Andrea M. Grant

Bone and body composition of children and adolescents with repeated forearm fractures.

DXA measurements in 90 children and adolescents with repeated forearm fractures showed reduced ultradistal radius BMC and BMD values and elevated adiposity, suggesting site‐specific bone weakness and high body weight increase fracture risk. Symptoms to cow milk, low calcium intakes, early age of first fracture, and overweight were over‐represented in the sample.

Early adiposity rebound: review of papers linking this to subsequent obesity in children and adults.

Purpose of reviewImproving our understanding of factors driving fat gain in young children should increase our ability to manage the rising problem of obesity. Accordingly, studies associating timing of adiposity rebound with later obesity are reviewed. Recent findingsInvestigations in many countries have confirmed that early adiposity rebound increases risk of high blood pressure and obesity in young adults. The magnitude of the effect can be substantial (>3 body mass index units at 18–21 years) for those undergoing early (<5 years of age) compared with late (>7 years of age) rebound. Early rebound is also associated with impaired glucose tolerance and diabetes in adulthood. Because adiposity rebound is determined using serial measurements of body mass index, the actual changes in body composition occurring during this time are obscured. Recent data show that changing body mass index during adiposity rebound is due to higher than average deposition of weight rather than slowing of the rate of height gain. Moreover, this increased weight gain occurs because of rapid deposition of fat rather than lean tissue, with early rebounders gaining fat mass at almost three times the rate of late rebounders. SummaryFuture work is needed to identify reasons for early adiposity rebound. Because high physical activity and low inactivity are associated with lower body fat during the period of adiposity rebound, studies should be undertaken to see whether stepping up activity can slow fat gain, delay the onset of adiposity rebound and lower adult obesity.

Sex Differences in Regional Body Fat Distribution From Pre- to Postpuberty

Few large studies have evaluated the emergence of sexual dimorphism in fat distribution with appropriate adjustment for total body composition. The objective of this study was to determine the timing and magnitude of sex differences in regional adiposity from early childhood to young adulthood. Regional fat distribution was measured using dual‐energy X‐ray absorptiometry (trunk and extremity fat using automatic default regions and waist and hip fat using manual analysis) in 1,009 predominantly white participants aged 5–29 years. Subjects were divided into pre (Tanner stage 1), early (Tanner stages 2–3), late (Tanner stages 4–5), and post (males ≥20 years and females ≥18 years) pubertal groups. Sexual dimorphism in trunk fat (adjusted for extremity fat) was not apparent until late puberty, when females exhibited 17% less (P < 0.001) trunk fat than males. By contrast, sex differences in waist fat (adjusted for hip fat) were apparent at each stage of puberty, the effect being magnified with age, with prepubertal girls having 5% less (P = 0.027) and adult women having 48% less (P < 0.0001) waist fat than males. Girls had considerably more peripheral fat whether measured as extremity or hip fat at each stage. Sex differences in regional adiposity were significantly greater in young adults than in late adolescence. Exclusion of overweight participants did not materially affect the estimates. Sexual dimorphism in fat patterning is apparent even prepubertally with girls having less waist and more hip fat than boys. The magnitude of the sex difference is amplified with maturation, and particularly from late puberty to early adulthood.

The effect of adiposity measured by dual-energy X-ray absorptiometry on lung function

Respiratory function is impaired in obesity but there are limitations with body mass index and skin-fold thickness in assessing this effect. The present authors hypothesised that the regional distribution of body fat and lean mass, as measured by dual-energy X-ray absorptiometry (DXA), might be more informative than conventional measurements of total body fat. In total, 107 subjects (55 female, 51.4%) aged 20–50 yrs with no respiratory disease were recruited. Respiratory function tests, anthropometric measurements and a DXA scan were performed. Partial correlation and linear regression analyses were used to explore the effect of adiposity and lean body mass on respiratory function. The majority of respiratory function parameters were significantly correlated with DXA and non-DXA measurements of body fat. Neither thoracic nor abdominal fat had a greater effect. There were some differences in the effect of adiposity between the sexes. Respiratory function was negatively associated with lean body mass in females but positively associated in males. This disappeared after adjustment in females but remained in males. The effects of thoracic and abdominal body fat on respiratory function are comparable but cannot be separated from one another.

Waist circumference as a measure of trunk fat mass in children aged 3 to 5 years.

OBJECTIVE The increasing prevalence of obesity in young children emphasises the need for accurate measures of total and regional fat at this age. Thus the aim of this study was to evaluate the ability of waist circumference, waist-to-height ratio (WHtR) and the conicity index (CI) to discriminate between children with low and high levels of trunk fat mass. METHODS Trunk fat mass was measured by dual-energy x-ray absorptiometry (DXA) in 301 predominantly Caucasian children (150 girls) aged 3-5 years. High trunk fat was defined as an internal z-score of > or =+1. Receiver-operating characteristic (ROC) curves and the areas under each curve (AUC) were constructed to compare the relative ability of waist circumference, WHtR and CI to identify children with low and high trunk fat mass. RESULTS Girls had more truncal fat than boys (P<0.001). AUCs indicated that waist circumference correctly discriminated between children with low and high trunk fat mass 87% (for girls) to 90% (for boys) of the time. Waist circumference performed better than WHtR (AUCs: 0.79 in girls and 0.81 in boys; P=0.164 and P=0.011, respectively) and the CI (AUCs: 0.53 in girls and 0.65 in boys, P<0.0001). A z-score of 0.55 correctly identified 79% of girls and 81% of boys with high trunk fat mass, and 82% of girls and 84% of boys with low trunk fat mass. Suggested waist circumference cut-offs for each half-year of age in both sexes are reported. CONCLUSION Waist circumference performs reasonably well as an indicator of high trunk fat mass in preschool-aged children.

The effect of selenium on thyroid status in a population with marginal selenium and iodine status

The effects of Se on thyroid metabolism in a New Zealand population are investigated, including (a) the relationship between Se and thyroid status, and (b) the effect of Se supplementation on thyroid status. The data used come from two cross-sectional studies of Se, I, thyroid hormones and thyroid volume (studies 1 and 4), and three Se intervention studies in which thyroid hormones, Se and glutathione peroxidase (GPx) activities were measured (studies 2, 3 and 5). There were no significant correlations between Se status and measures of thyroid status after controlling for sex at baseline or after supplementation in any of the studies. When data from study 4 were divided into two groups according to plasma Se, plasma thyroxine (T4) was lower in males with higher plasma Se levels (P=0.009). Se supplementation increased plasma Se and GPx activity, but produced only small changes in plasma T4 and triiodothyronine (T3):T4 ratio. In study 2, there was a significant reduction in plasma T4 (P=0.0045). In studies 3 and 5 there were small decreases in plasma T4 and a small increase in the T3:T4 ratio, which were not significantly different from placebo groups. Lack of significant associations between plasma Se and thyroid status, and only small changes in T4 suggest that Se status in New Zealand is close to adequate for the optimal function of deiodinases. Adequate plasma Se may be approximately 0.82-0.90 micromol/l, compared with 1.00-1.14 micromol/l for maximal GPx activities.

DXA Measurements Confirm that Parental Perceptions of Elevated Adiposity in Young Children are Poor

Objective: To compare parental assessments of child body weight status with BMI measurements and determine whether children who are incorrectly classified differ in body composition from those whose parents correctly rate child weight. Also to ascertain whether children of obese parents differ from those of non‐obese parents in actual or perceived body weight.

Predictive Ability of Waist‐to‐Height in Relation to Adiposity in Children Is Not Improved With Age and Sex‐Specific Values

A waist‐to‐height ratio (WHtR) ≥0.5 indicates increased health risk in children and adults. However, because of residual correlation between WHtR and height in children, dividing waist circumference by height to the power of one may be insufficient to correctly adjust for height during growth. This study aimed to determine whether age and sex‐specific exponents which properly adjust for height affect the predictive ability of WHtR to correctly discriminate between children with differing fat distribution. Total and regional body fat was measured by dual‐energy X‐ray absorptiometry (DXA) in 778 (49% male) children and adolescents. WHtR was calculated as waist/height1 (WHtRa), and using two published age and sex‐specific exponents for height (WHtRb) ( 1 ) (WHtRc) ( 2 ), and compared with various DXA indexes of body composition using receiver operating curve analysis. 15% of males and 17% of females had a WHtRa ≥0.5, with corresponding figures of 8% and 27% for WHtRb, and 23% and 17% for WHtRc. WHtRa was significantly different from WHtRb (males only, P < 0.001) but not WHtRc (P = 0.121). Areas under the receiver operating curve (AUC) for WHtRa were significantly higher than AUCs for WHtRb or WHtRc in relation to DXA‐measured body composition (AUCs ≥0.89 for WHtRa compared with AUCs of 0.71–0.84 for WHtRb and WHtRc). Simply dividing waist circumference by height (WHtRa) correctly discriminates between children and adolescents with low and high levels of total and central fat at least 90% of the time. Keeping your waist circumference to less than half your height provides an effective screening index of body composition during growth.

Relationships of appendicular LMI and total body LMI to bone mass and physical activity levels in a birth cohort of New Zealand five-year olds.

The present study was undertaken to determine whether children with lower bone mass display lower muscle mass for their height than those with high bone mineral content (BMC) and whether appendicular lean mass (bone-free lean mass in arms plus legs) is associated with physical activity and/or BMC in preschool children. 158 children (59% male) from a New Zealand cohort born in 2001-2002 were studied close to their fifth birthday. Body composition was measured by dual energy X-ray absorptiometry (Lunar DPX-L). Lean mass index (LMI) was calculated as lean mass (kg) divided by height in metres squared. Physical activity was assessed objectively by accelerometry (Actical Mini-Mitter). Girls and boys had similar heights, weights and daily accelerometry counts but boys had lower fat mass, and higher lean mass and total body BMC than the girls (P<0.00l). In both sexes children with greater quantities of total and regional lean mass and higher LMI values had significantly higher bone mass. Appendicular LMI was more strongly associated with BMC than LMI. Accelerometry counts showed no associations with height but were positively associated with lean mass (r=0.23, P<0.03), appendicular LMI (r=0.25 P<0.01), total body BMC (r=0.24, P<0.02) and total body less head BMC (r=0.27 P<0.009) in the boys, but not in the girls. Greater time spent in more intense physical activity was also associated with higher appendicular lean mass and TBLH BMC only in the boys. We conclude that children with lower BMC values display not only lower lean mass but also lower total and appendicular lean mass for their height, than those with higher BMC values. The sex differences in associations of accelerometry counts to lean mass and BMC have been noted by others and require further investigation.

Do young New Zealand Pacific Island and European children differ in bone size or bone mineral

Although Pacific Island adults have been shown to have larger bones and greater bone mineral density than caucasians, no previous studies have been undertaken to determine whether differences are present in prepubertal children. Forty-one Pacific Island children (both parents of Pacific Island descent) and 38 European children, aged 3 to 7 years, living in New Zealand were studied. Heights and weights were determined by simple anthropometry and body mass index (BMI, kg/m2) was calculated. Body composition, bone size, and bone mineral content (BMC, g) were measured by dual energy X-ray absorptiometry (DXA) of the total body and the non-dominant forearm. Compared to European children, in data adjusted for age and gender, Pacific Island children had significantly greater (P < 0.05) BMC in the total body (12%), the ultradistal radius (16%), and the 33% radius (8%), and also greater total body bone area (10%). Bone mineral density (BMD, g/cm2) was higher only at the ultradistal radius (11%). However, after adjustment for body weight, in particular lean mass, no differences were seen between Pacific Island and European children in any bone measure. The larger bone area and BMC of young Pacific Island children can be explained by their greater height and weight. Therefore, this study has shown that prepubertal Pacific Island children do not have greater bone size or BMC for their weight.