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ORIGINAL RESEARCH COMMUNICATION |
1 From the Department of Pediatrics, Sunder Lal Jain Hospital, Delhi, India (SKB); the Department of Pediatrics, Maulana Azad Medical College, New Delhi, India (HSS); the Medical Research Council Epidemiology Resource Centre, University of Southampton, Southampton General Hospital, Southampton, United Kingdom (CHDF, CO, SDL, and DJPB); the Department of Cardiology, All India Institute of Medical Sciences, New Delhi, India (RL and KSR); and the Indian Council of Medical Research, New Delhi, India (SKDB)
2 The original cohort study was funded by the US National Center for Health Statistics and the Indian Council of Medical Research. The current study was supported by the British Heart Foundation and the Medical Research Council UK.
3 Reprints not available. Address correspondence to HS Sachdev, E-6/12 Vasant Vihar, New Delhi 110 057, India. E-mail: hpssachdev{at}hotmail.com.
| ABSTRACT |
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Objective: Anthropometric indexes of adult body composition were examined in relation to birth size and body mass index (BMI) during childhood.
Design: A population-based cohort of 1526 men and women aged 2632 y in Delhi, India, who were measured sequentially from birth until 21 y of age were followed up. Adult weight, height, skinfold thicknesses, and waist and hip circumferences were measured. BMI and indexes of adiposity (sum of skinfold thicknesses), central adiposity (waist-hip ratio), and lean mass (residual values after adjustment of BMI for skinfold thicknesses and height) were derived.
Results: Mean birth weight was 2851 g. As children, many subjects were underweight-for-age (>2 SDs below the National Center for Health Statistics mean; 53% at 2 y), but as adults, 47% were overweight, 11% were obese, and 51% were centrally obese (according to World Health Organization criteria). Birth weight was positively related to adult lean mass (P < 0.001) and, in women only, to adiposity (P = 0.006) but was unrelated to central adiposity. BMI from birth to age 21 y was increasingly strongly positively correlated with all outcomes. BMI and BMI gain in infancy and early childhood were correlated more strongly with adult lean mass than with adiposity or central adiposity. Higher BMI and greater BMI gain in late childhood and adolescence were associated with increased adult adiposity and central adiposity.
Conclusions: Birth weight and BMI gain during infancy and early childhood predict adult lean mass more strongly than adult adiposity. Greater BMI gain in late childhood and adolescence predicts increased adult adiposity.
Key Words: Body composition lean mass obesity developmental origins of adult disease birth weight childhood growth nutritional transition India
| INTRODUCTION |
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Considerable interest currently exists in the associations between growth in early life (fetal life, infancy, childhood, and adolescence) and the later development of obesity and obesity-related disease. Higher weight or BMI, or accelerated gain in weight or BMI, during childhood and adolescence is associated with a higher adult BMI (13, 14) and with an increased risk of adult hypertension (15), type 2 diabetes (1618), and IHD (1922). Paradoxically, however, although higher birth weight predicts higher adult BMI (14, 23, 24), it is associated with a lower risk of type 2 diabetes and IHD (18, 22, 2529), an exception being high birth weight caused by maternal diabetes, which is associated with an increased risk of later type 2 diabetes (29, 30). Higher weight or BMI in infancy is also associated with higher adult BMI (14) but a lower risk of type 2 diabetes and IHD (18, 22, 2527). One possible explanation for these discrepancies is that weight gain at different periods of early life may have differential effects on the acquisition of fat and lean mass. There is good evidence, for example, that higher birth weight is associated more strongly with increased adult lean body mass than with adult adiposity (3137).
We recently reported data from a cohort of young adults who were born in Delhi, India, and whose weight and height were measured at birth and throughout infancy, childhood, and adolescence (38). Lower BMI in infancy and accelerated BMI gain from 2 y onward were associated with an increased risk of adult type 2 diabetes and impaired glucose tolerance. Here we describe the relation of the early growth of this cohort with their adult body composition.
| SUBJECTS AND METHODS |
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Current study
From August 1998 to August 2002, we retraced 2584 (32%) of the initial cohort. They were visited at home by a social worker who explained the study, obtained consent, and administered a questionnaire. Ethical approval for the study was granted by the All India Institute of Medical Sciences, and informed consent was obtained from each subject.
Questionnaire data
Education was recorded as 1 of 7 categories ranging from "no schooling" (category 1) to "professional degree" (eg, Master of Science degree, PhD, or medical qualification) and occupation as 1 of 6 categories ranging from "unemployed" (category 1) and "unskilled manual labor" (category 2) to "professional." Housewives were categorized according to their husbands' occupations. Information on material possessions was recorded as an indicator of socioeconomic status. Subjects were given a score of 1 for each of the following household items: electricity, fan, bicycle, radio, motorized 2-wheeled vehicle, gas stove, television, cable television, electric mixer, electric grinder, electric air cooler, washing machine, car, air conditioner, computer, television antenna, and telephone. Alcohol consumption was recorded as the frequency of intake and volume of spirits, beer, and wine consumed per week. These data were converted into units of alcohol (1 unit = 25 mL spirits, 282 mL beer, or 125 mL wine) and were categorized as none, <7 units/wk, 714 units/wk, and >14 units/wk. Tobacco consumption was recorded as whether the subjects smoked (cigarettes, bidis, cigars, or hookah), chewed (raw tobacco or with pan), or inhaled (snuff). Subjects were categorized simply as current tobacco users or as nonusers. A score was derived as a summary estimate of daily physical activity. Work-related activity was classified on a 6-point scale ranging from "almost entirely sedentary" to "heavy physical work." Additional time spent per day in domestic activities (eg, sweeping, washing clothes, and cooking) and leisure activities (eg, jogging, swimming, and yoga) was recorded. Distances walked and cycled each day, with and without a load, were recorded and converted into approximate periods of time spent in these activities. These were then multiplied by metabolic constants, which were derived from the relative energy expenditure of activities (39), and were summed to derive a score.
Clinic investigations
After the home visit, the subjects were asked to attend a clinic after fasting overnight. Their weight, height, waist and hip circumferences, midupper arm circumference, and skinfold thicknesses (triceps and subscapular) were measured by using standardized techniques. The upper measurable limit for skinfold thickness was 40 mm. BMI was calculated as weight/height2 (in kg/m2). Subjects were categorized as obese if their BMI was
30 (40). Two definitions of overweight were used: the standard World Health Organization (WHO) cutoff of 25 (40) and that recently recommended for Asians of 23 (2). Central obesity was defined by using WHO criteria: waist-hip ratio > 0.90 (males) or > 0.85 (females) (41).
Two indexes of adiposity were derived from the skinfold-thickness measurements: 1) the sum of subscapular and triceps skinfold thicknesses, and 2) percentage body fat (42, 43). Three indexes of lean mass were derived: 1) arm muscle area, which was derived from midupper arm circumference and triceps skinfold thickness and was corrected for arm bone area (44); 2) lean body mass, which was derived as body weight minus fat mass and was adjusted for height, where fat mass = weight x percentage body fat; and 3) the residual value from a linear regression predicting BMI from the sum of skinfold thicknesses and height, adjusted for age and sex (designated the "lean residual"). The adjustments for height in these calculations were intended to derive proxies for lean tissue other than bone. Height adjustment was included in the derivation of the lean residual from BMI, even though BMI is often uncorrelated with height, because in Delhi there was a positive association between BMI and height (r = 0.09, P = 0.007 in men and r = 0.10, P = 0.009 in women).
Systolic and diastolic blood pressures were recorded by using an automated device (Omron 711; Omron Healthcare Europe, Hoosddorp, Netherlands) while the subjects were seated and after they had rested for 5 min. As described previously (38), plasma glucose and insulin concentrations were measured while the subjects were fasting and 120 min after a standard 75-g oral anhydrous glucose load. Plasma glucose, triacylglycerol, and cholesterol concentrations were analyzed by standard enzymatic methods by using Randox kits (Randox Laboratories Limited, Crumlin, United Kingdom) on a Beckman autoanalyzer (Beckman Instruments Inc, Brea, CA). HDL cholesterol was estimated by using the same method as for cholesterol measurement, after precipitation with phosphotungstate. Aliquots of plasma were stored at 70°C for up to 8 mo and were analyzed for insulin concentrations in batches by radioimmunoassay (Coat-a-Count insulin kit; Diagnostic Products Corporation, Los Angeles, CA). The method had intraassay and interassay CVs of <5% and <7.5%, respectively. Insulin resistance was calculated by homeostasis model assessment. Biochemical measurements were made in the biochemistry laboratory of the Department of Cardiology, All India Institute of Medical Sciences, New Delhi.
Statistical analyses
Variables with skewed distributions were log-transformed. Data were analyzed by using partial correlation coefficients and multiple linear regression. As previously described (38), we used all recorded data (not just the data for subjects recruited for this study) to derive SD scores for height and BMI for each subject at age 6 mo and at birthdays from age 1 to 21 y. The SD score is the number of SDs by which an observation differs from the mean for the cohort. Interpolated values were used if a measurement had been made within 6 mo (up to 1 y), 1 y (age of 2 y), 1.5 y (age of 3 y), and 2 y (all older ages). Back transformation provided estimates of the measurements at these ages. To measure the change in BMI in a time interval during childhood (for example between the ages of 2 and 5 y), we regressed the value at the end of the interval (age 5 y) on the value at the beginning of the interval (age 2 y) and at all preceding time points (birth, 6 mo, and 1 y) and expressed the residual as an SD score. This produces uncorrelated variables describing BMI change at specific time points in childhood, which we refer to as conditional SD scores. We calculated the age at adiposity rebound as the birthday between 2 and 9 y at which the lowest estimate of BMI occurred.
| RESULTS |
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0.1 SD lower.
The characteristics of the 886 men and 640 women studied are shown in Table 1
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30). Almost one-half of the subjects were overweight by the WHO definition (BMI
25), and nearly two-thirds were overweight by the Asian cutoff (BMI
23). Sixty-five percent of the men and 31% of the women were centrally obese.
To select the most appropriate indexes of body composition for the analysis, we correlated BMI, height, and the direct and derived measures of adiposity, central adiposity, and lean mass with the cardiovascular risk factor variables (Table 2
). Skinfold thicknesses, percentage body fat, waist circumference, and waist-hip ratio were positively correlated with all the risk factors except HDL cholesterol, for which the correlation was negative. The subscapular-triceps ratio showed weak and mainly nonsignificant correlations with the risk factors. The indexes of lean mass were also positively correlated with the risk factors (negatively with HDL cholesterol), especially insulin resistance and blood pressure, although these correlations were less strong than those for the measures of adiposity. For subsequent analyses, we limited the outcome variables to BMI and 4 other body-composition variables: sum of skinfold thicknesses and waist-hip ratio as the measures of general and central adiposity, respectively, that were most strongly correlated with the risk factors; the lean residual as the measure of lean mass least correlated with the risk factors; and height as the measure of skeletal size. Waist-hip ratio was selected in preference to waist circumference because it was uncorrelated with height. The correlations of each of these 4 variables with the risk factors, adjusted for the other 3, were weaker than but generally in the same direction as those described above (bottom of Table 2
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Adult body composition in relation to size at birth
In the sexes combined, higher birth weight was associated with higher adult lean residual and taller adult height (Table 3
) . In women, but not men, it was associated with higher adult BMI and sum of skinfold thicknesses (P values for the interaction between sex and birth weight were 0.006 for BMI and 0.01 for sum of skinfold thicknesses). Longer birth length was strongly associated with taller adult height. It was also associated with higher adult sum of skinfold thicknesses and lean residual and with higher BMI in women but not men (P for sex interaction 0.04). Ponderal index at birth was positively related to adult lean residual but to none of the other adult body-composition outcomes. None of the birth measurements was related to adult waist-hip ratio. Although it was not one of the selected variables, we examined adult subscapular-triceps ratio in relation to size at birth, because this has been reported frequently in the literature (24). The ratio was negatively associated with birth weight (P < 0.001), length (P = 0.02), and ponderal index (P = 0.01). There were no significant interactions between birth size and sex. Means fell from 1.48 and 1.00 in men and women, respectively, who weighed
2500 g at birth to 1.38 and 0.95 in those who weighed >3250 g.
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2500 g) and BMI change]. There were no significant interactions at any age for the other adult outcomes. These analyses show that the differences in the correlations between BMI gain in infancy and adult lean residual compared with adult sum of skinfold thicknesses were lower in subjects born prematurely or small for gestational age.
Adult body composition in relation to the adiposity rebound
The mean (±SD) age and BMI at adiposity rebound were 6.6 ± 1.7 y and 13.8 ± 0.9, respectively. As reported previously (38), lower BMI at 2 y (P < 0.001) and a low gain in BMI from birth to 2 y (P = 0.003) were associated with earlier adiposity rebound. Earlier rebound predicted an increase in all measurements of adult body composition (P
0.001) except height.
Adult body composition in relation to height during earlier life
Length or height during infancy, childhood, and adolescence were increasingly strongly positively correlated with adult height (Figure 3). There were steep increases in the correlation coefficients during infancy and adolescence. Correlations between earlier height, or changes in height SD score, and adult sum of skinfold thicknesses, lean residual, and waist-hip ratio were weak and generally not significantly different from each other. There was no evidence of increased adiposity or central adiposity in subjects who were short or stunted [<2 SDs shorter than the NCHS reference (45)] at any time during childhood.
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| DISCUSSION |
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The subjects came from an original population representing all live births within a defined area. The subjects' families were affluent and well-educated compared with national averages. Only 19% of the original cohort participated, and the subjects are thus likely to be unrepresentative of the original sample. The differences in their mean size at birth and during infancy and childhood, however, although statistically significant, were trivial. Our analysis was based on internal comparisons within the study sample and would be biased only if the associations between early growth and adult body composition differed between those who were and those who were not traced. Adult body composition was assessed only anthropometrically. None of our indexes of adiposity or lean mass was ideal, although all have been used in population studies. We recognize that our findings need to be confirmed with the use of better methods of assessing body composition.
We found expected associations between measures of adult adiposity and cardiovascular disease risk factors. Insulin resistance and blood pressure were also positively related to indexes of lean mass. The most likely explanation is that the latter were inadequately adjusted for body fat, especially nonsubcutaneous fat. The associations may, however, reflect a biological relation; several studies have reported positive associations between muscularity and blood pressure, although the mechanisms are unclear (46, 47). The subscapular-triceps ratio was positively correlated with cardiovascular disease risk factors in other studies (48, 49), but the mainly nonsignificant relations observed in Delhi suggest that this ratio has limited clinical utility at this age in this population.
Several studies have reported higher adult BMI in individuals of higher birth weight (23, 24). In common with other studies (3137, 50), our data showed that birth weight was more strongly related to the lean than to the fat component of adult BMI. This difference was more marked in males than in females; higher birth weight in females was also associated with increased adiposity. There was a similar sex difference in one study (37), although others reporting data for both sexes showed no sex differences (31, 33, 34, 36); higher birth weight was significantly associated with muscle mass (31) or fat-free mass (33, 34, 36) but not fat mass in both sexes. Our data are consistent with the suggestion that fetal life is a critical period for the development of muscle or visceral mass (26, 35, 51). This may explain the increased risk of insulin resistance and type 2 diabetes in persons of low birth weight (18, 27, 29) despite lower adult BMI.
The positive correlations between adult BMI and BMI in earlier life, which strengthened with increasing age, have also been reported elsewhere (13). A novel finding of our study was the differing associations with fat and lean components of adult body mass depending on the age of BMI measurement in earlier life. Higher BMI gain in infancy and early childhood was associated with a greater increase in adult lean mass than in adult adiposity. Higher BMI gain in late childhood and adolescence was strongly associated with adult adiposity and central adiposity. As previously described in the Delhi cohort (38) and in Europeans (18, 27), lower BMI in infancy and greater BMI gain during childhood and adolescence are associated with an increased risk of adult impaired glucose tolerance and type 2 diabetes. Our data may provide an explanation for these findings. Low adult muscle mass could explain the association between adult glucose intolerance and low BMI in infancy, whereas increased generalized and central adiposity could explain its association with accelerated BMI gain in later childhood and adolescence. Skeletal muscle cells lose their ability to divide in early postnatal life (51, 52). In animals, undernutrition at this time permanently reduces muscle mass, and enhanced nutrition at later ages results in excessive fat deposition (52). We propose that infancy, like fetal life, is a critical period for the development of lean mass. The susceptibility of South Asians to type 2 diabetes and IHD may partly be caused by poor development of lean mass in fetal life and infancy, combined with increased adiposity in later childhood resulting from urban transition. Several other studies have examined adult body composition in relation to weight and BMI gain in infancy (50, 53, 54), but none compared the strength of associations for fat and lean measurements. In Guatemala, Li et al (37) studied anthropometric measurements of adult body composition in relation to birth length and changes in length during the first 2 postnatal years. In both sexes, a greater increase in length between birth and 2 y was associated with stronger effects on adult fat-free mass than on fat mass.
Debate currently exists about optimal infant weight gain. Randomized trials of different infant feeds in preterm and growth-restricted neonates have shown that rapid infant weight gain is associated with increased cardiovascular disease risk factors later in childhood (55), which suggests that rapid weight gain during infancy could be harmful. Our data indicate that associations between early postnatal growth and later body composition may vary according to gestational age at birth and fetal growth rates, and this needs to be investigated further. The findings for full-term infants and those who were not small for gestational age suggest that infancy may be a window of opportunity during which better nutrition and greater BMI gain could increase adult lean mass. Infant weight gain is an important issue in developing countries, where the emphasis is still on eradicating undernutrition and where it is routine practice to encourage weight gain in small infants because of evidence that this increases infant survival (56), prevents stunting (57), and enhances cognitive development (58).
In contrast with the findings in infancy, accelerated BMI gain in later childhood and adolescence was clearly associated with increased adult adiposity and central adiposity. As previously described, it was also associated with an increased risk of impaired glucose tolerance and type 2 diabetes (38). As a population, our subjects had low BMI values in childhood compared with international reference data. Those who went on to develop diabetes had accelerated BMI gain after infancy, becoming "obese relative to themselves," but did not have a high BMI in absolute terms. Efforts to prevent obesity-related disease should start in childhood and should probably target not only children who are frankly overweight or obese but also those who are silently moving up the BMI percentiles. Serial BMI measurements and appropriate local reference standards would be needed to recognize this trajectory. Pediatricians would also need to develop effective ways of preventing children from acquiring excessive adipose tissue without impairing lean mass and skeletal growth.
| ACKNOWLEDGMENTS |
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SKB established the original cohort and designed the current study along with CHDF and DJPB. The data were analyzed and interpreted and the manuscript written by HSS, CHDF, and CO. Significant contributions were also made by SDL and SKDB (data collection and analysis), RL (laboratory analyses), and KSR (provision of advice on study design and data interpretation). None of the authors had a financial, commercial, or personal conflict of interest.
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