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/height(1) (WHtR(a)), and using two published age and sex-specific exponents for height (WHtR(b)) (1) (WHtR(c)) (2), and compared with various DXA indexes of body composition using receiver operating curve analysis. 15% of males and 17% of females had a WHtR(a) ≥0.5, with corresponding figures of 8% and 27% for WHtR(b), and 23% and 17% for WHtR(c). WHtR(a) was significantly different from WHtR(b) (males only, P < 0.001) but not WHtR(c) (P = 0.121). Areas under the receiver operating curve (AUC) for WHtR(a) were significantly higher than AUCs for WHtR(b) or WHtR(c) in relation to DXA-measured body composition (AUCs ≥0.89 for WHtR(a) compared with AUCs of 0.71-0.84 for WHtR(b) and WHtR(c)). Simply dividing waist circumference by height (WHtR(a)) 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.

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 > or =20 years and females > or =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.

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.

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 association between obesity and asthma: interactions between systemic and airway inflammation.

RATIONALE: Both obesity and asthma are common conditions, and both are characterized by the presence of inflammation. Animal studies suggest that the development of airway hyperresponsiveness with antigen challenge is exaggerated with obesity. However, clear evidence for either an additive or a synergistic pathologic interaction between obesity and asthma is lacking in humans. OBJECTIVES: To identify whether an interaction between systemic and local inflammation occurs in obese subjects with asthma in a controlled observational study. METHODS: We studied 79 women: obese patients with asthma (n = 20), normal-weight patients with asthma (n = 19), obese patients without asthma (n = 20), and normal-weight patients without asthma (n = 20). After corticosteroid withdrawal, between-group differences in spirometric values, lung volumes, exhaled nitric oxide, induced sputum cell counts, and biomarkers of inflammation in sputum supernatant and blood were measured, and interactions explored. MEASUREMENTS AND MAIN RESULTS: Markers of systemic inflammation were increased with obesity, and Th2 cytokines were increased with asthma, but no important interactions were identified. Obesity adversely affected lung function with increases in functional residual capacity and residual volume in obese but not normal-weight patients with asthma, with a significant obesity by asthma interaction. CONCLUSIONS: The link between obesity and asthma is unlikely to be explained by enhancement of the "classical" forms of airway inflammation resulting from the systemic inflammatory effects of obesity itself. Other mechanisms, possibly related to innate immunity, may explain the relationship between obesity and asthma.

Relationship of total body fat mass to bone area in New Zealand five-year-olds.

Fat mass was recently shown to be a positive determinant of bone mass and size independently of lean mass in a birth cohort of British 9-year-olds. The present study was undertaken to investigate whether similar relationships are evident in younger, preschool children. Height and weight were measured, and a total-body dual-energy X-ray absorptiometric scan was performed on 194 preschool New Zealand children (81 girls, 113 boys) participating in the Dunedin birth cohort Family, Lifestyle, Activity, Movement, and Eating (FLAME) study close to their fifth birthday. Relationships of total-body fat mass and lean mass to total-body-less-head (TBLH) bone area and TBLH bone mineral content (BMC) were evaluated using linear regression. Girls had higher mean fat mass (3.9 vs. 3.2 kg) and lower lean mass (14.5 vs. 15.2 kg) than boys (P < 0.001), but their heights, weights, and TBLH bone area were similar. Although a given weight of lean tissue was associated with greater increases in TBLH area than a given weight of fat tissue, our results show that fat mass was an independent predictor of TBLH bone area (R (2 )= 0.79, P < 0.001) and TBLH BMC (R (2) = 0.74, P < 0.001) in data adjusted for socioeconomic status, ethnic group, lean mass, and height. We conclude that increased fat mass is associated with outward expansion of the TBLH skeletal envelope (wider bones) independently of height and lean mass in very young children.

Body mass index status is effective in identifying metabolic syndrome components and insulin resistance in Pacific Island teenagers living in New Zealand.

Although adults of Pacific ethnicity living in New Zealand have more than double the prevalence of diabetes and cardiovascular disease than the general population, little is known regarding the presence of risk factors for these disorders among young Pacific Islanders. The study aim was to examine relationships between body composition, glucose and lipid metabolism, and components of the metabolic syndrome (MS) in a community sample of Pacific Island (PI) teenagers living in Dunedin. Anthropometry, body composition (dual-energy x-ray absorptiometry), glucose and lipid metabolism, insulin resistance (homeostasis model assessment [HOMA2], McAuley index), and components of MS were assessed in 80 PI teenagers (aged 15-18 years). Results showed that 6 participants had full MS, 2 had high fasting blood glucose values (>7.0 mmol/L), 55 had high adiposity, and 21 had insulin resistance. Assessment of the components of MS by body mass index (BMI) status showed that obese participants (n = 29) had a high prevalence (86.2% had one or more component), whereas only 10.5% of those with healthy BMI status (n = 19) had any MS component. Elevated fat mass had substantial effects on fasting insulin values, HOMA2, and the McAuley index because in data adjusted for age, sex, and lean mass, a 10% greater fat mass was associated with a 4.7% increase in fasting insulin, a 5.3% rise in HOMA2, and a 2.3% decrease in the McAuley index. Our results suggest that the antecedents of cardiovascular disease and type 2 diabetes mellitus occur frequently in young Pacific Islanders having high adiposity. We conclude that community studies of PI adolescents should focus on assessing risk factors whenever BMI values are high.

Ethnic differences in extreme obesity.

A nationwide representative survey of New Zealand schoolchildren showed a 2.7% incidence of extreme obesity (versus 4% in the United States) but revealed worrying ethnic differences in prevalence. Prevalence percentages (95% CI) were 0.8 (0.4 to 1.9), 5.1 (3.6 to 7.1), and 10.9 (8.9 to 13.3) in New Zealand European, Maori, and Pacific Island groups, respectively. These findings warrant remedial action.

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. RESEARCH METHODS AND PROCEDURES: Weights, heights, BMI, and waist girths of New Zealand children ages 3 to 8 years were determined. Fat mass, fat percentage, and lean mass were measured by DXA (n = 96). Parents classified child weight status as underweight, normal-weight, slightly overweight, or overweight. Centers for Disease Control and Prevention 2000 percentiles of BMI were used. RESULTS: Parents underestimated child weight status. Despite having 83% more fat mass than children with BMI values below the 85th percentile, only 7 of 31 children with BMI values at or above the 85th percentile were rated as slightly overweight or overweight. In the whole sample, participants whose weight status was underestimated by parents (40 of the 96 children) had l9% less fat mass but similar lean mass as children whose weight status was correctly classified. However, children of obese and non-obese parents did not differ in body composition or anthropometry, and obese parents did not underestimate child weight more than non-obese parents. DISCUSSION: Because parents underestimate child weight, but BMI values at or above the 85th percentile identify high body fat well, advising parents of the BMI status of their children should improve strategies to prevent excessive fat gain in young 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.

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

UNLABELLED: 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. INTRODUCTION: Although many apparently healthy children fracture their forearms repeatedly during growth, no previous studies of their bone health and body composition have been undertaken. Nor has the prevalence of established risk factors for fracture in such a population been assessed. MATERIALS AND METHODS: Ninety children and adolescents (47 girls and 43 boys) 5-19 years of age, who had experienced at least two fractures of the forearm, were studied. Bone size and mineralization were assessed using DXA at the ultradistal radius, one-third radius, neck of femur, hip trochanter, lumbar spine, and total body. Total body lean mass and fat mass were also determined. The prevalence of six risk factors for fracture were also examined, and their influence on ultradistal BMC Z scores was assessed. RESULTS: Participants experienced 295 fractures (74.9% forearm). Children with an early age of first fracture had higher rates of fracture per l00 years of exposure than those fracturing later. Four risk factors for fracture were over-represented in observed versus expected percentages: early age of first fracture (27.7% versus 11.3%), adverse symptoms to cow milk (22.2% versus 6.7%), low dietary calcium intake (20% versus 4.5%), and overweight (33.3% versus 15.5%). However, physical activity levels were similar to the reference population. Z scores for BMC and BMD were reduced, particularly at the ultradistal radius, whereas Z scores for weight, body mass index, fat mass, and body fat percentage were increased. Mean (SD) BMC Z scores were lowest at the ultradistal radius, -0.66 (1.22), where symptoms to milk were associated with reduced values (p < 0.009) and overweight with increased values (p < 0.003). CONCLUSIONS: Our results suggest site-specific weakness and high body weight contribute to fracture risk in children and adolescents who fracture their forearms repeatedly. These findings are consonant with work showing adult Colles fractures increase as ultradistal radius BMD falls and with evidence that overweight children and adolescents are fracture prone.

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

PURPOSE OF REVIEW: Improving 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 FINDINGS: Investigations 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. SUMMARY: Future 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.

First fracture is associated with increased risk of new fractures during growth.

Prior fracture was associated with increased risk of new fracture in 601 members of a cohort studied between birth and l8 years. Hazard ratios for new fracture in data adjusted for age and sex were l.90 (95%CI l.51-2.39) after first fracture and 3.04 (95% CI 2.23-4.15) after second fracture.

Dietary factors are not associated with high levels of obesity in New Zealand Pacific preschool children.

Pacific children living in New Zealand (NZ) are prone to excessive weight gain. In this study, we assessed the anthropometric status of 2- to 5-y-old Pacific children (n = 60) in relation to their macronutrient intakes. Measurements of height (n = 56), weight (n = 60), midarm circumference, and triceps skinfold thickness (n = 58), and 2-d weighed food records (n = 60) and demographic data were collected. Z-score results (mean +/- SD) showed that these children were tall (0.61 +/- 1.1) and heavy (1.67 +/- 1.1) for their age, and had high arm-muscle-area-for-height (geometric mean, 2.05). Over 64 and 45% of children were classified as overweight (including obesity) and obese, respectively. The percentage of energy contributed by fat in their diets met recommendations. In contrast, the percentage of energy contributed by sugar was high. The macronutrient intakes of children classified as obese (n = 32) compared with non-obese (n = 24) did not differ; however, their adjusted energy intakes were higher [5.79 (1.4) vs. 4.97 (1.4) MJ/d; P = 0.01]. Overweight and obesity were very common among very young NZ Pacific children, although the dietary etiology was not elucidated. These results emphasize the urgent need for obesity prevention for NZ Pacific children that begins early in life to avoid a future public health crisis.

Children who avoid drinking cow's milk are at increased risk for prepubertal bone fractures.

The full fracture histories of 50 children (30 girls and 20 boys, age range 3 to 13 years) who had avoided drinking cow's milk for prolonged periods were compared with those in a birth cohort of more than 1,000 children from the same city. Children who avoided milk did not use calcium-rich food substitutes appropriately and had low dietary calcium intakes and low bone mineral density values. Many were overweight (22 of 50). Significantly more of the children who avoided milk reported fractures (16 observed vs 6 expected, chi(2)=31.0, P<.001, df=5). They also experienced more total fractures than the birth cohort population (22 observed vs 8 expected, chi(2)=33.6, P<.001, df=5). All of the fractures occurred before puberty, the majority (18 of 22) being associated with only slight trauma. Forearm fractures were especially common (12 fractures). We conclude that young children avoiding milk are prone to fracture.

High levels of childhood obesity observed among 3- to 7-year-old New Zealand Pacific children is a public health concern.

This cross-sectional, community-based survey was designed to assess attained growth and body composition of 3- to 7-y-old Pacific children (n = 21 boys and 20 girls) living in Dunedin, New Zealand, and to examine nondietary factors associated with the percentage of body fat. Fat mass, lean tissue mass and the percentage of body fat were measured using dual energy X-ray absorptiometry. One trained anthropometrist also measured height, weight, skinfolds (triceps, subscapular) and circumferences (mid-upper arm, chest, waist, calf). Compared with the National Center for Health Statistics and National Health and Examination Surveys I and II reference data, these Pacific children were tall and heavy for their age with high arm-muscle-area-for-height. Median (quartiles) Z-scores for height and BMI-for-age and arm-muscle-area-for-height were 1.33 (0.60, 2.15), 1.20 (0.74, 4.43) and 1.09 (0.63, 1.85), respectively. Their median (quartile) percentage of body fat was 21.8% (15.0, 35.5) of which 38.5% was located in the trunk. The estimated percentage of children classified as obese ranged from 34 to 49% depending on the criterion used. Over 60% of the children had levels of trunk fat above 1 SD of reported age- and sex-specific Z-scores for New Zealand children. The nondietary factors examined (hours of television viewing and hours playing organized sports, as reported by parents) were not associated with variations in the percentage of body fat, after adjusting for age, sex and birth weight. These extremely high levels of obesity and truncal fat among very young New Zealand children will have major public health implications as these children age.

Selenium supplements do not increase plasma total homocysteine concentrations in men and women.

Studies in rats indicate that plasma total homocysteine (tHcy) is decreased in selenium deficiency and increases with selenium supplementation. The aim of this study was to determine the effect of selenium supplements on plasma tHcy concentrations in a population that has suboptimal selenium status. Subjects from Dunedin, New Zealand (n = 189) were randomly assigned to receive a supplement containing 200 micro g selenium or placebo for 20 wk. At baseline, 67% (n = 112) of the participants had plasma selenium concentrations < 1.2 micro mol/L, a concentration believed to be that necessary for full glutathione peroxidase (Gpx) activity. At 20 wk, plasma selenium concentration and Gpx activity increased in the selenium group by 1.2 micro mol/L [95% confidence interval (CI): 1.1, 1.3] and 5.1 nkat/g protein (3.7, 6.5), respectively, changes that were significantly greater than the changes in the placebo group (P < 0.001). At 20 wk, mean changes in plasma tHcy concentrations were 0.1 micro mol/L (95% CI: -0.4, 0.5) and -0.2 micro mol/L (-0.7, 0.3) in the supplemented and placebo groups, respectively, compared to baseline. There was no difference in the mean changes in plasma tHcy between the supplemented and placebo groups (P = 0.54). These results suggest that selenium supplementation does not influence plasma tHcy concentrations in healthy populations in developed countries, whose selenium status is characterized by lower plasma selenium concentrations.