Journal of Tropical Pediatrics, 2016, 62, 345–351
doi: 10.1093/tropej/fmw004
Advance Access Publication Date: 17 March 2016
Original paper
Growth Characteristics of Contemporary
School-age Nigerian Children
by Jerome B. E. Elusiyan,1 Maryann U. Ibekwe,2 Yahaya S. Alkali,3 and
Juliana Chizo Agwu4
1
Department of Paediatrics and Child Health, Obafemi Awolowo University, PMB 13 Ile-Ife, Nigeria
2
Department of Paediatrics, Ebonyi State University, PMB 058 Abakaliki, Nigeria
3
Department of Paediatrics, Federal Medical Centre, PMB 0037 Gombe, Nigeria
4
Department of Paediatrics, Sandwell and West Birmingham NHS Trust, West Bromwich, B71 4HJ West Midlands
Correspondence: Juliana Chizo Agwu, Department of Paediatrics, Sandwell and West Birmingham NHS Trust, West Bromwich B71 4HJ, West
Midlands. E-mail <[email protected]>
ABSTRACT
Objective: There are no locally derived growth charts in Nigeria, and so, health workers rely on
international reference charts. We therefore compared the growth characteristics of 4350 school-age
Nigerian children (SNC) (2243 girls, 2107 boys) (4–16 years) from three ethnic groups (Hausa,
Igbo and Yoruba) to both the UK (UK 1990) and US (2000 CDC) reference data.
Results: Height of SNC was similar to international references at the start of school age and then
started to decline. The decline appeared to peak at 15 years for boys and 13 years for girls. At all
ages, sex, ethnicity and affluence, SNC were lighter than international references. There were significant differences in the prevalence of stunting, underweight and obesity among the three ethnic
groups (p < 0.05).
Conclusion: There is a risk of over-diagnosing short stature and underweight if health workers continue to use growth charts derived from other geographical areas.
K E Y W O R D S : growth, growth charts, stunting.
INTRODUCTION
The 2006 World Health Organization growth chart
is derived from growth data of optimally nourished
breast-fed children and therefore depicts a healthy
pattern of growth [1]. It has been adopted by >150
countries, including Nigeria, for assessing growth of
children aged 0–4 years because the main determinant of early childhood growth is nutrition, and as a
result, there is similarity in early childhood growth
among diverse ethnic groups [2, 3]. There are currently no locally derived growth charts for use in
Nigerian children >4 years of age. Health workers
rely on charts developed by the Center for Disease
Control for children in USA (2000 CDC) [4], or
the UK 1990 growth charts for British children [5].
This may not be appropriate, as growth in childhood
and adolescence differs between different ethnic
groups and countries [6]. Although nutrition remains important, the main determinants of growth
in this age-group include genetics, growth hormone
(and other hormones), as well as sex steroids.
International growth charts allow comparison between countries, but regional or national references
are more useful in assessing local changes in growth
patterns [7]. It is recommended that growth references are updated regularly, as many countries have
C The Author [2016]. Published by Oxford University Press. All rights reserved. For Permissions, please email: [email protected]
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Growth Characteristics of School-age Nigerian Children
documented positive secular trend [8]. There have
been several studies on the growth indices of children in Nigeria, but most of these are limited to either one ethnic group [9–13] or one age band [12–
15]. Many were carried out more than a decade ago
[16–18]. Few studies have sought to compare the
growth indices among the various ethnic groups.
To assess how well school-age Nigerian children
(SNC) from the three largest ethnic groups match
with or diverge from the 2000 CDC or the UK 1990
growth charts, we studied their growth characteristics
and compared their growth indices with international
growth references.
to the last completed millimeter. Weight was measured to the nearest 0.1 kg using a SECA self-zeroing
electronic scale. Height measurements were carried
out mainly by three of the authors who are trained in
standard techniques of measuring children. The
within- and between-observer error between the
three authors was 0.04 cm for stature and 0.05 kg
for weights.
STATISTICAL ANALYSIS
Sample size was calculated using standard published
equation [20]:
n ¼ Z2 P ð1 PÞ d2
ETHICS
Ethical approval was obtained from Federal
Teaching hospital Abakaliki, Ebonyi state, Federal
Medical Centre, Gombe, Gombe State and Obafemi
Awolowo University Teaching Hospitals, Ile-Ife,
Osun State. Parental consent and verbal assent from
the children were obtained before participation.
STUDY DESIGN
This cross-sectional study included SNC (4–16
years) from three ethnic groups of Hausa/Fulani,
Igbo and Yoruba recruited from local schools in
Abakaliki, Gombe and Ile-Ife. The inhabitants of
Abakaliki (southeastern Nigeria) are mainly of Igbo
ethnicity, while the inhabitants of Gombe (northeastern Nigeria) are mainly from Hausa/Fulani ethnic group. The main ethnic group in Ile-Ife
(southwestern Nigeria) is the Yoruba.
The study was carried out between April 2013
and June 2015 in eight government-funded and nine
fee-paying primary and secondary schools chosen by
multi-stage random sampling. Children present on
the day of school visitation with parental consent
were selected. Those with chronic illness or who had
been hospitalized in the preceding 6 months and
those whose birthdays could not be ascertained were
excluded. We defined affluence as attendance to a
fee-paying school.
ANTHROPOMETRY
All centers used the same type of equipment. Height
was measured by standard method [19]using a selfcalibrating Leicester Height Measure and recorded
where ‘z’ is the critical value, and in a two-tailed test,
it is equal to 1.96; p is the estimated prevalence of
stunting; and d is the absolute sampling error that
can be tolerated (which is set at 3% for this study).
Using published average prevalence of stunting for
Nigerian children of 39% [13], the minimum sample
size for each study city was determined as 1015.
Data were analyzed using Minitab 17 software
and ‘Growth Analyser RCT’ software. The mean values, standard deviation (SD) and Z score (standard
deviation score; SDS) for each age-group in relation
to both the UK 1990 growth data and the 2000
CDC reference data were calculated. Multiple regression analysis was used for factors that may affect
growth indices with p < 0.05 considered significant.
Two sample t tests were used for continuous variables, and chi square tests for categorical variables.
DEFINITIONS
Stunting was defined as height for age Z score
(HAZ) 2 SDS below the mean of 2000 CDC
reference data, while underweight is defined as body
mass index (BMI) 2 SDS below the mean of
2000 CDC reference data and Obesity as BMI 2
SDS above the mean of 2000 CDC reference data.
RESULTS
Of the 4363 children selected, 13 children were
excluded: seven from Abakaliki (two had sickle cell
disease, four were absent on day of measurement
and one refused measurement), five from Gombe
(one was hospitalized on day of measurement, two
Growth Characteristics of School-age Nigerian Children
relocated to another town and in two, parents withdrew consent) and one from Ile-Ife (child refused
measurement). In all, 4350 children completed the
study (Table 1).
Boys were significantly taller than girls at ages 4,
5, 15 and 16, and girls were significantly taller than
boys at age 10 (p < 0.05). The difference between
the median heights for age showed that linear growth
appeared to accelerate between the age of 13 and 14
years in girls and 15 and 16 years in boys.
COMPARISON WITH 2000 CDC AND UK
1990 REFERENCES
Nigerian girls had a mean height of 0.3 SDS and
mean BMI of 0.8 SDS compared with US and UK
references, respectively. Nigerian boys had mean
height of 0.4 SDS and 0.5 SDS below the UK
and US references, respectively. They had mean
BMI of 0.7 SDS and 0.9 SDS below both the
UK and US references, respectively.
Table 1. Details of 4350 study
Age (years)
Sex
Ethnic group
Affluence
Mean (SD): 9.9 (3.5)
Female: 2243, Male: 2107;
Total ¼ 4350
Igbo: 1099, Hausa/Fulani: 2232,
Yoruba: 1019
Fee-paying schools: 2195,
Government-funded schools: 2155
Fig. 1. Distribution of mean HAZs according to age and sex.
347
Figures 1 and 2 show the distribution of mean
HAZ and BMI Z score according to age and sex. In
multiple regression analysis, age, ethnicity and affluence were independent factors that significantly affected the HAZ scores (p < 0.01) and BMI Z scores
(p < 0.01). The distribution of mean height and
BMI for age Z scores are shown in Table 2.
PREVALENCE OF STUNTING,
UNDERWEIGHT AND OBESITY
The prevalence of stunting in SNC was 5.4% in girls
and 7.3% in boys (Table 3). Yoruba children had significantly higher rate compared the other groups
(p < 0.01). This appears to be owing to the significantly higher rate of stunting among Yoruba children
attending government-funded schools when compared with similar children in other ethnic groups
(p < 0.01).
The rate of obesity is low (1.4%) among Nigerian
children, with no significant difference between the
girls and boys (p ¼ 0.3). The rates of obesity were
significantly higher among affluent children (2.9% vs.
0%; p < 0.01) and younger children aged <11 years
(1.7% vs. 0.9%; p ¼ 0.03). Hausa children appeared
to exhibit the double burden of underweight and
obesity, with affluent Hausa children having the
highest rate of obesity (4.1%) and less affluent
Hausa children having the highest rates of underweight (26.6%). The differences between the ethnic
groups persisted when we adjusted for age, sex and
affluence.
348
Growth Characteristics of School-age Nigerian Children
Fig. 2. Distribution of mean BMI for age Z scores according to age and sex.
Table 2. The distribution of mean HAZ and mean BMI for age Z score
Age band
N
Mean
height
SD
Fee-paying private school boys
All ages
1057 138.6 18.1
Under 11 years
611 126.1 10.4
Over 11 years
446 155.6 11
Government-funded public school boys
All ages
1050 134.4 17.1
Under 11 years
575 122.1
9.3
Over 11 years
475 149.2 11.3
Fee-paying private school girls
All ages
1138 137.5 18.0
Under 11 years
677 125.4 12.3
Over 11 years
461 154.7
8.6
Government-funded public school girls
All ages
1105 135.1 15.9
Under 11 years
561 122
8.5
Over 11 years
544 148.2
9.4
Mean
BMI
SD
HAZ UK
1990
HAZ CDC
2000
BMI Z UK
BMI Z CDC
2000
16.5
15.7
17.5
3.1
3
2.8
0.1
0.1
0.6
0.2
0.1
0.7
0.6
0.5
0.7
0.7
0.6
0.9
15.5
14.5
16.6
2.0
1.5
1.9
0.9
0.6
1.2
0.9
0.6
1.2
1.2
1.3
1.0
1.3
1.5
1.2
16.9
15.3
19.1
3.6
2.5
3.7
0
0.2
0.3
0
0.2
0.3
0.5
0.6
0.3
0.5
0.7
0.4
15.8
14.3
17.4
2.6
1.7
2.5
0.8
0.4
1.2
0.8
0.4
1.2
1.1
1.4
0.9
1.2
1.5
0.8
DISCUSSION
Our study has characterized the growth pattern of
SNC from childhood to adolescence. Overall, SNC
are shorter than their UK and American counterparts.
The difference in height was more marked in boys,
older children, and those attending governmentfunded schools. The heights were similar at the start
of school age and then started to decline. The decline
in height appeared to peak at 15 years for boys and
13 years for girls. While the magnitude of the pubertal
growth spurt is diminished in cross-sectional data, the
timing is the same. The difference between the median heights for age showed that linear growth appeared to accelerate between the age of 13–14 years
in girls and 15–16 years in boys. Younger affluent
children attained similar heights to international references with mean HAZ score of 0.1. However, above
the age of 11 years, height begins to falter, as older affluent boys had a mean HAZ score of 0.6 while
older girls had mean HAZ score of 0.3.
Growth Characteristics of School-age Nigerian Children
349
Table 3. Prevalence of stunting, tall stature, underweight and obesity
Descriptor
All
Yoruba
Igbo
Hausa
Percent of children Percent of children
with stunting
with tall stature
(HAZ score <2)
(HAZ >2) (%)
(%)
All
Male
Female
Fee-paying private schools
Government-funded
public schools
All
Fee-paying private schools
Government-funded
public schools
All
Fee-paying private schools
Government-funded
public schools
All
Fee-paying private schools
Government-funded
public schools
Percent of children
underweight
(BMI Z score <2)
(%)
Percent of children
obese
(BMI Z score >2)
(%)
6.3
7.3
5.4
2.2
10.5
6.4
6.1
6.7
9.6
3.1
15.7
17.6
13.6
11.8
22.7
1.4
1.5
1.2
2.9
0
19.6
2.8
33.3
5.4
11.8
0.5
11.6
5.8
16.3
0.6
1.5
0
2.3
1
3.9
9
14.5
2
5.5
4.4
7
0.7
1.3
0
1.8
2.7
2.0
5.6
6.2
4.9
22.5
18.4
26.6
2
4.1
0
Ayoola et al. [11] showed that adolescent males
in rural southwestern Nigeria continued to be
shorter than African-American males up until the
late teens and into their early 20s. However, by
young adulthood, the entire deficit in height among
the females and much of that in the males had been
recovered. In her study, while heights of 2 SDS
occurred in > 60% of the boys and 35% of the girls
aged 13–14 years, <10% would be considered ‘short’
as young adults. The rate of stunting in Ayoola’s
study is much higher than in ours (possibly because
her study was limited to less affluent adolescents);
however, both studies find a similar pattern of decelerating growth in adolescence. One possible explanation for this growth pattern is constitutional delay
of growth and puberty. We did not formally assess
puberty (a limitation of our study); however, studies
from Benue [21] and southwestern Nigeria
[22]showed that the average age of menarche is
similar to international means. Our finding of relative
short stature compared with international references
(especially in the older, less affluent children) is
similar to findings in other developing countries
[23–27]. The etiology is unclear, but some authors
have suggested that poor nutrition and recurrent infections may be responsible, rather than differences
in genetic potential [24, 25]. While this may be the
case in children from less affluent backgrounds, it
does not explain the pattern of growth observed
among the affluent children studied here.
The rates of stunting for various ethnic groups in
our study varied from 19.6% for Yoruba children, 2.3%
for Igbo children and 1.8% for Hausa/Fulani children.
Although a large part of the disparity could be accounted for by differences in age and affluence, differences still persisted when these were corrected for. The
difference was more marked in Yoruba children attending government-funded schools, with a third of them
in our study being short. The effect of affluence on
growth may be largely owing to poor nutrition among
the less affluent, causing stunting. The rate of stunting
for Yoruba children in our study is similar to previous
reports: Senbanjo et al. [10] reported 17.4% among
Urban Yoruba children living in Abeokuta, while
350
Growth Characteristics of School-age Nigerian Children
Oninla et al. [9] reported 19.8% among urban school
children in Ile-Ife, Nigeria. Ukoli et al. [18] in 2003 reported that the prevalence of stunting in Igbo children
was 14.2% for the boys and 17.4% for the girls for Igbo
girls, while other studies, similar to ours, have not
shown any difference in height between Igbo children
and NCHS (National Center for Health Statistics) reference values for height[12, 17].
At all ages, sex and affluence, SNC were lighter
than international references. In all, 17.8% of boys
and 13.6% of girls were underweight. Affluent children who had similar heights to international references were lighter with a mean Z score of 0.7 for
boys and 0.5 for girls. This is unlikely to be because of poor nutrition but may reflect the relatively
lower energy density of Nigerian diets compared
with European and American diets.
Obesity was absent in the less affluent children in
all three ethnic groups. Hausa children appeared to
exhibit the double burden of underweight and obesity, with affluent Hausa children having the highest
rate of obesity (4.1%) and less affluent Hausa children having the highest rates of underweight
(26.6%). This pattern can lead to long-term sequelae
as undernutrition persisting through childhood may
have significant effects on cognitive development,
school achievement and later health [28], while
childhood obesity is associated with increased risk
of developing cardiovascular disease and Type 2
diabetes [29].
Our study has established that the growth patterns of SNC appear to be different from that of
international references, with affluent Nigerian children being lighter in weight and having a similar
height during childhood followed by a period of
decelerating growth. There is therefore the risk of
over-diagnosing short stature and underweight if
health workers continue to use growth charts derived
from other geographical areas. Our study also highlights the differences in rates of stunting, obesity and
underweight among the three ethnic groups, which
may reflect both disparities in socioeconomic status
as well as genetic traits.
ACKNOWLEDGEMENT
We acknowledge the help of Dr Andrew Blann in the statistical analysis of the data.
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