The impact of socioeconomic status on growth duri

　　　　 作者：Aly A ElNofely， Sahar A ElMasry

【摘要】 Objective: To explore the relationship between socioeconomic status from one side and physical growth and nutritional status from the other side， in infants versus adolescents in Egyptians.Methods: Three samples were investigated: a) A sample of 605 infants aged 6 months+1 week (287 girls and 318 boys). b) A sample of 992 infants of age 4～24 months (465 girls and 527 boys). c) A sample of 1864 children and adolescents aged 6～14 years of (744 girls and 1120 boys). All samples are from Big Cairo area of both urban and rural localities and of various socioeconomic strata. Body weight and length/ height had been measured and body mass index (BMI) had been calculated for every subject. Assessment of the impact of parental education level， locality and number of sibs， on growth and nutrition as indicated by BMI was attempted.Results: a) Breastfed infants (6 months +1 week) grow bigger in low socioeconomic strata and in rural areas than artificially fed infants. The practice of breast feeding was more common and lasted longer in low socioeconomic stratum than in middle and high one. b) A significant positive association between body mass index of infants (4～24 months) and the socioeconomic status (particularly level of father education reflecting family income) was proved. c) The socioeconomic factors had insignificant influence on BMI of school children aged 6～9 years， but it showed significant influence in the period 10 ～ 14 years. After the age of 9 years， children started the pubertal stage earlier and had higher BMI in the high socioeconomic strata as compared to those of low socioeconomic strata. d) In the low socioeconomic status， breast feeding compensates the deleterious influences of the environment on growth and physique of infants.Conclusion: children of educated parents have significantly low number of siblings' size in comparison to those of uneducated parents. Also children of educated parents are significantly more in number in urban areas than in rural areas， and vice versa. The interdependence between parental education and locality shows the highest level of significance in both sexes and at all ages.

【关键词】 Socioeconomic status; Nutritional status; Infant; Adolescent

　　 INTRODUCTION

　　The health condition， nutritional status and physical growth of children are three aspects of one biological entity reflecting the socioeconomic status in a community. The socioeconomic status is a term describing a complex phenomenon predicted by a broad spectrum of variables. It is often conceptualized as a combination of financial， educational and occupational influences[1，2]. These influences are， usually， interrelated; it has been proposed that each reflect somewhat different forces affecting nutrition， health and disease. However， the education level of the parents for example， could be recalled and recorded， in the feild with higher degree of accuracy than other variables. It indicates as well skills and concepts that could provoke acquisition of positive social， psychological and economic resources[3].

　　Infancy is a period of special significance being that of the most rapid growth velocity during human postnatal life. The brain weight doubles and body weight triples during the first year of life[1，4]

　　Puberty ， as well， is a special period with an obvious growth spurt which varies， among populations， in amount， age of take off， duration and age at peak height velocity， depending on numerous factors of which the socioeconomic environment is significant[5，6].Optimal feeding practice， provision of enough good building material and proper health care measures are essential for all the ongoing and future biological processes especially during infancy[7-12]. Commonly， poor hygienic conditions， high frequency of infections， poor family nutrition， short birth intervals and inadequate prenatal care are more often confound in low socioeconomic strata and in rural areas; particularly in developing countries. In these strata breast feeding is considered the primary infant feeding practice; besides， it is supported by the religious belief in some countries[13]. The mother is the backbone of the process of infant feeding， and her role in the success of breast feeding is essential， however， several factors appear to influence this role including her biological and social status as well as her knowledge and attitude towards infant feeding[14].

　　There are debates in the literature concerning the impact that the type of feeding， socioeconomic status and their interaction have on the infant's growth and nutritional status as indicated by body weight， body length and body mass index (BMI). Some authors demonstrated differences in some of these criteria as related to various feeding practices[7-10] others denied such differences[15-17]. However， the evident rise in BMI of infants during the last decade in some developed countries[18]still stressed the vital importance of environmental conditions on the BMI as indicator of the nutritional status.

　　Currently， BMI is one of the most acceptable indicators of the nutritional status of children particularly during the prepubertal period. It is associated with food intake， energy expenditure and both actual and perceived health status[19]， all are reflection of the socioeconomic status in the family.

　　The aim of this study is to explore the relationship between socioeconomic status from one side and physical growth and nutritional status from the other side， in infants versus adolescents in Egypt.

　　MATERIALS AND METHODS

　　The first sample included 605 healthy Egyptian infants of both sexes， aged 6 months+1 week， representing both urban (304 infants: 159 males and 145 females) and rural (301 infants: 159 males and 142 females) areas in Giza Governorate， Egypt. The age of six months was selected in order to facilitate collection of a sizable sample， since at this age infants are usually vaccinated against numerous diseases according to local health regulations. They were drawn from infants attending two different vaccination centers in each area. The selection of the sample was based mainly on the age of the infant， his health condition， and the locality. The sample was grouped according to sex and locality into 4 categories: urban males， urban females， rural males and rural females. Each sexlocality group was reclassified according to type of infant feeding during the first 4 months of age (as determined retrospectively according to nutritional history).The feeding groups were: exclusive breastfed infants (B.F.)， exclusive artificialfed infants (A.F.) and Mixedfed infants (M.F.). Then， the urban and rural subsamples are classified separately into 2 different socioeconomic strata， using the combined level of education score of both the father and mother， as we considered it the most reliable criterion. These social classes were high and low social classes. Distribution of the sample according to locality， type of feeding and socioeconomic strata is presented in table 1. We tested the significance of differences in infant's body weight and length (F ratio) according to socioeconomic status， locality and type of infant feeding; for total males， total females， and subgroups (urban males， urban females， rural males， and rural females).

　　Aly A ElNofely， et al.The impact of socioeconomic status on growth Table 1 Distribution of infants of first sample (aged 6 months) by type of feeding， socioeconomic status， sex and locality

　　The second sample consists of 992 healthy Egyptian infants of both sexes， aged 4～24 months. The study was conducted in Baby && Mother Health Care Centers of Cairo where various socioeconomic strata from different geographic localities were recruited. Education level of a parent was graded as: high for more than 12 years of regular education， middle for 6～12 years and low for less than 6 years. Then the sample was grouped into three socioeconomic classes depending on the combined level of education of both parents and number of persons per room (Education level of father× Education level of mother/ Number of persons per room) as: low， middle and high. Interaction of the BMI with the socioeconomic class was investigated. Table 2 represents the distribution of this sample by sex， parental level of education and socioeconomic class.

　　The third sample comprises 1 864 children (1 120 boys and 744 girls)， with age ranges between 5.5 to 14.5 years. Some of those subjects were collected from schools and social sporting clubs in Cairo representing urban area， others from schools of a neighboring rural area (AbuElNomros) in Giza representing rural area. The sample was classified according to the level of combined education of both parents; only the data of children whose parents are both educated (completed at least nine years basic compulsory education period in Egypt) or both uneducated have been included in this study. The number of siblings was considered high if it is equal to or higher than 4， and low if less.

　　Age of the subjects under study was calculated on basis of birth certificate. Based on a detailed questionnaire from the mother and a thorough clinical examination， infants and children included in the study were full term， with limited deviation in birthweight as reported by the mother or the family doctor， and free from chronic diseases or congenital anomalies. Then， the following anthropometric measurements were taken : body weight (Wt.) using portable lever scales accurate to 10 gm. For infants and to 100 g. for children， and body length (L.) for infants using Holtain infantometer (supinelength table)，and body height for children using Holtain Steel Bar anthropometer accurate to 1 mm[20]. The BMI was calculated as weight (kg)/ length (m2). Interaction of the infant's anthropometry with the socioeconomic factors (parental education， no. of siblings and locality) were investigated.RESULTS

　　As seen in Figure 1， the rate of exclusive B.F. at birth was higher (94.7%) in the rural area than in the urban area (89.8%)， and the duration was longer. Rural women continued exclusive B.F. for 4 months of age (63.5% males and 66.2% females)， approximately 21% of women continued B.F. for 6 months (18.2% males， 23.9% females). Among the urban mothers， breast feeding rates at 4 months of age were 43.0% (45.3% males and 40.7% females)and 10.2 % at 6 months of age (10.7% males ，9.7% females ) respectively. It is evident in table (1) that there were few (&<10%) artificially fed infants in the sample regardless of locality. In the rural areas， the majority of the infants (91.4%) were in low social class， and only 8.6% were related to the high social class. However， in the urban areas， 52.3 % were in low social class， and 47.7% were related to the high social class. After classification of infants into different types of feeding， it was detected that the majority of breastfed infants was related to low social class (80.7%)， and the minority was related to the high social class (19.3%). No significant differences in anthropometric measures were found between social classes， except for length in case of a combined sample of males and urban males， where high social class had higher value than low class of mean length (P&<0.05).

　　Figure 1 Percentage distribution of exclusively B.F. infants.Testing the interaction between infant's anthropometry and different types of infant feeding (Table 3 and 4)revealed that BF rural males have significantly the highest mean values for weight， and BF rural females have significantly the highest mean values for weight and length. In the urban area， anthropometrical measurements did not differ significantly according to feeding regimen.　Table 3 Test of the influence of type of infant feeding on body weight by sex and locality(Mean±SD).

　　In Egyptian infants aged 424 months (992 infants)， the degree of association between the education level of father and that of mother is highly significant (Table 6). Only about 5% of the couples were a highly educated father with poorly educated mother， but 73% were of similar education level. Table 5 demonstrates the variation of BMI by age and sex. BMI was neither steady nor identical in both sexes. Males always had higher BMI than females; however the differences are significant only for total sample and at the age of 18 months. Chisquare test revealed that father's education had no significant effect on the infant's type of feeding during the first 4 months of life; however mother s level of education is just significant at the 0.05 degree of probability. About 86% poorly of educated mothers breastfed their infants while 78% of highly educated mothers did the same. However， table 6 show significant impact of the SE level of the family on the BMI of Cairo infants. The level of father's education alone ( as it reflect family income) had significant influence as well， while mother's education had no significant influences on her infants BMI .Table 5 Body mass index for infants aged 4 to 24 months by age and sex.

　　In Egyptian children (6～14 years) from the large Cairo area (1 919 children)， BMI is constant at the early primary schoolage period (6～8 years)， and similar for both sexes (Table 6). Table 6 also represents the distribution of this sample in relation to the parental level of education， number of siblings and locality by sex and age.However， evident continuous increase in this index by age and for both sexes show up later (9～14 years) during the pubertal period. The increase is accentuated at the age of 12 years for girls， and 13 years for boys. The value of this index for girls exceeds those for boys for the last 3 age groups (12～14 years). In table 8 the results of the Chisquare test for differences in the distribution of the BMI by parental education， number of siblings and locality are presented. In males there is no significant dependence of BMI on parental education， number of siblings or locality till the age of 10 years. By the age of 11 years a significant influence of the three sociodemographic factors on BMI booms， and that influence continue， though with a lower level of significance， till the end of the age range studied. Combining all the male subjects together as one group， and testing the influence of each of the three sociodemographic factors on BMI， the results show a highly significant influence. These results indicated that boys of educated parents， with low no. of siblings and living in urban area， have significantly high BMI at the age period 11～14 years， but earlier (6～10 years)， the influence of these factors are insignificant. In females (Table 7) the general picture is similar to that in males， but with some differences: the Chisquare shoots up at the age of 10 years; i.e. one year earlier than males; and the significant influence disappear at age 14 years. The interaction between the 3 sociodemographic factors studied have been tested using the Chisquare test (Table 9)， and it has been proved that the 3 factors are significantly tied with each other at all ages for both sexes. In other words， children of educated parents have significantly low number of siblings' size in comparison to those of uneducated parents. Also children of educated parents are significantly more in number in urban areas than in rural areas， and vice versa. The interdependence between parental education and locality shows the highest level of significance in both sexes and at all ages.Table 7 Body mass index by age and sex in Egyptian children aged 6～14 years.　Table 8 Chisquare test for differences in distribution of body mass index by education of parents， number of siblings and locality for Egyptian children aged 6 to 14 years by sex and age.Table 9 Chisquare for interaction between the education of parents， number of siblings and locality for Egyptian children by sex and age.

　　DISCUSSION

　　There is increasing evidence about the significant impact of social factors on human growth and nutritional status， particularly in developing countries， where the potential for change is still high. This impact is not equal at all ages[21]. The perinatal and the adolescent periods are the growth periods most sensitive to environmental stresses. Perhaps this is because of the high speed of events and the marked growth and maturational changes during these two periods， hence any interruption will be far reaching. However females may be less sensitive than males to differences in environmental factors[22]. Some authors have even claimed that females may be physiologically buffered from environmental stress[23]. A look to the differences in secular trend in low and high social strata in a community and for a definite period reveals more secular trend in the lower social strata than the higher[24，25]. One could expect that increase in height and weight and acceleration in maturation can't continue for ever， but it might continue so far as environmental stresses are acting on the genetic potential of the character studied.

　　There is much debate， however， concerning the impact that type of feeding during the early months of life has on infant's growth and physique. Whitehead et al[7，10，26，27]reported that the growth of breastfed infants was superior to that of bottlefed infants. While other studies reported that growth of breastfed infants was inferior to the growth of formula fed infants in developed countries[4，8，28-30]. These authors， however， attributed their results partly to caloric excess. A third group of authors reported no differences between breastfed and formulafed infants in their studies[9，15-17，31，32] . According to Duncan et al and Dewey et al[33-35]， these contradictions are probably， partly due to methodological limitation i.e. criteria for classification and duration of type of feeding were not similar in these studies， and partly to different environments. The progressive decline in breast feeding in the urban area more than in the rural area was observed in numerous studies[36]. Usually mothers in rural areas spend longer periods with their children and live closely with their parents and other relatives who support B.F.[4].

　　The present study demonstrated evident differences between rural and urban infants as regard distribution of socioeconomic status as well as distribution of types of feeding during the first 4 months of life. Artificiallyfed maleinfants in the urban area tended to have slightly greater values in body weight and body length than breastfed and mixedfed infants. Probably urban mothers have better knowledge and practice about artificial feeding， i.e. ideal food which can be introduced， adequate concentration of formulamilk， sanitary habits in preparation of formulafeeding...etc. In contrast， breastfed infants (6months+1 week) grow bigger in low socioeconomic strata and in rural areas than artificially fed infants. The practice of breast feeding was more common and lasted longer in low socioeconomic stratum than in middle and high one. The higher the socioeconomic level， the higher the percentage of artificial fed infants. In certain communities， breast feeding is the primary feeding practice particularly if augmented by religious belief. Probably， this explains the small number of artificiallyfed infants in rural areas. Commonly， poor general hygiene， increased frequency of infections， poor nutrition， short birth interval and inadequate prenatal care are more confound in the rural area[37，38]. We believe that these factors interfere with the optimal growth of mixedfed and artificiallyfed infants， but had lesser effect on breastfed infants. It is the interaction of poverty and illiteracy with artificial feeding that could disturb infant's physical growth.

　　Education level of father， however， influences the BMI of infants aged 4 to 24 months significantly; the higher the education level the higher the BMI. The education level of the mother had no significant influences on her infant BMI. These results indicate higher impact of father's education on the socioeconomic status of the family in general and BMI of infants in particular. The variation of BMI by age might suggest differences between weight gains as compared to the gain in length at certain age periods.

　　In Egyptian children (6～14 years) from the large Cairo area， BMI is constant at the early primary schoolage period (6～8 years)， and similar for both sexes. However， evident continuous increase in this index by age and for both sexes show up later (9～14 years) during the pubertal period. Sociodemographic factors studied have significant influence on the timing of onset of pubertal spurt， i.e. children of educated parents， with low no. of siblings and living in urban area get through the pubertal spurt earlier than others， and have significantly high BMI at the age period 11～14 years， but earlier (6～10years)， the influence of these factors are insignificant. This influence becomes strongly significant at age10 to 12 years in girls and at age 11 to 14 years in boys. This most probably related to sufficient and more balanced feeding in addition to more facilities for health care for the privileged children during infancy and childhood. Later， less food per capita in quantity and quality， in large uneducated and rural families may be partially compensated in quantity by increasing the intake of cheap food leading to increased degree of adiposity[39]. Hence， differences in BMI between the two social groups may disappear at the late adolescence period and in adulthood particularly in females.

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