Research article Open Access
The Secular Growth Changes in Height and Weight of Mongolian Children over the Past 50 Years
Munkhzaya M1*, Undram L2, Ser-Od K3, Khuderchuluun N4, Chimedsuren O5 and Tsolmon C6
1Lecturer, Department of Occupational Health, School of Public Health, Mongolian National University of Medical Science, S.Zorigstreet –3, Ulaanbaatar, 14210, Mongolia
2Senior lecturer, Department of Health Policy, SPH, MNUMS, S. Zorigstreet –3, Ulaanbaatar, 14210, Mongolia
3Department of Epidemiology and Biostatistics, SHP, MNUMS, S. Zorigstreet –3, Ulaanbaatar, 14210, Mongolia
4Senior lecturer, Department of Epidemiology and Biostatistics, SHP, MNUMS, S. Zorigstreet –3, Ulaanbaatar, 14210, Mongolia
5Professor, Dean of SPH, MNUMS, S. Zorigstreet –3, Ulaanbaatar, 14210, Mongolia
6Professor, Department of Occupational Health, MNUMS, S. Zorigstreet –3, Ulaanbaatar, 14210, Mongolia
*Corresponding author: Munkhzaya M, Department of Occupational Health, School of Public Health, Mongolian National University of Medical Science, S.Zorigstreet –3, Ulaanbaatar, 14210, Mongolia, Tel: 976 95957982; Fax: 976 11 329126; E-mail: @
Received: December 26, 2017; Accepted: January 02, 2018; Published: January 22, 2018
Citation: Munkhzaya M, Undram L, Ser-Od K, et al. (2018) The Secular Growth Changes in Height and Weight of Mongolian Children over the Past 50 Years. Int J Marine Biol Res 3(1): 1-7. DOI: 10.15226/24754706/3/1/00118
Abstract
A little information regarding the changes in height and weight among children in Mongolia is available. The purpose of this paper is to report the secular growth changes in height and weight among schoolchildren in Ulaanbaatar city, Mongolia. The main purpose of the study was to determine the secular changes in height and weight of Mongolian children aged 8-17 years over the past 50 years. Height and weight were measured with Physician Beam Scale. Data analysis was made on SPSS-17.0 software. Arithmetical mean with standard deviation for each group (M ± SD) and standard error of the mean were calculated. In order to detect some changes in height and weight of children in different years, meta-analysis was performed (Cohen’s d). In 1962-2010, there was an statistically significant increase (p < 0.05) in average height of boys at the age of 8, 9 and 13-17 years old whereas there was a decrease of average height of boys aged 10, 11 and 12 years from 1978 to 1992, and 8-10, 14-17 years from 2010 to 2015. An increase in girls’ average height occurred throughout all age groups except decrease in girls’ height aged 10-12 years and 10, 12, 14-17 years in 1992-2010 and 2010-2015 respectively. There was a statistically significant increase (p < 0.05) in average weight for boys and girls throughout all age groups except decrease in weight of children’s of both sexes aged 12-17 years old in 2010-2015. In seven out of 10 age groups (8, 9, 10, 14, 15, 16, 17 years old) heights of boys were decreased with medium size effects in 2010-2015. The present study has shown that there were both upward and downward changes in height and weight of schoolchildren in Ulaanbaatar city during 1962-2015.

Keywords: Secular growth changes; Height; Weight; Effect size;
Introduction
The secular trend of growth compares changes in anthropometric parameters that occur from one generation compared to the previous one. Today, it’s considered that the term ‘secular trend’ – suggesting mainly an ascending trend – should be replaced by the secular growth change, as body size and maturation rate may grow, decline or remain unchanged [1]. With the trend related to height values, at certain ages there occur co-related changes in weight.

As we know, growth of all living being including the children here is determined by gene, though final expression is the summation of a complex interaction of some factors such as nutrition, socio-economic and geo-climatic, which ultimately modify the manifestation of genetic potential to higher and lesser intensity [2-7]. Some reports advocate well documented changes in weight especially, height among adolescents [8-12], but still other studies reported increase of height in a populations [8,13,14], with information of height leveling-off in children in Poland and Germany [15,16]. Information regarding the changes in height and weight among children in Mongolia is meagre. The purpose of this paper is to find out the secular growth changes in respect of height and weight among schoolchildren in Ulaanbaatar city, Mongolia.
Materials and Methods
The main purpose of the study was to determine the secular changes in height and weight of Mongolian children, in the age group of 8-17 years over the past 50 years. Therefore, 1962, 1978 and 1992 National growth charts data (space) on height and weight of schoolchildren were considered for comparative analysis. In 2010 and 2015, height and weight data of 2000 and 1600 schoolchildren, age group 8-17 years, were collected, respectively. In 2010 and 2015, participated children were enrolled from 13 schools of Ulaanbaatar city. Some 80-100 children from each age and sex were selected, the reason for this was to be able to compare with National charts data which were collected from around 100 children in UB each age and sex.

Height and weight were measured with Physician Beam Scale (Detecto 339 Balance Beam Scale with Height Rod). Height was measured to the nearest 0.5 cm as each subject stood erect, barefooted with the head held in Frankfort horizontal plane. Weight was measured to the nearest 0.1 kg with light clothing and barefooted.

Data analysis was made on SPSS-17.0 software. Arithmetical mean with standard deviation for each group (M ± SD) and standard error of the mean were calculated.

In order to detect the changes in height and weight of children in different years meta-analysis was performed. Particularly, the effect size (Cohen’s d – standardized differences of means) was calculated using the following equation [17]:
Effect size= | X 1 ¯ X 2 ¯ | Average SD  X 1 , X 2 MathType@MTEF@5@5@+= feaagGart1ev2aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr 4rNCHbGeaGqiVu0Je9sqqrpepC0xbbL8F4rqqrFfpeea0xe9Lq=Jc9 vqaqpepm0xbba9pwe9Q8fs0=yqaqpepae9pg0FirpepeKkFr0xfr=x fr=xb9adbaqaaeGaciGaaiaabeqaamaabaabaaGcbaGaamyraiaadA gacaWGMbGaamyzaiaadogacaWG0bGaaeiiaiaadohacaWGPbGaamOE aiaadwgacqGH9aqpdaWcaaqaaiaacYhadaqdaaqaaiaadIfadaWgaa WcbaGaaGymaaqabaaaaOGaeyOeI0Yaa0aaaeaacaWGybWaaSbaaSqa aiaaikdaaeqaaaaakiaacYhaaeaacaWGbbGaamODaiaadwgacaWGYb GaamyyaiaadEgacaWGLbGaaeiiaiaadofacaWGebGaaeiiaiaadIfa daWgaaWcbaGaaGymaaqabaGccaGGSaGaamiwamaaBaaaleaacaaIYa aabeaaaaaaaa@551C@
Where:
X 1 ¯ Average of group1 X 2 ¯ Average of group2 MathType@MTEF@5@5@+= feaagGart1ev2aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr 4rNCHbGeaGqiVu0Je9sqqrpepC0xbbL8F4rqqrFfpeea0xe9Lq=Jc9 vqaqpepm0xbba9pwe9Q8fs0=yqaqpepae9pg0FirpepeKkFr0xfr=x fr=xb9adbaqaaeGaciGaaiaabeqaamaabaabaaGceaqabeaadaqdaa qaaiaadIfadaWgaaWcbaGaaGymaaqabaaaaOGaeyOeI0Iaamyqaiaa dAhacaWGLbGaamOCaiaadggacaWGNbGaamyzaiaabccacaWGVbGaam OzaiaabccacaWGNbGaamOCaiaad+gacaWG1bGaamiCaiaaigdaaeaa daqdaaqaaiaadIfadaWgaaWcbaGaaGOmaaqabaaaaOGaeyOeI0Iaam yqaiaadAhacaWGLbGaamOCaiaadggacaWGNbGaamyzaiaabccacaWG VbGaamOzaiaabccacaWGNbGaamOCaiaad+gacaWG1bGaamiCaiaaik daaaaa@599E@
SD – Standard deviation

The interpretation of the effect sizes was done using (Table 1).

Cohen’s effect size was considered small where d ≥ 0.2, medium as d≥0.5 and large effect size where d ≥ 0.8.

An effect size is exactly equivalent to a ‘Z-score’ of a standard Normal distribution. For example, an effect size of 0.8 means that the score of the average height in the one group is 0.8 standard deviations above the average height in the second group, and hence exceeds the height measurements of 79% of the second group.
Table 1: Interpretations of Cohen’s d effect sizes

Effect size, d

Percentage of group Y who would be below average A in group X

Probability that person from group Y will be higher than A from group X, if both chosen at random (=CLES)

Effect size, d

Percentage of group X who would be below average A in group Y

Probability that person from group Y will be higher than A from group X, if both chosen at random (=CLES)

0

50%

0.5

0.7

76%

0.69

0.1

54%

0.53

0.8

79%

0.71

0.2

58%

0.56

0.9

82%

0.74

0.3

62%

0.58

1

84%

0.76

0.4

66%

0.61

1.2

88%

0.8

0.5

69%

0.64

1.4

92%

0.84

0.6

73%

0.66

1.6

95%

0.87

Results
Anthropological data covering height and weight and age group of 8-17 were recorded, irrespective of sex. The (Figures 1, 2, 3 and 4) show trends in height and weight in each age group of both sexes for investigated years. Starting with 10 years, the girls catch up boys at their height; in contrary the boys of age group 17 catch up girls at their height and become taller. Present day children are taller than the children of 50 years ago but children’s growth leveling-off in the last years, particularly starting from 13 years old (Figure 1, 2).

Dynamics for the body weight is nearly similar to the stature but gender differences occur earlier for weight. Peak weight boost comes around at the age of 13 to 14 years for girls and boys (Figure 3, 4).

In 1962-2010, there was an statistically significant increase (p < 0.05) in average height of boys at the age of 8, 9 and 13-17 years old whereas there was a decrease of average height of boys aged 10, 11 and 12 years from 1978 to 1992, and 8-10, 14-17 years from 2010 to 2015 (Table 2).

An increase in girls’ average height occurred throughout all age groups except decrease in girls ‘height aged 10-12 years and 10, 12, 14-17 years in 1992-2010 and 2010-2015 respectively (Table 2).

There was an statistically significant increase (p < 0.05) in average weight for boys and girls throughout all age groups except decrease in weight of children’s of both sexes aged 12-17 years old in 2010-2015 (Table 3).

When we compare the statistically significant changes in height and weight over the years in children both sexes using effect sizes, it was revealed that in 1962-1978, there were in general medium effect sizes (d=0.7) in boys’ height, which means height of boys increased in average of 4.1 cm. In 1978-1992, decrease in height was revealed in three age groups such as 10, 11 and12 years old with effect size as 0.4, 0.1 and 0.5, which means that 66%, 50% and 69% of boys of those age groups in 1992 were shorter of the same age average height boys in 1978. But in 1998-2010, increase in height was noted in all age groups, and Cohen’s d ranged from 0.3 to 1.3.

The striking results were observed when boy’s heights of 2010 and 2015 were compared. In seven out of 10 age groups (8, 9, 10, 14, 15, 16, 17 years old) heights of boys were decreased with medium size effects (Table 4).

Regarding girls’ height, the similar changes in effect sizes were observed (Table 4).
Figure 1: Growth increment in respect to height in boys (1962-2015)
Figure 2: Growth increment in respect to height in boys (1962-2015)
Figure 3: Growth increment in respect to height in boys (1962-2015)
Figure 4: Growth increment in respect to height in boys (1962-2015)
Table 2: Comparison of children’s height over last 50 years, cm

Years

1962

1978

1992

2010

2015

Age

Sex

Mean ± SD

Mean ± SD

Mean ± SD

Mean ± SD

Mean ± SD

8

Boys

119.6 ± 4.7

122.3 ± 5.1

123.0 ± 6.2

128.8 ± 6.0

127.4 ± 4.9*

Girls

118.6 ± 4.8

120.4 ± 5.4

123.0 ± 6.4

126.3 ± 4.5

126.6 ± 4.1

9

Boys

123.8 ± 5.3

126.7 ± 5.1

128.7 ± 5.6

135.4 ± 6.3

131.7 ± 4.6*

Girls

122.7 ± 5.0

125.4 ± 4.3

130.9 ± 4.9

132.1 ± 6.8

132.6 ± 4.9

10

Boys

127.6 ± 5.8

132.3 ± 3.9*

130.8 ± 4.2*

137.0 ± 5.6

134.0 ± 5.7*

Girls

126.3 ± 4.8

130.7 ± 6.7

133.0 ± 5.1

137.6 ± 6.96

137.6 ± 4.9

11

Boys

132.0 ± 5.4

134.9 ± 5.2

134.2 ± 6.1

139.1 ± 5.9

144.1 ± 7.5

Girls

133.1 ± 6.2

137.6 ± 5.3

142.2 ± 7.7

139.4 ± 5.2

142.5 ± 5.5

12

Boys

137.2 ± 7.0

141.0 ± 5.1*

137.7 ± 7.0*

146.1 ± 7.4

148.5 ± 7.0

Girls

138.1 ± 6.6

141.4 ± 5.7

148.0 ± 7.4

146.2 ± 6.2*

144.8 ± 6.7

13

Boys

141.3 ± 6.2

147.4 ± 8.6

148.8 ± 7.6

152.6 ± 7.9

155.0 ± 6.3

Girls

142.9 ± 5.2

147.3 ±  6.3

152.6 ± 7.9

150.4 ± 5.8

151.7 ± 6.1

14

Boys

146.7 ± 7.5

152.0 ±  6.5

154.2 ± 8.2

163.3 ± 7.7

157.0 ± 7.2*

Girls

147.2 ± 6.3

149.5 ± 3.4

156.1 ± 6.6

160.4 ± 5.1

153.8 ± 5.5

15

Boys

152.7 ± 7.5

158.1 ± 6.1

161.0 ± 7.2

165.2 ± 6.6

162.4 ± 6.8*

Girls

150.4 ± 5.6

152.2 ± 3.9

159.6 ± 5.8

160.8 ± 5.4

159.7 ± 4.0

16

Boys

158.2 ± 6.0

161.1 ± 6.9

167.8 ± 6.6

169.9 ± 6.4

168.3 ± 5.6*

Girls

152.1 ± 5.2

155.4 ± 2.4

161.1 ± 6.7

163.9 ± 5.7

160.0 ± 5.8

17

Boys

163.4 ± 6.3

0

169.7 ± 6.1

173.7 ± 5.4

170.4 ± 5.6

Girls

152.7 ± 5.0

0

162.0 ± 4.1

164.1 ± 5.8

163.5 ± 5.1

*p < 0.05
Table 3: Comparison of children’s weight over last 50 years, kg

Years

1962

1978

1992

2010

2015

Age

Sex

Mean ± SD

Mean ± SD

Mean ± SD

Mean ± SD

Mean ± SD

8

Boys

22.4 ± 2.4

22.6 ± 2.4

25.1 ± 3.6

27.7 ± 4.8

27.1 ± 4.6

Girls

21.6 ± 2.3

21.8 ± 2.5

22.8 ± 3.6

25.7 ± 3.8

25.9 ± 4.2

9

Boys

24.1 ± 2.6

24.5 ± 2.7

25.9 ± 2.6

28.6 ± 5.6

29.9 ± 4.1

Girls

23.4 ± 2.6

23.7 ± 2.4

24.6 ± 3.5

28.8 ± 5

29.3 ± 5.4

10

Boys

26.1 ± 3.2

27.9 ± 2.2

28.5 ± 3.5

29.4 ± 6.2

30.1 ± 5.4

Girls

25.1 ± 3.2

26.3 ± 3.6

28.3 ± 3.8

30.5 ± 5.3

31.7 ± 7.0

11

Boys

28.6 ± 3.4

28.9 ± 2.8

30.2 ± 4.8

32.8 ± 6.0

39.1 ± 6.1

Girls

29.4 ± 4.3

30.4 ± 4.3

33.8 ± 5.6

33.3 ± 5.5

34.4 ± 7.0

12

Boys

31.9 ± 3.6

32.1 ± 3.5

33.9 ± 4.0

39.9 ± 7.9

39.3 ± 6.5

Girls

32.1 ± 4.8

33.1 ± 3.9

37.9 ± 5.5

40.5 ± 7.4

42.0 ± 6.7

13

Boys

34.4 ± 4.7

36.9 ± 5.5

39.9 ± 6.8

45.1 ± 8.6

41.4 ± 4.2

Girls

37.7 ± 5.4

37.9 ± 5.4

41.41 ± 6.2

41.45 ± 7.4

43.2 ± 6.2

14

Boys

38.6 ± 5.6

40.6 ± 7.1

44.0 ± 5.8

52.2 ± 6.8

46.4 ± 3.9

Girls

40.7 ± 6.2

41.0 ± 5.1

45.0 ± 6.3

50.3 ± 6.0

45.4 ± 6.5

15

Boys

44.8 ± 7.2

44.9 ± 5.6

45.8 ± 6.9

53.4 ± 5.9

52.2 ± 8.1

Girls

44.9 ± 5.9

45.0 ± 4.4

47.8 ± 5.3

51.9 ± 8.2

50.3 ± 7.4

16

Boys

48.6 ± 6.3

49.4 ± 6.6

54.4 ± 6.7

56.8 ± 7.6

53.7 ± 6.7

Girls

47.7 ± 5.5

48.0 ± 2.9

51.1 ± 5.7

54.5 ± 6.1

51.1 ± 3.7

17

Boys

54.4 ± 6.3

0

58.3 ± 6.2

61.1 ± 8.3

56.7 ± 6.1

Girls

49.0 ± 5.5

0

54.2 ± 5.6

55.3 ± 5.7

52.5 ± 2.8

*p < 0.05
Table 4: Children’s height decrease and their effect sizes

Boys

2010

2015

2010/2015

Girls

2010

2015

2010/2015

Age, years

Average ± SD

Average ± SD

Average height difference

SD, Average

Effect size, d

Age, years

Average  ± SD

Average ± SD

Average height difference

SD, Average

Effect size, d

8

128.8 ± 6.0

127.4 ± 4.9

-1.4

5.5

-0.3

8

126.3 ± 4.5

126.6 ± 4.1

0.3

4.3

0.1

9

135.0 ± 6.3

131.7 ± 4.6

-3.7

5.5

-0.7

9

132.1 ± 6.8

132.6 ± 4.9

0.5

5.85

0.1

10

137 ± 5.6

134 ± 5.7

-3

5.5

-0.5

10

137.6 ± 7.0

137.6 ± 4.9

0

5.95

0

11

139.1 ± 5.9

144.1 ± 7.5

5

6.7

0.7

11

139.4 ± 5.2

142.5 ± 5.5

3.1

5.35

0.6

12

146.1 ± 7.4

148.5 ± 7.0

2.4

7.2

0.3

12

146.2 ± 6.2

144.8 ± 6.7

-1.4

6.45

-0.2

13

152.6 ± 7.9

155 ± 6.3

2.4

7.1

0.3

11

150.4 ± 5.8

151.7 ± 6.1

1.3

5.95

0.2

14

163.3 ± 7.7

157 ± 7.2

-6.3

7.5

-0.8

14

160.4 ± 5.1

153.8 ± 5.5

-6.6

5.3

-1.2

15

165.2 ± 6.6

162.4 ± 6.8

-2.8

6.7

-0.4

15

160.8 ± 5.4

159.7 ± 4.0

-1.1

4.7

-0.2

16

169.9 ± 6.4

168.3 ± 5.6

-1.6

6

-0.3

16

163.9 ± 5.7

160 ± 5.8

-3.9

5.75

-0.7

17

173.65 ± 5.4

170.4 ± 5.6

-3.25

5.5

-0.6

17

164.1 ± 5.8

163.5 ± 5.1

-0.6

5.45

-0.1

Decrease in children’s weight was observed between average weight in 2010 and 2015 for both sexes. In (Table 5), differences in average weight, average SD and their effect sizes are given.
Discussion
In the study the average height and weight of schoolchildren aged 8-17 years old were compared to reveal secular growth changes over 50 years period. A secular upward and downward change for height and weight of schoolchildren in Ulaanbaatar city Height and weight had upward changes in children of both sexes during 1962 to 2010, and then from 2010 to 2015, there were leveling-off height and weight in most age groups of schoolchildren. For instance, at age 11 years, girls/boys were on average 2.1 cm taller in 1962-2015 and respectively at age 11, 12, 13, 14 and 15 years girls/boys on average 0.5, 0.3, 0.5, 0.4 and 0.1 kg heavier in 1962-2015. The height and weight levelling-off effect was obvious in boys and girls between 2010-2015 in most age groups. In regard to the observed diminishment in height and weight of children it would be interesting to determine the status of the developmental tempo, measuring bone age and pubertal stage, in other worlds measuring the rate of children maturity (Cole, 2000).
Table 5: Children’s weight decrease and their effect sizes

Boys

2010

2015

2010/2015

Girls

2010

2015

2010/2015

Age, years

Average  ± SD

Average ± SD

Average height difference

SD, Average

Effect size, d

Age, years

Average ± SD

Average ± SD

Average height difference

SD, Average

Effect size, d

8

128.8 ± 6.0

127.4 ± 4.9

-1.4

5.5

-0.3

8

126.3 ± 4.5

126.6 ± 4.1

0.3

4.3

0.1

9

135.0 ± 6.3

131.7 ± 4.6

-3.7

5.5

-0.7

9

132.1 ± 6.8

132.6 ± 4.9

0.5

5.85

0.1

10

137 ± 5.6

134 ± 5.7

-3

5.5

-0.5

10

137.6 ± 7.0

137.6 ± 4.9

0

5.95

0

11

139.1 ± 5.9

144.1 ± 7.5

5

6.7

0.7

11

139.4 ± 5.2

142.5 ± 5.5

3.1

5.35

0.6

12

146.1 ± 7.4

148.5 ± 7.0

2.4

7.2

0.3

12

146.2 ± 6.2

144.8 ± 6.7

-1.4

6.45

-0.2

13

152.6 ± 7.9

155 ± 6.3

2.4

7.1

0.3

11

150.4 ± 5.8

151.7 ± 6.1

1.3

5.95

0.2

14

163.3 ± 7.7

157 ± 7.2

-6.3

7.5

-0.8

14

160.4 ± 5.1

153.8 ± 5.5

-6.6

5.3

-1.2

15

165.2 ± 6.6

162.4 ± 6.8

-2.8

6.7

-0.4

15

160.8 ± 5.4

159.7 ± 4.0

-1.1

4.7

-0.2

16

169.9 ± 6.4

168.3 ± 5.6

-1.6

6

-0.3

16

163.9 ± 5.7

160 ± 5.8

-3.9

5.75

-0.7

17

173.65 ± 5.4

170.4 ± 5.6

-3.25

5.5

-0.6

17

164.1 ± 5.8

163.5 ± 5.1

-0.6

5.45

-0.1

Our findings of the leveling-off of the average height in school children is consistent with the study carried out by Uuganbayar et al that there was a diminished both height and weight trends between 2003 and 2014. They were looking at cardiovascular function of children in relation with physical development, and measured height and weight of schoolchildren. At this study there was a significant decrease in height in children of both sexes in the period between 2003 and 2014 [18]. A secular increase has been noted in some countries [19-22] although some countries reported on stabilization [14,15] and downward change in height and weight [23]. The results of these studies do not necessarily match in all details because of the different geographical regions, different socio-economic situations, different age groups, and different sample sizes and so on, but the general conclusion appears to be consistent.

In conclusion, the present study has shown that there were both upward and downward changes in height and weight of schoolchildren in Ulaanbaatar city during 1962-2015. An upward change in height and weight were during period of 1962-2010, and then in 2010-2015 downward change was observed in most age groups. Future study is aimed to determine if these secular changes are continuing and to examine possible explanations for and consequences of these changes.
Acknowledgement
We thank school children and teachers of those schools in Ulaanbaatar city who cooperated with this study.
Declarations
The Ethics Committee of the Mongolian National University of Medical Sciences approved the study in June 2015.
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