated in data interpretation; all authors drafted the
manuscript and provided critical revision for important intellectual
content.
Funding: None.
Competing interest: None stated.
What is Already Known?
• Growth parameters of school children in most
parts of the developing world plot below the references provided by
the 2000 CDC Standards.
What This Study Adds?
• More children in Nigeria are likely to be
regarded as overweight/obese and less are likely to be regarded as
underweight and stunted using the WHO standards compared to the CDC
standards.
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