Insulin resistance is higher in prepubertal girls but switches to become higher in boys at age 16: A Cohort Study (EarlyBird 57)

BACKGROUND

The risk of type 2 diabetes is increasing in teenage girls, and is associated with their greater insulin resistance (IR).

HYPOTHESIS

We hypothesized that the adverse metabolic profile of girls (compared with boys) would persist from childhood through adolescence.

PATIENTS AND METHODS

Community-based longitudinal cohort of 292 children (147 boys) studied annually from 9 to 16 years.

MEASURES

IR (homeostasis-model-assessment-2), high-density lipoprotein-cholesterol (HDL-C), triglycerides, % body-fat (dual-energy x-ray absorptiometry), pubertal stage (age at peak height velocity), physical activity (accelerometry). Multi-level modelling established the age-related trends in IR and lipids and the influence of covariates.

RESULTS

Each year from 9 to 15 years, girls had 21% to 63% higher IR than boys (girls mean IR 0.73-1.33, boys 0.51-0.89, P < .005). At 16 years the gender difference was not significant (girls IR 0.60, boys 0.56, P = .45). Girls had lower HDL-C from 9 to 12 years, higher triglycerides from 9 to 14 years, greater adiposity throughout, and earlier puberty, but boys were more active than girls (all P < .05). After adjustment for %-fat, puberty and activity, the gender difference in IR between girls and boys aged 9 to 15 years became non-significant (IR girls 0.66-1.01, boys 0.65-1.04, P > .07). However, after adjustment at 16 years, girls' IR was 25% lower than boys' (girls 0.44, boys 0.63, P = .001), and they had 22% higher HDL-C (P < .001) and 20% lower triglycerides (P = .003).

CONCLUSIONS

The higher IR of prepubertal and early pubertal girls diminishes during late puberty, and boys begin to exhibit greater metabolic risk. Despite being leaner and more active, boys at 16 years have higher IR than girls, suggesting future higher risk for diabetes, thus we reject our hypothesis.

Physical activity attenuates the mid-adolescent peak in insulin resistance but by late adolescence the effect is lost: a longitudinal study with annual measures from 9-16 years (EarlyBird 66)

AIMS/HYPOTHESIS

The aim of this work was to test whether the mid-adolescent peak in insulin resistance (IR) and trends in other metabolic markers are influenced by long-term exposure to physical activity.

METHODS

Physical activity (7 day ActiGraph accelerometry), HOMA-IR and other metabolic markers (glucose, fasting insulin, HbA1c, lipids and BP) were measured annually from age 9 years to 16 years in 300 children (151 boys) from the EarlyBird study in Plymouth, UK. The activity level of each child was characterised, with 95% reliability, by averaging their eight annual physical activity measures. Age-related trends in IR and metabolic health were analysed by multi-level modelling, with physical activity as the exposure measure (categorical and continuous) and body fat percentage (assessed by dual-energy X-ray absorptiometry) and pubertal status (according to age at peak height velocity and Tanner stage) as covariates.

RESULTS

The peak in IR at age 12-13 years was 17% lower (p < 0.001) in the more active adolescents independently of body fat percentage and pubertal status. However, this difference diminished progressively over the next 3 years and had disappeared completely by the age of 16 years (e.g. difference was -14% at 14 years, -8% at 15 years and +1% at 16 years; 'physical activity × age(2), interaction, p < 0.01). Triacylglycerol levels in girls (-9.7%, p = 0.05) and diastolic blood pressure in boys (-1.20 mmHg, p = 0.03) tended to be lower throughout adolescence in the more active group.

CONCLUSIONS/INTERPRETATION

Our finding that physical activity attenuates IR during mid-adolescence may be clinically important. It remains to be established whether the temporary attenuation in IR during this period has implications for the development of diabetes in adolescence and for future metabolic health generally.

Awareness of body weight by mothers and their children: repeated measures in a single cohort (EarlyBird 64)

BACKGROUND

Mothers often do not realize when their child is overweight. We aimed to compare mothers' perceptions of children's weight before and during puberty, and to explore factors at 7 years predicting recognition of overweight at 16 years.

METHODS

Mothers of 237 children (136 boys) from the EarlyBird study estimated their own weight category and that of their child aged 7 years and 16 years. The children estimated their own weight category at 16 years. Annual measures: body mass index standard deviation score (BMIsds), per cent fat, physical activity. Pubertal development assessed by age at peak height velocity (APHV). MATERNAL MEASURES: BMI, education, socio-economic status.

RESULTS

At 7 years 21% of girls and 16% of boys were overweight or obese, rising to 27% and 22% respectively at 16 years. The accuracy of the mother's perception of her child's weight category improved from 44% at 7 years to 74% at 16 years, but they were less able to judge overweight in sons than daughters. The mothers' level of concern about overweight was greater for girls than boys, and increased for girls (52% mothers of overweight/obese girls were worried at 7 years, 62% at 16 years), but remained static in the boys (42% vs. 39%). Over 80% of the youngsters realized when they were overweight, but 25% normal-weight girls also classed themselves as overweight. Only BMI predicted a mother's ability to correctly perceive her child's weight. Neither her awareness, nor concern, about the child's weight at 7 years had any impact on the trajectory of the child's BMI from 7 years to 16 years.

CONCLUSIONS

Parents are central to any successful weight reduction programme in their children, but will not engage while they remain ignorant of the problem. Crucially, any concern mothers may have about their child's excess weight at 7 years appears to have no impact on subsequent weight change.

PGC1α promoter methylation in blood at 5-7 years predicts adiposity from 9 to 14 years (EarlyBird 50)

The early environment, acting via epigenetic processes, is associated with differential risk of cardiometabolic disease (CMD), which can be predicted by epigenetic marks in proxy tissues. However, such measurements at time points disparate from the health outcome or the environmental exposure may be confounded by intervening stochastic and environmental variation. To address this, we analyzed DNA methylation in the peroxisome proliferator-activated receptor γ coactivator 1α promoter in blood from 40 children (20 boys) collected annually between 5 and 14 years of age by pyrosequencing. Body composition was measured annually by dual X-ray absorptiometry, physical activity by accelerometry, and pubertal timing by age at peak high velocity. The effect of methylation on transcription factor binding was investigated by electrophoretic mobility shift assays. Seven cytosine guanine dinucleotide (CpG) loci were identified that showed no significant temporal change or association with leukocyte populations. Modeling using generalized estimating equations showed that methylation of four loci predicted adiposity up to 14 years independent of sex, age, pubertal timing, and activity. Methylation of one predictive locus modified binding of the proadipogenic pre-B-cell leukemia homeobox-1/homeobox 9 complex. These findings suggest that temporally stable CpG loci measured in childhood may have utility in predicting CMD risk.

Metabolic risk in contemporary children is unrelated to socio-economic status: longitudinal study of a UK urban population (EarlyBird 42)

Lifestyle interventions to improve health in young children tend to target areas of relative deprivation, but the evidence for so doing is largely historical. Accordingly, we have re-examined the link between deprivation, obesity and metabolic risk in contemporary UK children. Using a postcode-based index of multiple deprivation (IMD), we assessed 269 children from the community-based EarlyBird Study, attending 53 schools representing a wide socio-economic range. Annual measures of fatness from 5 to 8 yr included body mass index (BMI), waist circumference (WC), and sum of five skinfolds (SSF). A metabolic risk score, based on blood pressure, lipids and insulin resistance, was derived from annual fasting blood samples. There were no significant associations between deprivation and any measure of adiposity in girls (all p > 0.37). In boys, there was a weak but consistently inverse relationship between deprivation and WC (r = -0.19, p = 0.03) and BMI (r = -0.14, p = 0.09) at 8 yr. Changes in adiposity over 3 yr were unrelated to deprivation in boys. In girls there was a slight but significant increase in SSF only (1 mm/yr per 20 IMD units, p = 0.001). Importantly, in both genders, metabolic risk score was unrelated to deprivation throughout (r values -0.05 to -0.13, all p > 0.12), as was change in metabolic risk (all p > 0.30). Our data do not support the assumption that obesity, metabolic disturbance and thus risk of type 2 diabetes are more prevalent among poorer children. In today's increasingly obesogenic environment, youngsters from all backgrounds appear to be vulnerable, with population-wide implications for public health spending, and the prevention of diabetes in contemporary youth.

Divergence between HbA1c and fasting glucose through childhood: implications for diagnosis of impaired fasting glucose (Early Bird 52)

OBJECTIVE

An HbA1c threshold of ≥ 6.5% has recently been adopted for the diagnosis of diabetes in adults, and of ≥ 5.7% to identify adults at risk. Little,however, is known of HbA1c's behaviour or diagnostic value in youth. Our aim was to describe the course of HbA1c during childhood, and its association with fasting glucose.

RESEARCH DESIGN AND METHODS

HbA1c and glucose were measured every year in a cohort of 326 healthy children (162 boys) from 5 to 15 years. Mixed effects modelling was used to establish the determinants of HbA1c and its development over time. ROC analysis was used to determine the diagnostic value of HbA1c in the 55 individuals who showed impaired fasting glucose(IFG – glucose ≥ 5.6 mmol/L).

RESULTS

Glucose rose progressively from 4.3 mmol/L at 5 years to 5.1 mmol/Lat 15 years, and although there were positive associations between HbA1c and glucose, from 10 to 13 years, HbA1c fell while glucose continued to rise. IFG developed in 55 children, but HbA1c exceeded 5.7% in only 16 of them. The maximum area under the ROC curve was 0.71 at the age of 14 (p<0.001), and the sensitivity and specificity were optimal at 50 and 80% respectively,corresponding to HbA1c of 5.4%.

CONCLUSIONS

Although HbA1c retains a positive association with glucose throughout childhood, it is weak, and their trends diverge from 10 years,suggesting that factors other than glycaemia systematically influence the variance of HbA1c in youth. These findings therefore limit the interpretation of HbA1c for the diagnosis of IFG during childhood.

Body fat in children does not adversely influence bone development: a 7-year longitudinal study (EarlyBird 18)

WHAT IS ALREADY KNOWN ABOUT THIS SUBJECT

Both negative and positive associations have been reported between body fat and bone density. Extra mechanical loading from excess fat may lead to greater bone mass. Excess ectopic fat may lead to bone demineralisation through inflammatory pathways.

WHAT THIS STUDY ADDS

Longitudinally collected data from narrow-angle beam densitometry gives a novel insight into bone growth through adolescence. There is no evidence of a deleterious effect of body fat on children's growing bones after adjustment for height and age. Body fat, mediated by puberty, is associated with larger bones in boys and bones that are both denser and larger in girls.

OBJECTIVE

Bone growth is an important determinant of peak bone mass and fracture risk, but there is limited data on the impact of fat-on-bone development at a time when childhood obesity is reaching epidemic proportions. Accordingly, we explored the effect of body fat (BF) on bone growth over time in the context of age, pubertal tempo and gender.

METHOD

A cohort of 307 children was measured biannually from 9-16 years for height and weight, and every 12 months for percent BF, bone area (BA), bone mineral content and areal bone mineral density (aBMD) by dual-energy X-ray absorptiometry. Pubertal tempo was determined quantitatively by age at peak height velocity.

RESULTS

Percent BF increased and then fell in the boys, but increased throughout in the girls. aBMD and BA increased in both genders (P < 0.001). Greater BF was associated with higher aBMD and BA in girls (P < 0.001), but only BA in boys (P < 0.001). The extra aBMD associated with increased BF was greater in older girls. The rise in aBMD and BA was associated with earlier puberty in both genders (P < 0.001). The impact of BF on aBMD was greater in later puberty in girls (0.0025 g cm(-2) per 10% BF at 10 years versus 0.016 g cm(-2) per 10% BF at 14 years, P < 0.001).

CONCLUSION

Greater BF is associated with larger bones, but also denser bones in girls. The effects of fat and puberty are complex and gender specific, but BF of contemporary UK children does not appear to be deleterious to bone quality.

Evidence of early beta-cell deficiency among children who show impaired fasting glucose: 10-yr cohort study (EarlyBird 56)

OBJECTIVE

Impaired fasting glucose (IFG) is a predictor of future diabetes and is increasingly common in children, but the extent to which it results from excess insulin demand or failure of supply is unclear. Our aim was to compare the behaviour of insulin sensitivity and beta-cell function in children who developed IFG with those whose glucose levels remained within the normal range.

METHODS

We examined trends in fasting glucose, insulin sensitivity (HOMA-S) and beta-cell function (HOMA-B) in 327 healthy children annually from 5 to 15 yr, and the parents at baseline.

RESULTS

Fifty-five children showed IFG, mostly after age 11 yr. Fasting glucose rose progressively and was higher throughout in those who developed IFG compared with those who did not (p < 0.001). Beta-cell function was lower from the age of 5 yr in those who developed IFG (p = 0.006), but there was no difference in BMI (p = 0.71). A difference in insulin sensitivity was revealed on adjustment for covariates (p = 0.03). Glucose was higher (p < 0.001), beta-cell function lower (p = 0.01), and insulin sensitivity the same (p = 0.86) in the mothers of children who showed IFG, compared with those who did not.

CONCLUSIONS

IFG is common in contemporary children, and appears to be related to a defect in beta-cell function already present at 5 yr. Similar findings in the mothers of IFG children suggest that the beta-cell defect may be transmissible.

The contribution of parental BMI to the metabolic health of their offspring: a longitudinal cohort study (EarlyBird 55)

OBJECTIVE

The objective of this study was to establish the extent to which parental factors influence the metabolic health of their offspring.

DESIGN

The study was designed as a prospective longitudinal cohort study

SUBJECTS

The study's subjects were 226 healthy trios from a 1995 to 1996 birth cohort randomly recruited in the city of Plymouth, UK MEASUREMENTS: Body mass index (BMI) and metabolic z-score (derived from natural log HOMA-IR, triglycerides, total/high-density lipoprotein cholesterol ratio), measured at nine annual time points, from 5 to 13 years.

RESULTS

As expected, the metabolic z score was closely related to BMI in both genders and at all ages (r = 0.40-0.57, P < 0.001). Accordingly, there were large and significant differences in the metabolic z-score between children categorized as normal weight or overweight/obese. At 13 years, for example, the metabolic z score of the overweight/obese girls was 14-fold greater than that of the normal-weight girls (P < 0.001). However, parental BMI and metabolic status had little effect on these differences. Indeed, mixed effects modelling showed that, as the child's BMI increased, so the influence of parental factors became less relevant. Time-lag analyses confirmed that weight gain preceded metabolic disturbances in the children.

CONCLUSION

The impact of obesity on the metabolic health of contemporary children is a function of their own weight gain, rather than that of their parents, and is therefore potentially preventable.

Age before stage: insulin resistance rises before the onset of puberty: a 9-year longitudinal study (EarlyBird 26)

OBJECTIVE

Insulin resistance (IR) is associated with diabetes. IR is higher during puberty in both sexes, with some studies showing the increase to be independent of changes in adiposity. Few longitudinal studies have reported on children, and it remains unclear when the rise in IR that is often attributed to puberty really begins. We sought to establish from longitudinal data its relationship to pubertal onset, and interactions with age, sex, adiposity, and IGF-1.

RESEARCH DESIGN AND METHODS

The EarlyBird Diabetes study is a longitudinal prospective cohort study of healthy children aged 5-14 years. Homeostasis model assessment (HOMA-IR), skinfolds (SSF), adiposity (percent fat, measured by dual-energy X-ray absorptiometry), serum leptin, and IGF-1 were measured annually in 235 children (134 boys). Pubertal onset was adduced from Tanner stage (TS) and from the age at which luteinizing hormone (LH) first became serially detectable (≥0.2 international units/L).

RESULTS

IR rose progressively from age 7 years, 3-4 years before TS2 was reached or LH became detectable. Rising adiposity and IGF-1 together explained 34% of the variance in IR in boys and 35% in girls (both P < 0.001) over the 3 years preceding pubertal onset. The contribution of IGF-1 to IR was greater in boys, despite their comparatively lower IGF-1 levels.

CONCLUSIONS

IR starts to rise in mid-childhood, some years before puberty. Its emergence relates more to the age of the child than to pubertal onset. More than 60% of the variation in IR prior to puberty was unexplained. The demography of childhood diabetes is changing, and prepubertal IR may be important.

Fatness leads to inactivity, but inactivity does not lead to fatness: a longitudinal study in children (EarlyBird 45)

OBJECTIVE

To establish in children whether inactivity is the cause of fatness or fatness the cause of inactivity.

DESIGN

A non-intervention prospective cohort study examining children annually from 7 to 10 years. Baseline versus change to follow-up associations were used to examine the direction of causality.

SETTING

Plymouth, England.

PARTICIPANTS

202 children (53% boys, 25% overweight/obese) recruited from 40 Plymouth primary schools as part of the EarlyBird study.

MAIN OUTCOME MEASURES

Physical activity (PA) was measured using Actigraph accelerometers. The children wore the accelerometers for 7 consecutive days at each annual time point. Two components of PA were analysed: the total volume of PA and the time spent at moderate and vigorous intensities. Body fat per cent (BF%) was measured annually by dual energy x ray absorptiometry.

RESULTS

BF% was predictive of changes in PA over the following 3 years, but PA levels were not predictive of subsequent changes in BF% over the same follow-up period. Accordingly, a 10% higher BF% at age 7 years predicted a relative decrease in daily moderate and vigorous intensities of 4 min from age 7 to 10 years (r=-0.17, p=0.02), yet more PA at 7 years did not predict a relative decrease in BF% between 7 and 10 years (r=-0.01, p=0.8).

CONCLUSIONS

Physical inactivity appears to be the result of fatness rather than its cause. This reverse causality may explain why attempts to tackle childhood obesity by promoting PA have been largely unsuccessful.

Direction of causality between body fat and insulin resistance in children--a longitudinal study (EarlyBird 51)

OBJECTIVE

To investigate the direction of causality in the association between adiposity and insulin resistance in children.

METHODS

Body composition by DEXA, and insulin resistance by HOMA-2 IR were measured annually in 238 children aged from 7-13 years. Longitudinal modelling was used to establish whether baseline and/or trends in adiposity were associated with change in IR or whether, conversely, baseline and/or trends in IR were associated with change in adiposity.

RESULTS

Baseline adiposity was associated with change in IR in the short-term (p < 0.001) but less so in the long-term (p < 0.09) in both genders. Baseline IR was not associated with short-term change in adiposity in either gender (p > 0.42). In the long-term, baseline IR appeared to be positively associated with change in adiposity in boys (p = 0.02) but inversely associated with change in adiposity (the higher the baseline IR, the lower the gain in %fat) in girls (p < 0.001).

CONCLUSIONS

The dominant direction of causality appears to be from adiposity to insulin resistance. In boys, adiposity appears to be both a cause and an effect of IR in the long term. In girls, however, higher insulin resistance appeared to limit further gain in body fat in the long term, an observation consistent with insulin desensitization as an adaptive response to weight gain.

The relationship of height and body fat to gender-assortative weight gain in children. A longitudinal cohort study (EarlyBird 44)

OBJECTIVE

Height, body fat and body mass index (BMI) are correlated in children, so we hypothesized that the gender-assortative associations in BMI recently reported in contemporary children might extend to their height and body fat.

DESIGN

Prospective longitudinal cohort study.

SUBJECTS

A total of 226 healthy trios (mother, father and child) from a 1995?1996 birth cohort randomly recruited in the city of Plymouth, UK.

MEASUREMENTS

Height, weight, and BMI (kg/m(2)) were measured in each of the parents and, in addition, sum of five skin-folds (SF) in their children at 5, 6, 7 and 8 y.

RESULTS

BMI and SF were strongly height-dependent in the children by 8 y (r = 0.41-0.56). SF was gender-assortative insofar as the mean SF was significantly greater in the daughters (but not the sons) of obese mothers (obese vs. normal weight: +2.5 cm p < 0.001) and in the sons (but not the daughters) of obese fathers (obese vs. normal: +1.3 cm p < 0.001). As expected, offspring height correlated with that of their parents, but overweight/obese children were systematically taller than normal weight children (boys: +1.02 SDS, girls: +1.14 SDS, p < 0.01), and this difference was independent of parental height or BMI.

CONCLUSIONS

Height is transmitted by both parents, and the body fat of overweight/obese children largely by the same-sex parent, but the extra height associated with more fat in the child is unrelated to the height or weight of either parent. The secular trend in height among contemporary children may simply reflect their rising body fat. Excess fat is unhealthy, so the trend in height may not be healthy either.

Changes in resting energy expenditure and their relationship to insulin resistance and weight gain: a longitudinal study in pre-pubertal children (EarlyBird 17)

BACKGROUND & AIMS

In adults, adjustments in resting energy expenditure (REE) are used to defend energy balance against disturbance caused by over-and under-nutrition, and may be linked to changes in insulin resistance and leptin. Little is known of these associations in children. Our aim was to test the hypothesis that long-term weight gain in children is met with adaptive changes in resting energy expenditure, mediated by insulin resistance and/or leptin.

METHODS

REE by indirect calorimetry, anthropometry, body composition by DEXA, insulin resistance (HOMA-IR) and serum leptin were measured annually in 232 children from the age of 7-10 y.

RESULTS

REE rose from 7 to 10 y, and the rise exceeded that predicted by the concurrent rise in fat and fat-free mass by 184 kcal/day in the boys and by 160 kcal/day in the girls. However, there were no significant relationships in either gender between this 'excess' rise in REE and change in body composition (r < or = 0.08, p > or = 0.42). The rise in both boys and girls was associated with, but not explained by, a rise in insulin resistance (p < or = 0.002). There was no association with serum leptin (p > or = 0.32).

CONCLUSIONS

The data do not support the hypothesis of adaptive changes in REE in pre-pubertal children, and insulin resistance explains very little of the pre-pubertal rise in REE. The rise in REE beyond that explained by changes in body composition may reflect an increase in energy requirements prior to puberty.

Objectively measured physical activity and its association with adiponectin and other novel metabolic markers: a longitudinal study in children (EarlyBird 38)

OBJECTIVE

Recent evidence suggests that, in children, traditional markers of metabolic disturbance are related only weakly to physical activity. We therefore sought to establish the corresponding relationships with newer metabolic markers.

RESEARCH DESIGN AND METHODS

This was a nonintervention longitudinal study of 213 healthy children recruited from 54 schools in Plymouth, U.K. MTI accelerometers were used to make objective 7-day recordings of physical activity at ages 5 +/- 0.3 (mean +/- SD), 6, 7, and 8 years. Overall physical activity was taken as the average of the four annual time points. The metabolic markers at 8 years were adiponectin, leptin, high-sensitivity C-reactive protein (hsCRP), and insulin resistance (homeostasis model assessment). Potential confounders included percent body fat measured by dual-energy X-ray absorptiometry and diet measured by food frequency questionnaire.

RESULTS

Whereas physical activity did not correlate with insulin resistance (r = -0.01), leptin (r = +0.04), or hsCRP (r = +0.01) independently of percent body fat, it did correlate with adiponectin, but inversely (r = -0.18, P = 0.02). This unexpected inverse relationship was strongest among the less active children (physical activity < median: r = -0.30, P = 0.01) but negligible in the more active children (physical activity > median: r = +0.04, P = 0.76). Adiponectin was significantly higher (0.52 SD, P < 0.01) in the least active tertile compared with the other two tertiles. Insulin resistance, however, did not differ across the physical activity tertiles (P = 0.62).

CONCLUSIONS

Adiponectin levels in children are highest among those who are least active, but their insulin resistance is no different. Adiponectin has a known insulin-sensitizing effect, and our findings are consistent with a selective effect at low levels of physical activity.

Adiponectin in childhood

Adiponectin, a hormone produced and secreted by adipocytes, is present in circulation in high circulating concentrations, suggesting an important physiological role. An indirect regulator of glucose metabolism, adiponectin increases insulin sensitivity, improves glucose tolerance and inhibits inflammation. Plasma adiponectin relates inversely to adiposity and, importantly, reflects the sequelae of accumulation of excess adiposity. The role of adiponectin in adults has been explored in detail. Studies in children are now available and, given the increasing rates of childhood obesity, it is important to establish the role of adiponectin in mediating insulin resistance and cardiovascular disease in this age group. This paper reviews the regulation of adiponectin, its effect on body mass, glucose metabolism and cardiovascular risk in infants, children and adolescents. It demonstrates clear links between adiponectin and features of the metabolic syndrome in obese children and adolescents. However, adiponectin's role as a predictor of metabolic dysfunction in healthy, normal-weight youngsters is less clear.

Contribution of early weight gain to childhood overweight and metabolic health: a longitudinal study (EarlyBird 36)

BACKGROUND

Early weight gain (0-5 years) is thought to be an important contributor to childhood obesity and consequently metabolic risk. There is a scarcity of longitudinal studies in contemporary children reporting the impact of early weight gain on metabolic health.

OBJECTIVE

We aimed to assess the impact of early weight gain on metabolic health at 9 years of age.

METHOD

Two hundred thirty-three children (134 boys, 99 girls) with a gestational age of >37 weeks were assessed at birth, 5 years of age, and 9 years of age. Measures included weight SD scores at each time point and excess weight gained (Delta weight SD score) between them. The outcome measure included composite metabolic score (sum of internally derived z scores of insulin resistance, mean blood pressure, triglyceride level, and total cholesterol/high-density lipoprotein cholesterol ratio).

RESULTS

Weight SD score increased by 0.29 SD score in girls and 0.26 SD score in boys from 0 to 5 years of age and by 0.03 SD score in girls and 0.11 SD score in boys from 5 to 9 years of age. Weight SD score correlated poorly to moderately before 5 years of age but strongly after 5 years of age. Birth weight SD score predicted (girls/boys) 2.4%/0% of the variability in composite metabolic score at 9 years of age. Adding Delta weight SD score (0-5 years old) contributed (girls/boys) 11.2%/7.0% to the score, and adding Delta weight SD score (5-9 years old) additionally contributed (girls/boys) 26.4%/16.5%. Importantly, once weight SD score at 9 years of age was known, predictive strength was changed little by adding Delta weight SD score.

CONCLUSIONS

Most excess weight before puberty is gained before 5 years of age. Weight at 5 years of age bears little relation to birth weight but closely predicts weight at 9 years of age. Single measures of current weight are predictive of metabolic health, whereas weight gain within a specific period adds little. A single measure of weight at 5 years of age provides a pointer to future health for the individual. If metabolic status at 9 years of age means future risk, diabetes/cardiovascular prevention strategies might better focus on preschool-aged children, because the die seems to be largely cast by 5 years of age, and a healthy weight early in childhood may be maintained at least into puberty.

Physical activity at the government-recommended level and obesity-related health outcomes: a longitudinal study (Early Bird 37)

BACKGROUND

In the UK and USA, government guidelines for childhood physical activity have been set (> or =60 min/day at > or =3 metabolic equivalents of thermogenesis (METs)), and body mass index (BMI) chosen as the outcome measure.

AIM

To determine the extent to which physical activity at the government-recommended intensity is associated with change in body mass/fat and metabolic health in pre-pubertal children.

METHODS

Non-intervention longitudinal study of 113 boys and 99 girls (born 1995/96) recruited from 54 schools. Physical activity (Actigraph accelerometers), changes in body mass (raw and age/gender-standardised BMI), fatness (skin-fold thickness and waist circumference) and metabolic status (insulin resistance, triglycerides, cholesterol/HDL ratio and blood pressure - separately and as a composite metabolic z score) were measured on four annual occasions (5, 6, 7 and 8 years).

RESULTS

Mean physical activity did not change over time in either sex. Averaging the 7-day recordings from four time points rather than one increased the reliability of characterising a child's activity from 71% to 90%. Some 42% of boys and 11% of girls met the guideline. There were no associations between physical activity and changes in any measurement of body mass or fatness over time in either sex (eg, BMI standard deviation scores: r = -0.02, p = 0.76). However, there was a small to moderate inverse association between physical activity and change in composite metabolic score (r = -0.19, p<0.01). Mixed effects modelling showed that the improvement in metabolic score among the more active compared to the less active children was linear with time (-0.08 z scores/year, p = 0.001).

CONCLUSIONS

In children, physical activity above the government-recommended intensity of 3 METs is associated with a progressive improvement in metabolic health but not with a change in BMI or fatness. Girls habitually undertake less physical activity than boys, questioning whether girls in particular should be encouraged to do more, or the recommendations adjusted for girls.

Children from low-income families have less access to sports facilities, but are no less physically active: cross-sectional study (EarlyBird 35)

BACKGROUND

Rising levels of childhood obesity have led to an increasing number of Government sponsored initiatives attempting to stem the problem. Much of the focus to date has been on physical activity and out-of-school activity in particular. There is an assumption that children from low-income families suffer most where there is a lack of structured physical education in school. Accordingly, provision of additional facilities for sport and other forms of active recreation tend to target areas of socio-economic deprivation.

AIM

We have assessed the relationship between parental income, the use of out-of-school sports facilities and the overall physical activity of young children across a wide socio-economic range.

METHODS

Total weekly physical activity was measured, objectively, over 7 days both at 7 years and 8 years in a healthy cohort of 121 boys and 93 girls using actigraph accelerometers. Questionnaires were used to establish parental income and parents reported the child's weekly use of out-of-school facilities for structured physical activity.

RESULTS

Children from low-income families attended significantly fewer sessions of structured out-of-school activities than those from wealthier families (r = 0.39), with a clear dose-response relationship across income groups. Nevertheless, total physical activity, measured objectively over seven continuous days, showed no relationship between parental income and the mean activity level of the children (r = -0.08). Nor did we find a relationship between parental income and time spent in higher intensity activity (r = -0.04).

CONCLUSION

Social inequality appears to have little impact on physical activity in young children. Those from poorer families make less use of facilities for structured activity out-of-school but they nevertheless record the same overall level of activity as others. What they lack in opportunity they appear to make up in the form of unstructured exercise. Improving provision for sport may not lead to the expected rise in activity levels in young children.

Distribution of adiponectin, leptin, and metabolic correlates of insulin resistance: a longitudinal study in British children; 1: Prepuberty (EarlyBird 15)

BACKGROUND

The emergence of type 2 diabetes in young populations has mirrored a rising prevalence of obesity and insulin resistance during childhood and adolescence. At the same time, the role of adipokines as links between obesity and insulin resistance is becoming more appreciated. We sought to establish age- and sex-specific distributions of metabolic correlates of insulin resistance in healthy prepubertal children.

METHODS

We collected fasting blood samples from a contemporary cohort of 307 British children at ages 5, 6, 7, and 8 years and measured insulin, glucose, triglycerides, total and HDL cholesterol, urate, glycohemoglobin, sex hormone-binding globulin (SHBG), leptin, and adiponectin. We used homeostasis model assessment (HOMA 2) to estimate insulin sensitivity (HOMA-%S) and beta-cell function (HOMA-%B). Anthropometric measures included body mass index.

RESULTS

Body mass index increased from age 5 to 8 years (P < 0.001). HOMA-%B decreased (P < 0.001) and HOMA-%S increased (P < 0.05), but glucose also increased (P < 0.001) whereas glycohemoglobin decreased (P < 0.001). Consistent with the rise in insulin sensitivity, HDL cholesterol increased (P < 0.001) and triglycerides decreased (NS), whereas adiponectin decreased (P = 0.02). The patterns were similar in boys and girls, although girls were less insulin sensitive throughout. Accordingly, triglycerides tended to be higher in the girls, and HDL cholesterol and SHBG lower.

CONCLUSIONS

The metabolic disturbances associated with insulin resistance appear to be more advanced in girls. Markers of metabolic health improve in both sexes from 5 to 8 years, despite rising adiposity.

Trends, associations and predictions of insulin resistance in prepubertal children (EarlyBird 29)

BACKGROUND

Rising obesity has been observed in all age groups. Anthropometric cut-points have been used to predict metabolic risk in children, although they are not based on known outcomes.

AIM

We examined the trends, associations and predictions of metabolic health from anthropometry in prepubertal children.

METHOD

Three hundred and seven healthy children were examined annually between 5 and 8 yr.

MEASURES

height, weight, body mass index (BMI), sum of skinfold thickness at five sites (SSF) and waist circumference (WC).

OUTCOME MEASURES

homeostasis model assessment of insulin resistance (HOMA-IR), high-density lipoprotein cholesterol (HDL-C) and triglycerides (TG).

RESULTS

Two hundred and thirty-one [131 boys (B) and 100 girls (G)] children had complete data sets at all four time points. (i) All measures of adiposity rose from 5 to 8 yr (BMI - B: +3.4%, G: +5.7%; WC - B: +10.4%, G: +11.8%; SSF - B: +23.3%, G: +30.7%, all p < 0.001). HOMA-IR unexpectedly fell (B: -16.6%, p = 0.01; G: -32.5%, p < 0.001). This fall was significant between 5 and 6 yr in both genders (5-6 yr - B: -17.8%, p < 0.001; G: -20.0%, p = 0.002) and between 6 and 7 yr in girls only (6-7 yr - B: -10.8%, p = 0.12; G: -19.2%, p = 0.001). HDL-C rose (B: +17.8%, G: +17.1%, both p < 0.001) and TG fell (B: -4.8%, p = 0.16; G: -11.6%, p = 0.006). (ii) Correlations between insulin resistance (IR) and anthropometry were poor at 5 yr but strengthened by 8 yr (BMI - B: r = 0.20/0.38, G: r = 0.28/0.49; WC - B: r = 0.25/0.40, G: r = 0.32/0.58; SSF - B: r = 0.11/0.36, G: r = 0.18/0.53). (iii) In girls, but not boys, adiposity at 5 yr predicted IR better at 8 yr (BMI - r(2 )= 0.17; WC - r(2 )= 0.28; SSF - r(2 )= 0.17, all p < 0.001) than it did at 5 yr (BMI - r(2 )= 0.08, p < 0.01; WC - r(2 )= 0.10, p < 0.01; SSF - r(2 )= 0.03, p = 0.07).

CONCLUSIONS

Cross-sectional association cannot indicate direction of trend or predict the future. Predicting metabolic health from anthropometric measures in prepubertal children requires longitudinal data, tracking variables from childhood into adulthood. Until the data set reaches adulthood, it is probably not safe to make recommendations on which children to 'target' or whether early intervention would be of benefit.