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* Post-Graduate Program in Epidemiology, Universidade Federal de Pelotas, CP 464, 96001-970, Pelotas, RS, Brazil and PAHO/WHO Latin-American Center for Perinatology and Human Development, Montevideo, Uruguay
2 To whom correspondence should be addressed. E-mail: denise{at}epidemio-ufpel.org.br.
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ABSTRACT |
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 TOP ABSTRACT SUBJECTS AND METHODSRESULTSDISCUSSIONLITERATURE CITED |
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0.2 cm in the adolescent's height (P = 0.001). The current findings reinforce the importance of early life factors in the determination of adult height.
KEY WORDS: • height • adolescence • cohort study
Adult height has been found to be inversely related to mortality, but this association is influenced by social background (1). Considering that the adult height attained is determined in part by factors acting during pregnancy, infancy, and childhood, the association between height and mortality is consistent with the effects of early life factors on morbidity and mortality in adulthood (2).
In a recent review, Silventoinen (3) wrote that in modern Western societies, 20% of the variation in adult body height was due to environmental factors, whereas in poorer environments, this proportion is probably larger, with socioeconomic factors playing a greater role. The most important nongenetic factors affecting growth and adult body height are nutrition and diseases. This review concluded that body height is a good indicator of childhood living conditions, not only in developing countries but also in modern Western societies.
Even though the influence of genetic factors on adult height is known, the secular trend toward increased height observed in many countries (4) was assumed to result from improvements in nutritional intakes and reductions in infectious disease in childhood (5). Studies across 2 generations in Guatemala showed that nutritional supplementation in childhood has positive effects on both the supplemented persons and their offspring (6).
Environmental factors, such as social class, parental education, maternal smoking during pregnancy, prenatal and postnatal growth have all been related to height (7–11). British birth cohorts studied biological and social determinants of adult height (10,11), whereas the Guatemalan longitudinal study (9) analyzed only biological factors (prenatal and postnatal components). Although environmental and social effects on size at birth and during childhood are well described (12–14) their influence on adult height is less clear. In addition, there is no study that examined both physiological and behavioral determinants of adult height in the developing world.
In Pelotas, a southern Brazilian city, a population-based birth cohort has been studied since 1982 (15). The association between anthropometric variables in early life and overweight in adolescence was investigated. Rapid growth in childhood was associated with increased prevalence of overweight in adolescence (16). In another analysis, teenage pregnancy was associated with shorter stature and higher BMI, after adjustment for previous anthropometric status, social, and biological characteristics (17).
The objective of this study was to investigate the influence of biological and social background variables on the height of 19-y-old adolescent girls. The explanatory variables under study included family income and maternal schooling indicating socioeconomic level; maternal height as an indicator of genetic potential; prenatal factors, i.e., birth weight, gestational age, maternal weight gain, and smoking during pregnancy; postnatal factors, including breast-feeding, nutritional status, and hospitalization at age 2 and 4 y; and age at menarche.
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SUBJECTS AND METHODS |
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TOPABSTRACTSUBJECTS AND METHODSRESULTSDISCUSSIONLITERATURE CITED |
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Height was measured using locally manufactured stadiometers, by trained interviewers who followed standardized techniques (20).
Data on explanatory variables were obtained in different phases of the study. Information collected in 1982 included socioeconomic variables (monthly family income in minimum wages and schooling of the adolescents' mother), maternal characteristics during pregnancy (weight gain and smoking defined as smoking at least 1 cigarette/d at any time during pregnancy) and characteristics at birth (age, height and pregestational weight of the adolescents' mother, gestational age, and birth weight). Information on breast-feeding and hospitalizations was obtained at the 1983, 1984, and 1986 follow-ups. The earliest available information was used in this analysis. Total breast-feeding time was reported in months and days. Starting in wk 1 of life, almost all children received herbal teas or water. Duration of predominant breast-feeding recorded the age at which foods other than breast milk or teas or water were introduced. Children were weighed using portable scales (CMS Weighing Equipment) and their supine length (1984) or height (1986) was measured using locally manufactured boards according to international specifications (AHRTAG). Nutritional indices were expressed as a Z-score of the NCHS reference (21). Children who presented weight for height index greater than +2 Z-score were classified as overweight. Height for age and weight for age deficits were defined by a Z-score below –2.
Age at menarche was obtained in 2001 by asking the adolescent. This information was also collected in early phases of the study for a subsample of girls. Comparisons between the 1997 and 2001 follow-ups showed excellent agreement between the 2 results. The variable was analyzed as continuous or dichotomous (<13 y vs. 
13 y).
ANOVA was used to compare means (F-test and linear trend for ordinal variable). Values are means ± SD. Linear regression was used in the crude and adjusted analyses. Multiple linear regression analysis of the determinants of attained height was carried out in accordance with a hierarchical conceptual model (Table 1), in which variables in the same level were adjusted for others or higher levels. This approach takes into account both the level of statistical significance (P < 0.2) as well as postulated hierarchical relations between the explanatory variables to identify potential confounders that required adjustment (22). The first level included socioeconomic variables (family income and maternal schooling); variables that had a P-value 
0.2 were included in the next level of the analysis. Biological maternal characteristics before pregnancy (age, weight, and height) were analyzed in the second level, whereas weight gain, smoking during pregnancy, and gestational age were in the third level. Birth weight and breast-feeding duration were included in the next 2 levels. Each one was adjusted for others in higher levels. The sixth and seventh levels included anthropometrical variables and hospitalization at age 2 and 4 y, respectively. Finally, age at menarche was included in the last level.
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The proposal was approved by the Ethical Research Committee of the Federal University of Pelotas. Written informed consent was obtained from all participants.
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RESULTS |
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TOPABSTRACTSUBJECTS AND METHODSRESULTSDISCUSSIONLITERATURE CITED |
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The crude results (Table 2) showed a positive linear association between socioeconomic variables and height at age 19 y. Girls who belonged to poor families and whose mothers were in the lowest schooling category were 4 cm shorter than girls from rich families whose mothers had 9 y of schooling. The height of the girls increased with increases in their mothers' age, pregestational weight, and height in 1982. Girls whose mothers had smoked during pregnancy were 2 cm shorter than the others. A positive linear association was also observed between maternal weight gain during pregnancy and height at age 19 y, but gestational age did not affect height (Table 2).
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4000 g were 9 cm taller than those who had a low birth weight (166.3 ± 6.1 and 157.2 ± 5.8, respectively; Table 3). Girls who were small for gestational age at birth were 5 cm shorter than all others. Height was not associated with either total or predominant breast-feeding.
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8 cm.
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DISCUSSION |
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TOPABSTRACTSUBJECTS AND METHODSRESULTSDISCUSSIONLITERATURE CITED |
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The secular trend in increased adult height was also observed in developing countries (6,24). In a prospective study, 267 children from 4 Guatemalan villages have been followed since 1969 (6). Birth weight, length at 15 d of age, and length at 2 y of age were positively associated with adult height, whereas ponderal index was not a significant predictor. Prenatal and postnatal growth were equally important determinants of height.
The literature shows that short stature in adults is associated with poorer educational status and lower socioeconomic level. This is due mainly to family background, but other environmental factors in childhood may also contribute to this association (3). The present study showed an association between socioeconomic background in childhood and height at age 19 y. In addition, the influence of maternal nutrition may represent a combination of genetic and socioenvironmental factors.
The most important nongenetic factors affecting growth and adult height are nutrition and disease. In our adjusted analyses, no association was observed between hospitalizations and height at age 19 y, but we did not have detailed information on disease episodes that did not lead to hospital admissions. Two other Brazilian studies showed that height decreased with hospitalization in childhood, but their outcome measure was height among children < 5 y old (25,26). It is possible that such an effect is no longer apparent in late adolescence.
Considering maternal height and birth weight, our results were similar to those of the 1958 British birth cohort (10), which found that parental height was positively associated with adult height in the offspring. In addition, midparental height captured the joint effects of both parents and had a stronger effect than that of either parent's height. Birth weight was also positively associated with adult height in the British cohort. Unlike in our study, the association between maternal smoking during pregnancy and height at 33 y of age disappeared after adjustment for parental height, birth weight, family size, and social class. However, the hierarchical conceptual approach used in our analyses (22,27) states that birth weight is not a true confounder of the association between smoking in pregnancy and height of the offspring; rather, it is a mediating factor. Therefore, adjusting for birth weight may lead to an underestimation of the true effect of maternal smoking. In the present study, the association between maternal smoking and height at age 19 y remained significantly associated after adjustment for family income, maternal age, weight, and height.
In the present study, breast-feeding was not associated with height at age 19 y, but the possibility of lack of power must be considered. Results of an analyses of a larger sample of 2250 adolescent men in our cohort showed that the association between total breast-feeding and height at age 18 y tended to be significant (P = 0.06), although the actual size of the effect was small (28). Longitudinal data from Israeli infants showed that despite their slower growth rate, breast-fed children reached the same final height and adult BMI as formula-fed children (29). In a 1958 British birth cohort, the effect of breast-feeding was substantially weakened in the adjusted analyses (10).
The 1958 British birth cohort showed that adult height, measured at 33 y, was accurately predicted by height measured at ages 7, 11, 16, and 33 y (30). Menarche also played a role. For example, girls with onset of menarche by age 11 y (1.62 m) were significantly shorter than those with onset after this age (1.63 m) in the 1958 British birth cohort. In the present study, height at age 19 y was 1.61 ± 0.06 m for girls with onset of menarche before age 13 y and 1.62 ± 0.06 m for those with later onset. In addition, after adjustment for confounding, the effect of age at menarche on height at age 19 y was stronger.
Our study had limitations. Losses during follow-up represented about one-third of all girls who should have been found in 2001. Analysis of the background characteristics of those who were lost to follow-up showed that there were no differences in maternal schooling, but losses were more common among girls who belonged to low-income families. Considering that adolescents from poor families were shorter, an increased effect of family income on height could be expected. On the other hand, the proportion of girls identified did not vary markedly according to birth weight. Therefore, it is unlikely that the association between birth weight and adult height is due to selection bias. Unfortunately, birth length was not collected by the study team and the first measure of length was not obtained until age 2 y. Although length at birth was not associated with BMI 20 y later in a cohort of Danish men (31), a positive association between birth length and adult height was stronger than between birth weight and adult weight in men from Norway (32).
Adult height has been positively associated with cancer risk (33), whereas an inverse association between height and cardiovascular disease was described (34). Genetic factors may be a plausible explanation; however, the associations maybe simply be a reflection of environmental factors affecting childhood growth and chronic disease. For instance, birth weight, infant feeding, diet, and parental smoking may influence both adult height and cardiovascular disease. In this study, maternal height was strongly associated with offspring height; however, environmental variables were also associated with adult height.
In conclusion, the main determinants of height at age 19 y in adolescent girls were family income, maternal pregestational weight, maternal height, smoking during pregnancy, birth weight, height gain, and age at menarche. These analyses showed that birth weight was a stronger predictor of height than weight gain during infancy taking into account negative effects of weight at ages 2 and 4 y when adjusted for birth weight. On the other hand, an adjusted effect of height at age 4 y on height at age 19 y suggests that height gain between 2 and 4 y is also important. Results from developed countries suggest that social inequalities in height are substantially reduced in subsequent generations, in parallel with economic development (35). These findings, as well as the present results, highlight the continued importance of socioeconomic and early life factors in promoting healthy long-term growth.
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FOOTNOTES |
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Manuscript received 26 June 2005. Initial review completed 2 August 2005. Revision accepted 17 November 2005.
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TOPABSTRACTSUBJECTS AND METHODSRESULTSDISCUSSIONLITERATURE CITED |
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