Leg and trunk length at 43 years in relation to childhood health, diet and family circumstances; evidence from the 1946 national birth cohort

MEJ Wadswortha, RJ Hardya, AA Paulb, SF Marshalla and TJ Colec

a MRC National Survey of Health & Development, Royal Free & University College Medical School, London WC1E 6BT, UK.
b MRC Human Nutrition Research, Elsie Widdowson Laboratory, Fulbourn Road, Cambridge CB1 9NL, UK.
c Department of Paediatric Epidemiology & Biostatistics, Institute of Child Health, University College London, 30 Guilford St, London WC1N 1EH, UK.

Professor Michael Wadsworth, MRC National Survey of Health & Development, Royal Free & University College Medical School, Department of Epidemiology & Public Health, 1–19 Torrington Place, London WC1E 6BT, UK. E-mail: m.wadsworth{at}ucl.ac.uk

Abstract

Background This is a study of the associations of adult leg and trunk length with early life height and weight, diet, socioeconomic circumstances, and health, and parental height, divorce and death.

Method The data used were collected in a longitudinal study of the health, development and ageing of a British national birth cohort (N = 2879 in this analysis) studied since birth in 1946. Multiple regression models were used to investigate the relationships.

Results Adult leg and trunk length were each positively associated with parental height, birthweight, and weight at 4 years. Leg length was associated positively with breastfeeding and energy intake at 4 years. Trunk length was associated negatively with serious illness in childhood and possibly also parental divorce, but not with the dietary data.

Conclusion Adult leg length is particularly sensitive to environmental factors and diet in early childhood because that is the period of most rapid leg growth. Trunk growth is faster than leg growth after infancy and before puberty, and may be associated with the effects of serious illness and parental separation because of the child's growing sensitivity to stressful circumstances, as well as the result of the biological effects of illness.

Keywords Leg length, trunk length, child health, diet

Accepted 8 November 2001

Short adult height is known to be a risk for cardiovascular and cancer mortality and for poor adult health,1–3 and leg length in childhood is also a marker of risk for cardiovascular disease and cancer.4–6

Greatest leg or lower body length is associated with advantaged socioeconomic circumstances in childhood,7–10 and environmental advantage in the preschool period in particular is associated with growth.11 Leg growth contributes markedly to stature attainment,12 and increased leg length was the major component of the secular trend in height increase in populations in Japan and Norway.13,14

Childhood height growth is associated also with prenatal growth,15 parental height,16 the child's health,16,17 history of emotional disturbance,18,19 and nutrition.10,20

This study asks whether the childhood health and environmental effects known to be associated with growth have different impacts on adult leg and trunk length, in order to further understanding of the observed associations of height with disease. Information used is from a national longitudinal study from birth to adulthood.

Method

Population
The Medical Research Council (MRC) National Survey of Health & Development is a social class stratified sample of 5362 of all the single, legitimate births that occurred in England, Wales and Scotland, 3–9 March 1946. That population has been studied on 21 occasions between birth and age 53 years.21,22 By age 43 years when outcomes reported here were made, permanent losses comprised 365 (6.8%) deaths, and 540 (10.1%) refusals, and temporary losses were 607 (11.3%) emigrations or residence overseas and 370 (6.9%) failures to contact. The population visited at 43 years (N = 3262) tended to under-represent the never married, the least literate, those always in manual social class circumstances, and the mentally ill.22 Those with physical illness were well represented.22 Losses through death were greater in the manual social classes than in the non-manual.23

Measures
Anthropometry
Outcome measures were adult leg and trunk length, derived from standing and sitting heights measured by a research nurse at a home visit when study members were aged 43 years. Leg length was calculated as the difference between standing and sitting heights, and trunk length was represented by sitting height. Standing height was measured to the nearest 0.5 cm using a lockable tape with foot plate, head piece and spirit level, with the head in the Frankfort plane position. This stadiometer was manufactured for the study by CMS Measuring Equipment (London). Sitting height was measured with the subject sitting upright on the base plate, which was on a flat seat, and with the head in the Frankfort plane position, feet on the floor, and the thighs unsupported.24

Birthweight was used to indicate prenatal development, and was recorded by midwives or obstetricians at birth, or taken from records by health visitors. Heights and weights at 4, 7, 11 and 15 years were measured at clinics by health visitors using their clinic's equipment and the study's protocol.25

Parental heights were included as markers of genetic influence. Mother's heights were measured by health visitors, at clinics using their own protocols, when their study child was aged 6 years, and mothers reported father's height.

Nutrition
Information on exclusive breastfeeding was obtained from mother's reports to health visitors when children were aged 2 years, and used here as ever/never breastfed, since breastfeeding was not associated in a dose-related fashion with either outcome. Health visitors asked, when study children were aged 4 years, ‘What did this child have for each meal yesterday?' This was coded in terms of foods and nutrient content.26 Energy was calculated in kilojoules. Some micronutrients have a role in bone matrix and connective tissue formation, and some may have specific effects on long bone growth,27,28 whilst others are markers of diet quality. As such, estimated mean daily intakes of energy, protein, calcium, phosphorus, magnesium, zinc, iron, vitamins A, C, and E, thiamin, riboflavin and niacin were included in this analysis.

Health in childhood
Mothers reported the child's illnesses to health visitors. This analysis included only serious illness, defined as lasting longer than 3 months in any one year or necessitating a continuous hospitalization of one month or more between birth and age 59 months. Reports of admissions were checked with hospital records.23

Socioeconomic circumstances in childhood
Father's occupation when the child was aged 4 years was coded using the Classification of Occupations29 (categorized into manual and non-manual). Crowding was coded in terms of people per room and categorized as overcrowded (>=2 people per room) or not (<2 people per room).

Emotional upheaval in childhood
Health visitors recorded custodial parents' reports of any parental separation as having occurred or not before the child's sixth birthday, and of parental death by the same age. This age was chosen to be consistent with that available for childhood illness.

Analysis
Leg and trunk length were sex standardized, by converting to internally derived standard deviation scores (z scores). A third outcome measure, defined as the difference in z score for leg length and z score for trunk length, was also considered, as a measure of disproportion, in order to test whether there were differential influences on leg and trunk length.

Unadjusted relationships between each of the independent variables and the three outcomes were tested using linear regression models. Where appropriate measures were entered as continuous variables and tested for linearity. Each nutrient was adjusted for energy intake at age 4 years. All nutrients, energy intake and weight at 4 years were logged using natural logarithms to reduce skewness, and multiplied by 100 so that the regression coefficients could be interpreted as the change in outcome per one per cent in the variable.30 Since there were no statistically significant sex by risk factor interactions (P > 0.05 in all cases), all models included data from both sexes. These analyses were restricted to those who had been contacted at 4 years of age.

All factors associated in the initial analyses (with a P-value <0.1) with an outcome were considered for inclusion in the multiple regression models for that outcome. Where there was clear confounding only the stronger factor was included in the multiple regression model. These models were then adjusted for both weight and height at 4 years of age. That age was chosen because diet information was collected then, and because it represented a stage of early life growth that is well differentiated from prenatal growth. Height at 4 years was then replaced by height at ages 7, 11 and 15 years in turn in order to investigate the stage of growth during which the early life factors were influential. If any height measure cancelled out the effect of an early life factor then it may be assumed that the effect of that factor is accounted for, because its influence is seen already in terms of height.

Analyses were performed using the computer software Statistical Package for the Social Sciences.31

Results

Mean leg length at 43 years was greater in men (83.3 cm, SD 4.99) than in women (75.6 cm, SD 4.72). Description of the explanatory variables is provided in Table 1Go. The correlation between trunk and leg length z scores was low at 0.1. The difference was strongly correlated with both components of height (0.7 for leg length and –0.7 for trunk length). The unadjusted relationships of leg and trunk length with each of the dependent variables are shown in Table 2Go. Leg length and trunk length were positively associated with mother's and father's height, with the effect being greater for leg length. The associations between father's height and leg and trunk length were curvilinear, with the positive effect becoming greater with increasing paternal height (P < 0.01 for a quadratic trend in both cases). Birthweight was positively associated with both components of height. Those from a non-manual social class had greater mean leg and trunk length than those from a manual social class, and this association was stronger for leg length. Leg length and trunk length were shorter in those not breastfed and when home circumstances were crowded, with the effects being considerably stronger for leg length. Energy intake was associated with leg and trunk length, the effect being stronger for leg length. After adjustment for energy intake, leg length was associated positively with intakes of all nutrients and particularly with vitamins A and C and with riboflavin and niacin, and trunk length was positively associated with intakes of vitamins C and E. Trunk and leg length were each shorter in those who experienced serious illness with the effect being greater for trunk length. Trunk length but not leg length was also shorter in those who experienced parental divorce.


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Table 1 Descriptive statistics for the explanatory variables
 

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Table 2 Regression coefficients for the unadjusted effects of each variable on leg length, trunk length and the difference between leg and trunk length
 
Mutiple regression analysis of leg length
After further adjustment of each nutrient that showed a significant relationship with leg length (in Table 2Go) for parental height, birthweight, father's social class, crowding, breastfeeding and serious childhood illness, none remained significant. All coefficients were reduced (vitamin A and vitamin C to 0.0005, riboflavin to 0.0003 and niacin to 0.09). Energy intake was considered for further analysis rather than the individual nutrients. Father's social class, crowding and parental heights accounted for this weakening of the effects, and so it is likely that the nutrients were a proxy for socioeconomic circumstances. Crowding and father's social class were confounded, since the effect of each was considerably weakened when included in a model together with neither remaining significant at the 5% level. Social class was selected for further analysis, as the stronger factor.

The independent relationship of leg length with nutrition, in the form of breastfeeding and energy intake, was confirmed in a multiple regression model (Table 3Go, column 2). The breast fed had an estimated leg length 0.13 standard deviations greater than others, while an increase of one per cent in energy intake was associated with an increase of 0.0025 standard deviations in leg length. Parental heights, birthweight and weight at 4 years were also associated independently with leg length (Table 3Go, column 2). Father's social class was to some extent confounded with mother's height and father's height. After adjustment for height and weight at age 4 years, the effect of father's social class was weakened and was no longer significant (Table 3Go, column 3). Height at 4 years accounted for some, but not all, of the effects of breastfeeding and energy intake. The effect of birthweight also became weaker, but remained significant (P = 0.04). The initially weak influence of childhood serious illness got even smaller with each stage of adjustment. Height and weight at 4 years were strongly positively associated with leg length.


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Table 3 Regression coefficients for the final model for leg length (unadjusted and adjusted coefficients given for the same sample for comparison)
 
All later childhood heights were positively associated with leg length. Height at 7, 11 and 15 years greatly weakened the effects of breastfeeding, energy intake and weight at 4 years. The effect of birthweight was weakened only by the addition of height at 15 years.

Multiple regression analysis of trunk length
The dietary effects (both individual nutrients and energy intake) were confounded with parental heights and father's social class and crowding. The effects of father's social class and crowding were confounded. Hence, as for the leg length analysis, the individual nutrients and crowding were not considered in further analyses.

In a multiple regression model (Table 4Go, column 2) those who were ill in childhood had an average trunk length 0.31 standard deviations less than those who were not ill, and those whose parents separated had a trunk length 0.24 standard deviations less than those whose parents did not. The unadjusted effects of these two variables are stronger in this restricted sample than in the sample used in Table 2Go. Energy intake was not independently associated with trunk length, although the unadjusted effect of energy intake in this reduced sample was slightly weaker (Table 4Go, column 1) than in the full sample. Addition of weight and height at 4 years to the model (Table 4Go, column 3) considerably weakened the effect of father's social class, which ceased to be significant. The effects of parental separation and childhood illness were also weakened both now indicating a quarter of a standard deviation difference. Weight and height were strongly and positively associated with trunk length.


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Table 4 Regression coefficients for the final model for trunk length (unadjusted and adjusted coefficients given for the same sample for comparison)
 
All later height measures showed a positive association with trunk length. The effect of childhood illness was attenuated when height at 15 years was included in the model. The effects of parental separation, birthweight and weight at 4 years remained broadly unaltered after inclusion of each height measure, although the effect of weight at 4 years was stronger in women than in men after adjustment for height at 15 years (P < 0.001 for interaction between weight at 4 years and sex).

The unadjusted coefficients in Tables 3 and 4GoGo are generally similar to those in Table 2Go with any slight discrepancies being due to the different samples used, most notably for the effects of serious illness and parental divorce on trunk length. When the analyses in Tables 2 and 3GoGo were rerun using the 1943 individuals with complete data on all measures the associations were unchanged.

Difference between leg and trunk length
No further modelling was carried out for this outcome as all associations became insignificant, and the effects were small, making interpretation difficult.

Discussion

Summary
In this analysis adult leg and trunk length were associated with the partial genetic and environmental effects of parental height and the developmental effect of birthweight and weight at 4 years. They differed in their apparent sensitivity to childhood environmental factors. Leg length was associated with breastfeeding and energy intake at 4 years. Trunk length was associated with childhood serious illness and less strongly with parental separation. Leg length is likely to have greater error than trunk length as it is calculated as the difference between standing and sitting heights, each with its associated error. The effects of likely errors in leg length measurement may have attenuated reported associations.

Diet
Validity of the dietary data is discussed elsewhere.26 Although error in this measure is certain, we argue that micronutrient rich foods, such as fish and fruit provide a sufficient indicator of diet to categorize children broadly on the range of nutrient intake. Dietary effects were, in this analysis, most evident on leg length, as found in another study.10 Nutrients associated with stature independently of energy were confounded with parental height and socioeconomic indicators such that no differentiation of effect of individual nutrients over that of energy intake was apparent.

Serious illness and parental separation
The association of shorter adult trunk length with childhood serious illness, and more weakly with parental separation, may be because these chronic effects continue into the period of more rapid trunk growth later in childhood.32 The change in unadjusted estimates for these variables on restriction of the sample size, and the small numbers experiencing these events means that the findings, particularly in relation to parental separation, should be interpreted with some caution. Childhood serious illness had long-term psychosocial and health effects in this and other studies.2,23,33,34 Long-term effects of parental separation have been associated with disturbances of behaviour, health and educational attainment;35–37 parental death did not have those long-term effects, implying that chronic parental discord is the explanation for this association. The proposed glucocorticoid-hippocampal hypothalamic pathway may account for this finding.19

Parental height
Mother's measured height was more strongly associated with offspring's leg and trunk length than was father's reported height, which was not linearly associated with leg length. This may be due to differences in measurement error since there were peaks of measures at even inches for father's but not mother's height. Children of manual social class fathers were shorter in both components of height, although this effect was confounded with parental height and child's weight at 4 years. It is likely that parental height is a marker of socioeconomic position.

Growth
In this analysis as in others38 the effect of birthweight was similar for leg and trunk length, even after adjustment for weight at 4 years which was positively associated with both components of height. Thus being heavy at birth or at 4 years, or both, had a positive effect on growth. The effect of birthweight on both components of adult height was independent of prepubertal childhood height. This suggests that prenatal growth does not have a differential influence on the components of height, but rather an influence on absolute height, as Gunnell et al.38 observed. There was also a positive effect of weight at 4 years on adult trunk length, which was stronger for women than men, after adjustment for height at 15 years. This was accounted for by later childhood height. Weight at 7 years is higher in girls who reach menarche early,39,40 and here early maturing boys and girls were also heavier at 4 years. Hence weight at 4 years may be a proxy for age at puberty, suggesting that early maturers have longer trunk length as a ratio of height than later maturers, as Gunnell et al.10 suggest. It is not clear, however, why it is more significant in girls.

Sensitivity of leg length to early environment
Leg length was associated with breastfeeding and energy intake, but not with serious illness and parental separation, showing the sensitivity of leg length as a marker of early life environment. This is supported by the argument that the national secular increase in adult height is reflected in height at 2 years, because of the reduction of stunting.30 The observed association may be stronger than reported because of the probable greater error in measurement of leg length.

Our interpretation that influences on early growth impact primarily on leg length while there are longer term effects of early factors on trunk length, is supported by regression models that included more than one measure of childhood height. The effects of energy intake and breastfeeding on leg length were weakened by the addition of height at 4 years, and weakened further by the addition of later heights. Dietary factors may influence growth before age 7 years. In contrast the effect of childhood serious illness was only decreased after adding height at 15 years, and that of parental separation remained weakly associated after adjustment for all heights. Given that height at 15 years is a measure of post pubertal height and is closely correlated to adult height, this effect may be accounted for by the effect of serious childhood illness on prepubertal height.

Period effect
Later born cohorts are likely to have increased exposure to some of the risks identified here. For example, the proportion of children living in relative poverty increased during the 1980s and early 1990s,41,42 breastfeeding is less prevalent but shows signs of increase,21,43 survival of low birthweight is more prevalent, and adult separation has risen greatly, with some maintenance of its adverse effects on growth19 and education.37 Studies of later born cohorts, without the constraints of food rationing, may find more variation in childhood nutrient intake, and more power to detect the effects of individual nutrients.

Conclusions

We found that leg length was sensitive to infant (under 5 years) socioeconomic circumstances and diet, whilst trunk length was sensitive to serious illness and possibly to chronic emotional disturbance. The explanation may be that leg growth is stronger than trunk growth during infancy, and trunk growth is stronger thereafter. Trunk length is apparently more rapid at later prepubertal ages,44 although in puberty trunk growth is not faster than leg growth.45 Trunk growth appeared more perturbed by factors that affected the child over longer periods between infancy and puberty. These two components of growth were independent of prenatal effects, as marked by weight at birth.


KEY MESSAGES

  • Adult leg and trunk length were positively associated with parental height, and own birthweight and weight at 4 years.
  • Leg length was positively associated with breastfeeding and with energy intake at 4 years.
  • Trunk length was associated negatively with serious illness experienced by the end of the fifth year, and possibly also with parental separation by the same age, but not with the dietary data.
  • Leg length may be sensitive to markers of early childhood environment because that is a period of rapid leg growth.
  • Trunk length may be sensitive to factors that have chronic effects on the child's life because more rapid trunk growth occurs at a later period, after infancy and before puberty.

 

Acknowledgments

This research was funded by the Medical Research Council.

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