A changing pattern of childhood BMI growth during the 20th century: 70 y of data from the Fels Longitudinal Study

Genetically inferred birthweight, height, and puberty timing and risk of osteosarcoma

INTRODUCTION

Several studies have linked increased risk of osteosarcoma with tall stature, high birthweight, and early puberty, although evidence is inconsistent. We used genetic risk scores (GRS) based on established genetic loci for these traits and evaluated associations between genetically inferred birthweight, height, and puberty timing with osteosarcoma.

METHODS

Using genotype data from two genome-wide association studies, totaling 1039 cases and 2923 controls of European ancestry, association analyses were conducted using logistic regression for each study and meta-analyzed to estimate pooled odds ratios (ORs) and 95% confidence intervals (CIs). Subgroup analyses were conducted by case diagnosis age, metastasis status, tumor location, tumor histology, and presence of a known pathogenic variant in a cancer susceptibility gene.

RESULTS

Genetically inferred higher birthweight was associated with an increased risk of osteosarcoma (OR =1.59, 95% CI 1.07-2.38, P = 0.02). This association was strongest in cases without metastatic disease (OR =2.46, 95% CI 1.44-4.19, P = 9.5 ×10-04). Although there was no overall association between osteosarcoma and genetically inferred taller stature (OR=1.06, 95% CI 0.96-1.17, P = 0.28), the GRS for taller stature was associated with an increased risk of osteosarcoma in 154 cases with a known pathogenic cancer susceptibility gene variant (OR=1.29, 95% CI 1.03-1.63, P = 0.03). There were no significant associations between the GRS for puberty timing and osteosarcoma.

CONCLUSION

A genetic propensity to higher birthweight was associated with increased osteosarcoma risk, suggesting that shared genetic factors or biological pathways that affect birthweight may contribute to osteosarcoma pathogenesis.

The associations of maternal and paternal obesity with latent patterns of offspring BMI development between 7 and 17 years of age: pooled analyses of cohorts born in 1958 and 2001 in the United Kingdom

OBJECTIVE

We aimed to 1) describe how the UK obesity epidemic reflects a change over time in the proportion of the population demonstrating adverse latent patterns of BMI development and 2) investigate the potential roles of maternal and paternal BMI in this secular process.

METHODS

We used serial BMI data between 7 and 17 years of age from 13220 boys and 12711 girls. Half the sample was born in 1958 and half in 2001. Sex-specific growth mixture models were developed. The relationships of maternal and paternal BMI and weight status with class membership were estimated using the 3-step BCH approach, with covariate adjustment.

RESULTS

The selected models had five classes. For each sex, in addition to the two largest normal weight classes, there were "normal weight increasing to overweight" (17% of boys and 20% of girls), "overweight increasing to obesity" (8% and 6%), and "overweight decreasing to normal weight" (3% and 6%) classes. More than 1-in-10 children from the 2001 birth cohort were in the "overweight increasing to obesity" class, compared to less than 1-in-30 from the 1958 birth cohort. Approximately 75% of the mothers and fathers of this class had overweight or obesity. When considered together, both maternal and paternal BMI were associated with latent class membership, with evidence of negative departure from additivity (i.e., the combined effect of maternal and paternal BMI was smaller than the sum of the individual effects). The odds of a girl belonging to the "overweight increasing to obesity" class (compared to the largest normal weight class) was 13.11 (8.74, 19.66) times higher if both parents had overweight or obesity (compared to both parents having normal weight); the equivalent estimate for boys was 9.01 (6.37, 12.75).

CONCLUSIONS

The increase in obesity rates in the UK over more than 40 years has been partly driven by the growth of a sub-population demonstrating excess BMI gain during adolescence. Our results implicate both maternal and paternal BMI as correlates of this secular process.

Quadriceps muscle volume positively contributes to ACL volume

Females have smaller anterior cruciate ligaments (ACLs) than males and smaller ACLs have been associated with a greater risk of ACL injury. Overall body dimensions do not adequately explain these sex differences. This study examined the extent to which quadriceps muscle volume (VOL_QUAD ) positively predicts ACL volume (VOL_ACL ) once sex and other body dimensions were accounted for. Physically active males (N = 10) and females (N = 10) were measured for height, weight, and body mass index (BMI). Three-Tesla magnetic resonance images of their dominant and nondominant thigh and knee were then obtained to measure VOL_ACL , quadriceps, and hamstring muscle volumes, femoral notch width, and femoral notch width index. Separate three-step regressions estimated associations between VOL_QUAD and VOL_ACL (third step), after controlling for sex (first step) and one body dimension (second step). When controlling for sex and sex plus BMI, VOL_HAM , notch width, or notch width index, VOL_QUAD consistently exhibited a positive association with VOL_ACL in the dominant leg, nondominant leg, and leg-averaged models (p < 0.05). Findings were inconsistent when controlling for sex and height (p = 0.038-0.102). Once VOL_QUAD was included, only notch width and notch width index retained a statistically significant individual association with VOL_ACL (p < 0.01). Statement of Clinical Significance: The positive association between VOL_QUAD and VOL_ACL suggests ACL size may in part be modifiable. Future studies are needed to determine the extent to which an appropriate training stimulus (focused on optimizing overall lower extremity muscle mass development) can positively impact ACL size and structure in young females.

Adiposity rebound and cardiometabolic health in childhood: results from the Generation XXI birth cohort

BACKGROUND

We aimed to evaluate the association of adiposity rebound (AR) timing on cardiometabolic health in childhood.

METHODS

Participants were part of the Generation XXI birth cohort, enrolled in 2005/2006 in Porto. All measurements of the child's weight and height performed by health professionals as part of routine healthcare were collected. Individual body mass index (BMI) curves were fitted for 3372 children, using mixed-effects models with smooth spline functions for age and random effects. The AR was categorized into very early (<42 months), early (42-59 months), normal (60-83 months) and late (≥84 months). At age 10 years, cardiometabolic traits were assessed and age- and sex-specific z-scores were generated. Adjusted regression coefficients and 95% confidence intervals [β (95% CI)] were computed.

RESULTS

The mean age at AR was 61.9 months (standard deviations 15.7). Compared with children with normal AR, children with very early or early AR had higher z-scores for BMI [β = 0.40 (95% CI: 0.28; 0.53); β = 0.21 (95% CI: 0.12; 0.30)], waist circumference [β = 0.33 (95% CI: 0.23; 0.43); β = 0.18 (95% CI: 0.10; 0.25)], waist-height ratio [β = 0.34 (95% CI: 0.24; 0.44); β = 0.14 (95% CI: 0.07; 0.22)], fat mass index [β = 0.24 (95% CI: 0.15; 0.33); β = 0.14 (95% CI: 0.08; 0.21)], fat-free mass index [β = 0.25 (95% CI: 0.14; 0.35); β = 0.11 (95% CI: 0.03; 0.19)], systolic blood pressure [β = 0.10 (95% CI: 0.01; 0.20); β = 0.08 (95% CI: 0.01; 0.15)], insulin [β = 0.16 (95% CI: 0.04; 0.29); β = 0.10 (95% CI: 0.01; 0.19)], HOMA-IR [β = 0.17 (95% CI: 0.04; 0.29); β = 0.10 (95% CI: 0.03; 0.19)] and C-reactive protein [β = 0.14 (95% CI: 0.02; 0.26); β = 0.10 (95% CI: 0.01; 0.19)]. Children with very early AR also had worse levels of diastolic blood pressure [β = 0.09 (95% CI: 0.02; 0.16)], triglycerides [β = 0.21 (95% CI: 0.08; 0.34)] and high-density lipoprotein cholesterol [β=-0.18 (95% CI: -0.31; -0.04)]. When analysed continuously, each additional month of age at the AR was associated with healthier cardiometabolic traits.

CONCLUSION

The earlier the AR, the worse the cardiometabolic health in late childhood, which was consistently shown across a wide range of outcomes and in the categorical and continuous approach.

Pre-Birth and Early-Life Factors Associated With the Timing of Adiposity Peak and Rebound: A Large Population-Based Longitudinal Study

Background: The late occurrence of adiposity peak (AP) and the early occurrence of adiposity rebound (AR) are considered the earliest indicators for obesity and its related health conditions later in life. However, there is still limited information for their upstream factors. Therefore, in this study, we aimed to identify the parental and child factors associated with the timing of AP and AR in the early stage of life. Methods: This is a population-based longitudinal study conducted in Shanghai, China. The BMI data of children born between September 2010 and October 2013 were followed from birth to 80 months. Subject-specific body mass index trajectories were fitted by non-linear mixed-effect models with natural cubic spline functions, and the individual's age at AP and AR was estimated. The generalized linear regression models were applied to identify the upstream factors of late occurrence of AP and early occurrence AR. Results: For 7,292 children with estimated AP, boys were less likely to have a late AP [adjusted risk ratio (RR) = 0.83, 95% confidence interval (CI): 0.77-0.90, p < 0.001], but preterm born children had a higher risk of a late AP (adjusted RR = 1.25, 95% CI: 1.07-1.47, p < 0.01). For 10,985 children with estimated AR, children with breastfeeding longer than 4 months were less likely to have an early AR (adjusted RR = 0.80, 95% CI: 0.73-0.87, p < 0.001), but children who were born to advanced-age mothers and who were born small for gestational age had a higher risk of having an early AR (adjusted RR = 1.21, 95% CI: 1.07-1.36, p < 0.01; adjusted RR = 1.20, 95% CI: 1.04-1.39, p = 0.01). Conclusions: Modifiable pre-birth or early-life factors associated with the timing of AP or AR were found. Our findings may help develop prevention and intervention strategies at the earliest stage of life to control later obesity and the health conditions and diseases linked to it.

Body mass index trajectories and adiposity rebound during the first 6 years in Korean children: Based on the National Health Information Database, 2008-2015

PURPOSE

We analyzed the nationwide longitudinal data to explore body mass index (BMI) growth trajectories and the time of adiposity rebound (AR).

METHODS

Personal data of 84,005 subjects born between 2008 and 2012 were obtained from infant health check-ups which were performed at 5, 11, 21, 33, 45, 57, and 69 months. BMI trajectories of each subject were made according to sex and the timing of AR, which was defined as the lowest BMI occurred. Subjects were divided according to birth weight and AR timing as follows: very low birth weight (VLBW), 0.5 kg ≤ Bwt ≤ 1.5 kg; low birth weight (LBW), 1.5 kg < Bwt ≤ 2.5 kg; non-LBW, 2.5 kg < Bwt ≤ 5.0 kg; very early AR, before 45 months; early AR, at 57 months; and moderate-to-late AR, not until 69 months.

MAIN RESULTS

Median time point of minimum BMI was 45 months, and the prevalence rates of very early, early, and moderate-to-late AR were 63.0%, 16.6%, and 20.4%, respectively. BMI at the age of 57 months showed a strong correlation with AR timing after controlling for birth weight (P < 0.001). Sugar-sweetened beverage intake at 21 months (P = 0.02) and no-exercise habit at 57 months (P < 0.001) showed correlations with early AR. When VLBW and LBW subjects were analyzed, BMI at 57 months and breastfeeding at 11 months were correlated with rapid weight gain during the first 5 months (both P < 0.001).

CONCLUSIONS

Based on this first longitudinal study, the majority of children showed AR before 57 months and the degree of obesity at the age of 57 months had a close correlation with early AR or rapid weight gain during infancy.

Maternal and infant prediction of the child BMI trajectories; studies across two generations of Northern Finland birth cohorts

BACKGROUND/OBJECTIVE

Children BMI is a longitudinal phenotype, developing through interplays between genetic and environmental factors. Whilst childhood obesity is escalating, we require a better understanding of its early origins and variation across generations to prevent it.

SUBJECTS/METHODS

We designed a cross-cohort study including 12,040 Finnish children from the Northern Finland Birth Cohorts 1966 and 1986 (NFBC1966 and NFBC1986) born before or at the start of the obesity epidemic. We used group-based trajectory modelling to identify BMI trajectories from 2 to 20 years. We subsequently tested their associations with early determinants (mother and child) and the possible difference between generations, adjusted for relevant biological and socioeconomic confounders.

RESULTS

We identified four BMI trajectories, 'stable-low' (34.8%), 'normal' (44.0%), 'stable-high' (17.5%) and 'early-increase' (3.7%). The 'early-increase' trajectory represented the highest risk for obesity. We analysed a dose-response association of maternal pre-pregnancy BMI and smoking with BMI trajectories. The directions of effect were consistent across generations and the effect sizes tended to increase from earlier generation to later. Respectively for NFBC1966 and NFBC1986, the adjusted risk ratios of being in the early-increase group were 1.08 (1.06-1.10) and 1.12 (1.09-1.15) per unit of pre-pregnancy BMI and 1.44 (1.05-1.96) and 1.48 (1.17-1.87) in offspring of smoking mothers compared to non-smokers. We observed similar relations with infant factors including birthweight for gestational age and peak weight velocity. In contrast, the age at adiposity peak in infancy was associated with the BMI trajectories in NFBC1966 but did not replicate in NFBC1986.

CONCLUSIONS

Exposures to adverse maternal predictors were associated with a higher risk obesity trajectory and were consistent across generations. However, we found a discordant association for the timing of adiposity peak over a 20-year period. This suggests the role of residual environmental factors, such as nutrition, and warrants additional research to understand the underlying gene-environment interplay.

Childhood obesity: rapid weight gain in early childhood and subsequent cardiometabolic risk

Dynamic changes in body weight have long been recognized as important indicators of risk for human health. Many population-based observational studies have shown that rapid weight gain during infancy, including a catch-up growth phenomenon or adiposity rebound in early childhood, predisposes a person to the development of obesity, type 2 diabetes, and cardiovascular diseases later in life. However, a consensus has not been established regarding which period of weight gain contributes to future risks. This review evaluates recent evidence on the relationship between early rapid growth and future obesity and cardiometabolic risk, with a focus on the differential significance of rapid weight gain in infancy and early childhood. Although there is a need for attention to childhood growth during early infancy before 1 yr of age as it may be related to future obesity, emerging evidence strongly suggests that toddlers showing an increase in body mass index (BMI) before 3 yr of age, a period normally characterized by decreased BMI, are prone to developing later cardiometabolic risk.

Associations of childcare type, age at start, and intensity with body mass index trajectories from 10 to 42 years of age in the 1970 British Cohort Study

BACKGROUND

Attending childcare is related to greater childhood obesity risk, but there are few long-term follow-up studies. We aimed to examine the associations of childcare type, age at start, and intensity with body mass index body mass index (BMI) trajectories from ages 10 to 42 years.

METHODS

The sample comprised 8234 individuals in the 1970 British Cohort Study, who had data on childcare attendance (no, yes), type (formal, informal), age at start (4-5, 3-3.99, 0-2.99 years old), and intensity (1, 2, 3, 4-5 days/week) reported at age 5 years and 32 563 BMI observations. Multilevel linear spline models were used to estimate the association of each exposure with the sample-average BMI trajectory, with covariate adjustment. A combined age at start and intensity exposure was also examined.

RESULTS

Attending vs not attending and the type of childcare (none vs formal/informal) were not strongly related to BMI trajectories. Among participants who attended childcare 1 to 2 days a week, those who started when 3 to 3.99 years old had a 0.197 (-0.004, 0.399) kg/m² higher BMI at age 10 years than those who started when 4 to 5 years old, and those who started when 0 to 2.99 years old had a 0.289 (0.049, 0.529) kg/m² higher BMI. A similar dose-response pattern for intensity was observed when holding age at start constant. By age 42 years, individuals who started childcare at age 0 to 2.99 years and attended 3 to 5 days/week had a 1.356 kg/m² (0.637, 2.075) higher BMI than individuals who started at age 4 to 5 years and attended 1 to 2 days/week.

CONCLUSIONS

Children who start childcare earlier and/or attend more frequently may have greater long-term obesity risk.

Differences in the relationship of weight to height, and thus the meaning of BMI, according to age, sex, and birth year cohort

Background: Weight can be adjusted for height using the Benn parameter (kg/mB), where B is the power that minimises the correlation with height.Aim: To investigate how the Benn parameter changes across age (10-65 years) and time (1956-2015) and differs between sexes.Subjects and methods: The sample comprised 49,717 individuals born in 1946, 1958, 1970 or 2001. Cross-sectional estimates of the Benn parameter were produced and cohort differences at ages 10/11 and 42/43 years were examined using linear regression. Multilevel modelling was used to develop trajectories showing how the Benn parameter changed over age from childhood to mid-adulthood in the three older cohorts.Results: The Benn parameter was closest to 2 in childhood but consistently lower across adulthood, particularly in females and the most recent cohort. At ages 10/11 years, the Benn parameter was greater than 3 in both sexes in the 2001 cohort but between 2.2 and 2.7 in the three older cohorts. This difference was estimated to be +0.67 (0.53, 0.81) in males and +0.53 (0.38, 0.68) in females, compared to the 1946 cohort, and was driven by a much higher weight SD in the 2001 cohort. Conversely, at ages 42/43 years, the Benn parameter was lowest in the 1970 cohort due to a slightly lower weight-height correlation. This difference was estimated to be -0.12 (-0.34, 0.10) in males and -0.15 (-0.42, 0.13) in females, compared to the 1946 cohort.Conclusions: Changes over time in the obesogenic environment appear to have firstly reduced the Benn parameter due to a lowering of the weight-height correlation but secondly and more drastically increased the Benn parameter due to increasing weight variation.

Genome-wide association study reveals dynamic role of genetic variation in infant and early childhood growth

Infant and childhood growth are dynamic processes with large changes in BMI during development. By performing genome-wide association studies of BMI at 12 time points from birth to eight years (9286 children, 74,105 measurements) in the Norwegian Mother, Father, and Child Cohort Study, replicated in 5235 children, we identify a transient effect in the leptin receptor (LEPR) locus: no effect at birth, increasing effect in infancy, peaking at 6–12 months (rs2767486, P_6m = 2.0 × 10⁻²¹, β_6m = 0.16 sd-BMI), and little effect after age five. We identify a similar transient effect near the leptin gene (LEP), peaking at 1.5 years (rs10487505, P_1.5y = 1.3 × 10⁻⁸, β_1.5y = 0.079 sd-BMI). Both signals are protein quantitative trait loci for soluble-LEPR and LEP in plasma in adults independent from adult traits mapped to the respective genes, suggesting key roles of common variation in the leptin signaling pathway for healthy infant growth.

Changes in body mass index (BMI) during infancy and childhood follow a well-characterized pattern. Here, Helgeland et al. perform genome-wide association studies for BMI at 12 time points between birth and 8 years of age and find transient associations at the LEP and LEPR loci.

The adiposity rebound in the 21st century children: meaning for what?

With the increase in the prevalence of overweight and obesity worldwide, early adiposity rebound, which is known to have a strong association with obesity, has recently been a focus of research. Early adiposity rebound is conventionally known to have a close relationship with non-communicable diseases. However, novel insights into early adiposity rebound have implied an acceleration of growth and puberty, which is directly reflected in the trends in the timing of adiposity rebound, in the 21st century compared with in the past. Furthermore, the observation that lean mass changes rather than fat mass changes show a more similar pattern to body mass index trajectories is interesting. In this article, the later outcomes and risk factors of early adiposity rebound are briefly summarized, and the current trends in the timing of adiposity rebound and novel insights into its relationship with body composition are reviewed.

Body size trajectories and cardio-metabolic resilience to obesity

Individuals with obesity do not represent a single homogenous group in terms of cardio‐metabolic health prospects. The concept of metabolically healthy obesity is a crude way of capturing this heterogeneity and has resulted in a plethora of research linking to future outcomes to show that it is not a benign condition. By contrast, very few studies have looked back in time and modelled the life course processes and exposures that explain the heterogeneity in cardio‐metabolic health and morbidity and mortality risk among people with the same body mass index (BMI) (or waist circumference or percentage body fat). The aim of the Medical Research Council New Investigator Research Grant (MR/P023347/1) ‘Body size trajectories and cardio‐metabolic resilience to obesity in three United Kingdom birth cohorts’ is to reveal the body size trajectories, pubertal development patterns and other factors (e.g. early‐life adversity) that might attenuate the positive associations of adulthood obesity makers (e.g. BMI) with cardio‐metabolic disease risk factors and other outcomes, thereby providing some degree of protection against the adverse effects of obesity. This work builds on the Principle Investigator's previous research as part of the Cohort and Longitudinal Studies Enhancement Resources initiative and focuses on secondary data analysis in the nationally representative UK birth cohort studies (initiated in 1946, 1958 and 1970), which have life course body size and exposure data and a biomedical sweep in adulthood. The grant will provide novel evidence on the life course processes and exposures that lead to some people developing a cardio‐metabolic complication or disease or dying while other people with the same BMI do not. This paper details the grant's scientific rationale, research objectives and potential impact.

Improving Documentation of Pediatric Height, Weight, and Body Mass Index by Primary Care Providers

The regular documentation of anthropometric data in an electronic medical record (EMR) is one tracking method used by primary care providers to follow the growth trajectory and development of children in their health care practices. EMR reminders have been proposed as a method to increase recording of pediatric height and weight by primary care providers, leading to potentially better detection and management of children classified as overweight or obese. The aim of this pre-post study was to improve a Family Health Team's physician documentation of pediatric height and weight through the implementation of an EMR reminder alert tool. The documentation rate for children 4-7 years old in the 6 months before intervention was 36% of children seen. After implementation of EMR reminder alerts, primary care physicians' documentation rate rose to 45% (9% increase; P < 0.01), but it was below the 15% target increase. Better documentation of pediatric height and weight by family physicians is needed to improve monitoring of children's growth trajectories. Additional strategies to increase documentation rates are needed.

Early determinants of metabolically healthy obesity in young adults: study of the Northern Finland Birth Cohort 1966

BACKGROUND

A body of literature suggests a metabolically healthy phenotype in individuals with obesity. Despite important clinical implications, the early origins of metabolically healthy obesity (MHO) have received little attention.

OBJECTIVE

To assess the prevalence of MHO among the Northern Finland Birth Cohort 1966 (NFBC1966) at 31 years of age, examine its determinants in early life taking into account the sex specificity.

METHODS

We studied 3205 term-born cohort participants with data available for cardio-metabolic health outcomes at 31 years, and longitudinal height and weight data. After stratifying the population by sex, adult BMI and a strict definition of metabolic health (i.e., no risk factors meaning metabolic health), we obtained six groups. Repeated childhood height and weight measures were used to model early growth and early adiposity phenotypes. We employed marginal means adjusted for mother and child covariates including socio-economic status, birth weight and gestational-age, to compare differences between the groups.

RESULTS

The prevalence of adult MHO was 6% in men and 13.5% in women. Differences in adult metabolic status were linked to alterations in BMI and age at adiposity peak in infancy (p < 0.0003 in men and p = 0.027 in women), and BMI and age at adiposity rebound (AR) (p < 0.0001 irrespective of sex). Compared to MHO, metabolically unhealthy obese (MUO) women were five and a half months younger at AR (p = 0.007) with a higher BMI while MUO men were four months older (p = 0.036) with no difference in BMI at AR.

CONCLUSION

At the time of AR, MHO women appeared to be older than their MUO counterparts while MHO men were younger. These original results support potential risk factors at the time of adiposity rebound linked to metabolic health in adulthood. These variations by sex warrant independent replication.

Growth Pattern in Children with Systemic Lupus Erythematosus

OBJECTIVES

Children with childhood-onset systemic lupus erythematosus (cSLE) enter adulthood with considerable morbidity. Of the recognized morbidities, growth failure is unique to cSLE. The aim of this study was to evaluate the growth pattern in children with cSLE longitudinally and identify possible risk factors.

METHODS

Serial anthropometric measurements of cSLE patients were obtained over two years and expressed as z-scores. Parental heights were obtained to calculate target height. Parent-adjusted height z-score was calculated as the difference between height z-score and target height. Growth failure was defined as parent-adjusted height z-score < -1.50. Risk factors that might have contributed to growth failure were evaluated including the presence of growth failure at baseline, disease activity, disease duration, and cumulative steroid doses.

RESULTS

Twenty-five patients were included in the study. Growth failure was observed in eight patients with an overall incidence of 32.0% (95% confidence interval (CI): 14-50%). When comparing the cohort with and without growth failure, the factors that determined growth failure was the pre-existence of growth failure at the time of diagnosis (z-score < -1.95 vs. 0.35; p < 0.001); higher cumulative steroid dose (15.8 vs. 9.1 g ; p = 0.061); and tendency for longer disease duration (5.4 vs. 3.7 years; p = 0.240). However, the severity of disease activity at the time of diagnosis was not a significant contributing factor (12 vs. 14; p = 0.529).

CONCLUSIONS

Children with cSLE are at risk of having a negative effect on height including patients with pre-existing growth failure, high cumulative steroid dose, and longer disease duration. However, longitudinal prospective studies are needed to examine damage over time to improve health-related quality of life.

Determinants of Adiposity Rebound Timing in Children

OBJECTIVE

Adiposity rebound (AR) or BMI (body mass index) rebound refers to the increase in BMI following the minimum BMI in early childhood. Early AR (before age 5) is predictive of adult obesity. To determine how 4 domains - demographics, maternal BMI, food security, and behavioral characteristics - may affect timing of AR.

STUDY DESIGN

A total of 248 children, ages 2.5-3.5 years, in Latino farmworker families in North Carolina were examined at baseline and every 3 months for 2 years. BMI was plotted serially for each child and the onset of BMI rebound was determined by visual inspection of the graphs. Given the ages of the children, all rebounds were detected before age 5 years and were deemed "early," whereas other children were classified as "nonrebounders." Classes were then compared in terms of the 4 domains with the use of bivariate analyses and linear mixed models.

RESULTS

A total of 131 children demonstrated early rebound, 59 children were nonrebounders, and a further 35 had inconclusive data. Parents of early rebounders were less likely to have documentation permitting legal residence in the US. Mothers of early rebounders were on average 3 BMI units heavier. Sex, household food security, diet quality, caloric intake, and daily activity did not differ between classes. In multivariable analysis, female sex, limited maternal education, increased maternal BMI, and increased caloric intake were significant predictors of early rebound.

CONCLUSION

High maternal BMI was the strongest predictor of early BMI rebound, but increased caloric intake also was significant. Limiting excess calories could delay premature AR and lower the risk of future obesity.

Development of Distinct Body Mass Index Trajectories Among Children Before Age 5 Years: A Population-Based Study

The prevalence of childhood obesity has increased over the past 3 decades. This study was designed to understand how childhood body mass index (BMI) influences later risk of obesity. We calculated BMIs for children residing in Olmsted County, Minnesota, between January 1, 2005 and December 31, 2012 using medical records data. We defined homogenous BMI trajectory clusters using a nonparametric hill-climbing algorithm. Overall, 16,538 (47%) children had >3 weight assessments at least 1 year apart and were included in the analyses. Within the 8-year follow-up period, children who were younger than 2 years and overweight had a 3- fold increase of obesity (adjusted hazard ratio [HR] = 3.24; 95% confidence interval [CI] = 2.69-3.89) and those aged 5 years and overweight had a 10-fold increased risk of obesity (adjusted HR = 9.97, 95% CI = 8.55-11.62). Three distinct BMI trajectories could be distinguished prior to 5 years of age. The risk of developing obesity in those who are overweight increased dramatically with increasing age. Interventions to prevent obesity need to occur prior to school age to prevent children from entering unhealthy BMI trajectories.

The rise and the recent decline of childhood obesity in Swedish boys: the BEST cohort

BACKGROUND/OBJECTIVES

Childhood obesity increases the risk for adult obesity and diseases. The aim of this study was to investigate secular changes of childhood body mass index (BMI), overweight and obesity in boys born during 1946-2006, using the population-based BMI Epidemiology STudy (BEST) cohort in Gothenburg, Sweden.

SUBJECTS/METHODS

We collected height and weight from archived school health records for boys born every 5 years 1946-2006 (birth cohort 1946 n=1584, each birth cohort 1951-2006 n=425). Childhood BMI at 8 years of age was obtained for all the participants.

RESULTS

Childhood BMI increased 0.18 kg m^-2 (95% confidence interval: 0.16-0.20) per decade increase in birth year, during 1946-2006. The increase was significant from birth year 1971, peaked 1991 and was then followed by a stabilization or tendency to a reduction. Next, we aimed to thoroughly explore the trend after birth year 1991 and therefore expanded birth cohorts 1991 (n=1566), 2001 (n=6478) and 2006 (n=6515). Importantly, decreases in mean BMI (P<0.01), prevalences of overweight (P<0.01) and obesity (P<0.05) were observed after birth year 1991. For boys born in Sweden and with parents born in Sweden, a substantial reduction in the prevalences of overweight (-28.6%, P<0.001) and obesity (-44.3%, P<0.001) were observed between birth year 1991 and birth year 2006.

CONCLUSIONS

This long-term study captures both the rise and the recent decline of childhood obesity. As childhood obesity is strongly associated with subsequent adult obesity, we anticipate a similar reduction in adult obesity during the coming decades in Swedish men.

Evaluating Latino WIC Mothers' Perceptions of Infant's Healthy Growth: A Formative Assessment

OBJECTIVES

This article reports on a formative assessment with Latino mothers in the Special Supplemental Nutrition Program for Women, Infants, and Children (WIC) evaluating knowledge, attitudes and behaviors regarding healthy growth for infants and their understanding of infant growth monitoring. Further, we explored the acceptability and feasibility of mothers' monitoring their infants' growth. This assessment includes healthy growth perceptions from mothers, caregivers and from WIC staff.

METHODS

Utilizing a mixed method approach, this assessment included qualitative focus groups with WIC mothers that included a growth chart plotting exercise and a quantitative survey. In-depth interviews with clinic staff discussing protocols used in assessing children's growth were also conducted in one WIC clinic.

RESULTS

Focus group participants included 34 mothers and 19 caregivers with a mean age of 32 years; 90 % identified as Latino. Themes included concern for underweight status, and reports of limited conversations between mothers and healthcare providers regarding overweight status, and infant feeding practices/beliefs that may contribute to feeding behaviors associated with risk for excess weight gain during infancy. Growth charts were well received, mothers were able to plot with modest accuracy; but effectiveness of growth plotting might be limited without refinement for health literacy and the provision of culturally-sensitive education in relation to feeding behaviors to support healthy infant growth.

CONCLUSIONS

This represents a first effort in evaluating Latino mothers' perceptions of infants' healthy growth and use growth charts as a potential tool that can help prevent excess weight gain in early infancy.

How has child growth around adiposity rebound altered in Scotland since 1990 and what are the risk factors for weight gain using the Growing Up in Scotland birth cohort 1?

BACKGROUND

Adiposity rebound is considered critical to the development of overweight and obesity. The purpose of this study was to investigate how growth has changed in comparison to the UK 1990 BMI growth reference curves between the ages 4-8 years and identify any marked deviations in growth. We also examined potential maternal and child risk/protective factors associated with the altered growth patterns.

METHODS

We used data from birth cohort 1 of the Growing Up in Scotland study. Height and weight data (N = 2 857) were available when the children were aged approximately 4 (sweep 4), 6 (sweep 6) and 8 years (sweep 7). For each child, percentile change per month was calculated to identify deviations from the UK 1990 growth patterns. Marked changes (>10 % annual change) in percentiles or weight category between each sweep for each child were considered as reflecting a decreasing (leptogenic), increasing (obesogenic) or no change pattern. Logistic regression was used to explore which maternal or child risk factors were associated with belonging to the different growth patterns.

RESULTS

Sixty six percent (66 %) of the cohort did not show marked changes in BMI percentile and growth compared to the UK 1990 reference population. However, the median BMI percentile of this group was around the 70th. The most common deviation in BMI percentile was early decrease (11.5 %). In terms of weight categories, contemporary maternal obesity (odd ratio (OR) =2.89; 95 % confidence interval (CI) 2.09, 3.98) and mother smoking during pregnancy (OR =1.56; 95 % CI 1.13, 2.15) were found to be significantly associated with increased odds of obesogenic growth trajectory relative to no change trajectory. Breastfeeding (OR = 1.18; 95 % CI 0.88, 1.57) was also associated with increased odds of obesogenic growth but this was not significant in the adjusted model.

CONCLUSIONS

This study has shown that there is a substantial shift in the general population distribution of BMI since 1990. We identified maternal weight status as the strongest obesogenic factor and this is an indication that more innovative obesity preventive strategies should also consider intergenerational approaches.

Nutrient Intakes in Early Life and Risk of Obesity

There is increasing evidence that environmental factors in early life predict later health. The early adiposity rebound recorded in most obese subjects suggests that factors promoting body fat development have operated in the first years of life. Birth weight, growth velocity and body mass index (BMI) trajectories seem to be highly sensitive to the environmental conditions present during pregnancy and in early life (“The first 1000 days”). Particularly, nutritional exposure can have a long-term effect on health in adulthood. The high protein-low fat diet often recorded in young children may have contributed to the rapid rise of childhood obesity prevalence during the last decades. Metabolic programming by early nutrition could explain the development of later obesity and adult diseases.

Assessing long-term QALYs gain from averting and reversing overweight and obesity in childhood

BACKGROUND

Interventions to tackle childhood obesity have been devised in response to the rising prevalence of childhood obesity. However, efficiency of these interventions remains a concern. Cost-utility analysis, representing health benefits in terms of quality-adjusted life years (QALYs), is a type of economic evaluation that has widely been recommended in assessing efficiency of health interventions. However, certain limitations in using QALYs remain specifically difficult in QALYs estimation. This study estimates the long-term QALYs gain from reversing childhood obesity in Thailand.

METHODS

An economic model was developed to estimate long-term QALYs of the youth aged 3-18 for the BMI status in childhood, which were categorized into three groups: normal weight, overweight, and obese. Long-term QALYs were estimated between ages 35 and 100, according to children's age, sex, and BMI status. Differences in QALYs between BMI status groups were calculated to represent the QALYs gain for youth from reversing obesity and overweight. The future outcomes were discounted at 3 % per annum in the base-case analysis; the discount rates of 0, 1.5, 3.5, and 5 % were also applied in the sensitivity analyses.

RESULTS

QALYs gained from reversing childhood obesity increase with age, starting from 0.040 and 0.083 QALYs at age 3 to 0.590 and 0.553 QALYs at age 18 in boys and girls, respectively. Reversing overweight and obesity in girls produces more QALYs than in boys between ages 3 and 17.

CONCLUSIONS

Efficiency is an important issue in allocating public healthcare resources to maximize social benefits. The results of this study facilitate long-term QALYs estimation with respect to BMI status in childhood, which could encourage more routine economic evaluation of child obesity interventions and maximize their health benefits.

Secular Changes of Adiposity and Motor Development in Czech Preschool Children: Lifestyle Changes in Fifty-Five Year Retrospective Study

Secular trends of adiposity and motor development in preschool children since the fifties of the last century up to the beginning of this millennium were analyzed so as to reveal possible changes due to continuously differentiating lifestyle. In preschool children (n = 3678) height, weight, skinfold thickness over triceps, subscapular, and suprailiac were measured by Harpenden caliper in 1957, 1977, 1980, 1985, 1990, and 2012. Simultaneously, motor performance was tested by evaluating the achievements in broad jump and throwing a ball, as a marker of adaptation to changing level of physical activity, free games, and exercise. Along the period of five decades the values of skinfold thickness increased significantly until 2012, mainly on the trunk. Simultaneously, the level of motor performance significantly decreased. Modifications of the way of life during the mentioned five decades characterized by sedentarism and inadequate food intake as related to energy output influenced negatively both adiposity and motor performance already in preschool children. Mostly increased deposition of fat on the trunk which is considered as a marker of possible development of metabolic syndrome was apparent already in preschool age, indicating the importance of early intervention concerning also physical activity and availability for exercise since early life.

The decline in BMI among Japanese women after World War II

The body mass index (BMI) of the Japanese is significantly lower than is found in other high-income countries. Moreover, the average BMI of Japanese women is lower than that of Japanese men, and the age-specific BMI of Japanese women has decreased over time. The average BMI of Japanese women at age 25 decreased from 21.8 in 1948 to 20.4 in 2010 whereas that of men increased from 21.4 to 22.3 over the same period. We examine the long-term BMI trend in Japan by combining several historical data sources spanning eleven decades, from 1901 to 2012, to determine not only when but also how the BMI decline among women began: whether its inception was period-specific or cohort-specific. Our nonparametric regression analysis generated five findings. First, the BMI of Japanese women peaked with the 1930s birth cohort. This means that the trend is cohort-specific. Second, the BMI of men outpaced that of women in the next cohort. Third, the BMI of Japanese children, boys and girls alike, increased steadily throughout the 20th century. Fourth, the gender difference in the BMI trend is due to a gender difference in the weight trend, not the height trend. Fifth, these BMI trends are observed in urban and rural populations alike. We conclude that the BMI decline among Japanese women began with those who were in their late teens shortly after World War II.

How Has the Age-Related Process of Overweight or Obesity Development Changed over Time? Co-ordinated Analyses of Individual Participant Data from Five United Kingdom Birth Cohorts

BACKGROUND

There is a paucity of information on secular trends in the age-related process by which people develop overweight or obesity. Utilizing longitudinal data in the United Kingdom birth cohort studies, we investigated shifts over the past nearly 70 years in the distribution of body mass index (BMI) and development of overweight or obesity across childhood and adulthood.

METHODS AND FINDINGS

The sample comprised 56,632 participants with 273,843 BMI observations in the 1946 Medical Research Council National Survey of Health and Development (NSHD; ages 2-64 years), 1958 National Child Development Study (NCDS; 7-50), 1970 British Cohort Study (BCS; 10-42), 1991 Avon Longitudinal Study of Parents and Children (ALSPAC; 7-18), or 2001 Millennium Cohort Study (MCS; 3-11). Growth references showed a secular trend toward positive skewing of the BMI distribution at younger ages. During childhood, the 50th centiles for all studies lay in the middle of the International Obesity Task Force normal weight range, but during adulthood, the age when a 50th centile first entered the overweight range (i.e., 25-29.9 kg/m2) decreased across NSHD, NCDS, and BCS from 41 to 33 to 30 years in males and 48 to 44 to 41 years in females. Trajectories of overweight or obesity showed that more recently born cohorts developed greater probabilities of overweight or obesity at younger ages. Overweight or obesity became more probable in NCDS than NSHD in early adulthood, but more probable in BCS than NCDS and NSHD in adolescence, for example. By age 10 years, the estimated probabilities of overweight or obesity in cohorts born after the 1980s were 2-3 times greater than those born before the 1980s (e.g., 0.229 [95% CI 0.219-0.240] in MCS males; 0.071 [0.065-0.078] in NSHD males). It was not possible to (1) model separate trajectories for overweight and obesity, because there were few obesity cases at young ages in the earliest-born cohorts, or (2) consider ethnic minority groups. The end date for analyses was August 2014.

CONCLUSIONS

Our results demonstrate how younger generations are likely to accumulate greater exposure to overweight or obesity throughout their lives and, thus, increased risk for chronic health conditions such as coronary heart disease and type 2 diabetes mellitus. In the absence of effective intervention, overweight and obesity will have severe public health consequences in decades to come.

Time trends in BMI, body fatness, and adiposity rebound among boys from Kraków (Poland) from 1983 to 2010

OBJECTIVES

The prevalence of childhood obesity has been increasing during the last decades in many countries, but less is known about secular trends in growth curves covering the whole childhood span. The main purpose of this study was to explore changes in body weight, height, BMI, percent body fat (%BF), adiposity rebound (AR), and pubertal timing in boys from Kraków between 1983 and 2010.

METHODS

Totally, 4,986 boys (3-18 years) were measured during cross-sectional studies. Using the results of height, weight, and skinfold measurements, BMI and %BF were calculated. The LMS method was used to construct BMI and %BF percentiles. Three cut-off points were distinguished in individual age groups of the subjects-below the 15th percentile, 50th percentile, and above the 85th percentile. The mean age at pubarche was calculated by the probit method.

RESULTS

The boys from 2010 were taller and heavier than the boys from 1983. Before the time of AR, boys from 2010 had lower BMI, but after AR had higher BMI than boys from 1983. An earlier AR appeared in all BMI 2010 percentile curves as compared to 1983. The boys from 2010 also showed an acceleration of sexual maturation and earlier Tanner Stage II, equaling 11.80 years.

CONCLUSIONS

In boys from 2010, AR occurs earlier than in boys from 1983. Changes in timing of AR cannot be explained only by changes in degree of body adiposity. Early AR could be a marker of the acceleration of development.

Should age-period-cohort studies return to the methodologies of the 1970s?

Social scientists have recognized the importance of age-period-cohort (APC) models for half a century, but have spent much of this time mired in debates about the feasibility of APC methods. Recently, a new class of APC methods based on modern statistical knowledge has emerged, offering potential solutions. In 2009, Reither, Hauser and Yang used one of these new methods - hierarchical APC (HAPC) modeling - to study how birth cohorts may have contributed to the U.S. obesity epidemic. They found that recent birth cohorts experience higher odds of obesity than their predecessors, but that ubiquitous period-based changes are primarily responsible for the rising prevalence of obesity. Although these findings have been replicated elsewhere, recent commentaries by Bell and Jones call them into question - along with the new class of APC methods. Specifically, Bell and Jones claim that new APC methods do not adequately address model identification and suggest that "solid theory" is often sufficient to remove one of the three temporal dimensions from empirical consideration. They also present a series of simulation models that purportedly show how the HAPC models estimated by Reither et al. (2009) could have produced misleading results. However, these simulation models rest on assumptions that there were no period effects, and associations between period and cohort variables and the outcome were perfectly linear. Those are conditions under which APC models should never be used. Under more tenable assumptions, our own simulations show that HAPC methods perform well, both in recovering the main findings presented by Reither et al. (2009) and the results reported by Bell and Jones. We also respond to critiques about model identification and theoretically-imposed constraints, finding little pragmatic support for such arguments. We conclude by encouraging social scientists to move beyond the debates of the 1970s and toward a deeper appreciation for modern APC methodologies.

Population-level obesity surveillance: monitoring childhood body mass index z-score in a safety-net system

OBJECTIVE

To determine the utility of repeated patient-level body mass index (BMI) measurements among higher-risk patients seen at safety-net clinics as a community-level monitoring tool for overweight and obesity population trends.

METHODS

Data from a network of urban, federally qualified community health centers with computerized tracking of BMI at sequential outpatient visits were analyzed. We performed a longitudinal observational study over 8 years (2005-2012) with children stratified by weight status groups on the basis of BMI. Changes in BMI z-scores were used to estimate population trends among children 2 to 11 years old, with at least 2 visits (at least 1 year apart), for whom weight and height were measured.

RESULTS

Among children (n = 33,542), the rate of overweight was 16% and rate of obesity was 18% at their last visit. Children were followed for an average of 3.24 ± 1.76 years to measure trends and change in weight status from earlier to later childhood. Children who were obese at first visit had increased odds (adjusted odds ratio 27.8, 95% confidence interval 25.6-30.2) of being obese by last visit. Mean change in BMI z-score per person-year of observation was 0.10 ± 0.38, with a differing rate of change based on weight status category at last visit (not overweight = 0.06 ± 0.39; overweight = 0.17 ± 0.34; obese = 0.19 ± 0.36). Change in BMI z-score per person-year decreased for 40% of obese children; however, their weight status group remained unchanged.

CONCLUSIONS

Childhood obesity prevalence was high, with substantial progression to overweight and obesity from first to last visit. Clinically derived BMI z-score per person-year measures can effectively show population trends not observed using standard weight status categories.

What can providers learn from childhood body mass index trajectories: a study of a large, safety-net clinical population

OBJECTIVE

To describe childhood weight gain using body mass index (BMI) z-score trajectories in a low-income urban safety-net population and identify among gender- and race/ethnicity-specific groups any trends for increased risk.

METHODS

A retrospective cohort study was conducted among 2- to 12-year-old patients (2006-2013) visiting a safety-net provider. BMI z-score trajectories were calculated overall, for gender- and race/ethnicity-specific groups, and for peak BMI percentile subgroups to describe weight gain longitudinally.

RESULTS

From 2006 to 2013, a total of 26,234 eligible children were followed for an average of 3.7 years. At baseline (mean age, 4.2 years), 74% of patients were at a normal weight compared to 65% at most recent observation (mean age, 7.8 years). All gender and race/ethnicity subgroups showed increasing average BMI z-scores during childhood. Children consistently under the 50th percentile and those of white race had the most stable BMI z-score trajectories. BMI z-score increased with increasing age in all subgroups. Hispanic boys and black girls had the most significant increase in BMI z-score during this observation period. Children observed in early childhood and whose BMI exceeded the 95th percentile at any time were often already overweight (20%) or obese (36%) by 3 years of age.

CONCLUSIONS

The entire population demonstrated an upward trend in BMI z-score trajectory. This trend was most notable among black girls and Hispanic boys. Many obese children were already overweight by age 3, and persistence of obesity after 3 years of age was high, suggesting that intervention before age 3 may be essential to curbing unhealthy weight trajectories.

Alterations in innate and adaptive immune leukocytes are involved in paediatric obesity

BACKGROUND

Adipose tissue is the main source of the cytokines and adipokines that are increased in the context of obesity. The production of reactive oxygen species (ROS) and cytokines by circulating immune cells can be regulated by these pro-inflammatory factors even before infiltration into adipose tissue.

OBJECTIVE

To investigate the alterations that can occur in circulating monocytes and lymphocytes in paediatric obesity.

METHODS

In this study, 54 paediatric obese patients and 30 age-matched metabolically healthy individuals were enrolled. Intracellular cytokines were analyzed after phorbol myristate acetate (PMA) or leptin plus PMA stimulation of lymphocytes and monocytes by flow cytometry. ROS generation was measured using dichlorofluorescein-diacetate. Both a 'stimulation index' and a 'fold of increase' were calculated for statistical purposes.

RESULTS

Both interferon gamma (IFN-γ) production by circulating CD4+ and CD8+ lymphocytes and ROS production by monocytes following PMA stimulation were increased in obese patients. Leptin induced an increased production of IFN-γ in both subsets of T cells and tumour necrosis factor alpha in monocytes, and linoleic acid induced a higher ROS production in monocytes.

CONCLUSIONS

The distinct functional responses of circulating cells suggest that alterations in both innate and adaptive immune cells are involved in the maintenance of low-grade inflammation in paediatric obesity.

Measurement and Interpretation of Body Mass Index During Childhood and Adolescence

The landscape of childhood health and disease has changed over the past century, and school nurses are now in a unique position to address the conditions that lead to chronic disease, such as obesity. Measuring body mass index (BMI) during childhood and adolescence is the recommended method for screening and/or monitoring obesity in school communities. Yet changes in the size, proportion, and distribution of fat mass and fat-free mass during growth and development introduce challenges to interpreting BMI measurements. Understanding these challenges and ensuring accurate measurement techniques are the foundation for implementing school-based BMI measurement programs. This article will provide an overview of body composition during childhood and adolescence, introduce strategies to improve the accuracy of BMI measurements, and explore the school nurse's role in BMI surveillance and/or screening activities.

Preventing childhood obesity: what are we doing right?

After decades of increases, the prevalence of childhood obesity has declined in the past decade in New York City, as measured in children participating in the Special Supplemental Nutrition Program for Women, Infants, and Children (WIC) and public school students, with the greatest reductions occurring in the youngest children. Possible explanations were changes in demographics; WIC, day care, and school food policies; citywide obesity prevention policies, media messages; and family and community food consumption. Although the decreases cannot be attributed to any one cause, the most plausible explanation is changes in food consumption at home, prompted by media messages and reinforced by school and child care center policy changes. Continued media messages and policy changes are needed to sustain these improvements and extend them to other age groups.

Characterization of the infant BMI peak: sex differences, birth year cohort effects, association with concurrent adiposity, and heritability

OBJECTIVES

To characterize an early trait in the BMI-for-age curve, the infant BMI peak.

METHODS

BMI-for-age curves were produced for 747 non-Hispanic, white Fels Longitudinal Study participants, from which individual age (AgePeak ) and BMI (BMIPeak ) at maximum infant BMI were estimated. Multivariable general linear regression was used to examine the effects of sex and birth year cohort (1929-1950, 1951-1970, and 1971-2010) on AgePeak and BMIPeak , with associations between BMIPeak and concurrent sum of four skinfold thicknesses assessed in a subsample (N = 155). Heritability (h(2) ) of AgePeak and BMIPeak was estimated using maximum-likelihood variance components analysis.

RESULTS

AgePeak occurred at 9 months of age in both sexes, but BMIPeak was 0.4 kg/m(2) higher for boys than for girls (P-value < 0.001). Infants born between 1971 and 2010 experienced a 1.5 month earlier AgePeak and a 0.35 kg/m(2) lower BMIPeak than infants born between 1929 and 1950 (P-values < 0.001). Skinfold thickness explained 37% of the variance in BMIPeak in boys and 20% of the variance in girls (p-values < 0.001). AgePeak and BMIPeak were significantly heritable (h(2) = 0.54 and 0.75, respectively).

CONCLUSIONS

Both AgePeak and BMIPeak decreased over successive birth year cohorts in the Fels Longitudinal Study. Despite a positive association of BMIPeak with concurrent adiposity, AgePeak appears to occur later than does the well-documented peak in infant fat mass and BMIPeak does not capture known sex differences in infant adiposity. Strong heritability of these infant BMI traits suggests investigation of genetic control, and validation of their relationship to body composition is greatly needed.

The positive association of obesity variants with adulthood adiposity strengthens over an 80-year period: a gene-by-birth year interaction

OBJECTIVE

To test the hypothesis that the statistical effect of obesity-related genetic variants on adulthood adiposity traits depends on birth year.

METHODS

The study sample included 907 related, non-Hispanic White participants in the Fels Longitudinal Study, born between 1901 and 1986, and aged 25-64.99 years (474 females; 433 males) at the time of measurement. All had both genotype data from which a genetic risk score (GRS) composed of 32 well-replicated obesity-related common single nucleotide polymorphisms was created, and phenotype data [including body mass index (BMI), waist circumference, and the sum of four subcutaneous skinfolds]. Maximum likelihood-based variance components analysis was used to estimate trait heritabilities, main effects of GRS and birth year, GRS-by-birth year interaction, sex, and age.

RESULTS

Positive GRS-by-birth year interaction effects were found for BMI (p < 0.001), waist circumference (p = 0.007), and skinfold thickness (p < 0.007). For example, each one-allele increase in GRS was estimated to result in a 0.16 increase in BMI among males born in 1930 compared to a 0.47 increase among those born in 1970.

CONCLUSIONS

These novel findings suggest the influence of common obesity susceptibility variants has increased during the obesity epidemic.

Genetic risk for earlier menarche also influences peripubertal body mass index

It is unclear whether earlier age at menarche is associated with higher body mass index (BMI) because they share a common genetic underpinning. We investigated the impact of single nucleotide polymorphisms (SNPs) influencing menarche timing on peripubertal BMI. For 556 Fels Longitudinal Study children (277 boys/279 girls) born 1928-1992, a genetic risk score (GRS(42)) was computed as the sum of the number of risk alleles in 42 putative menarche SNPs. Serial BMI Z-scores within ±6.99 years from each individual's age at peak height velocity (Age@PHV) were grouped into seven time points (-6 years, -4 years, -2 years, Age@PHV, +2 years, +4 years, and +6 years). Heritability of BMI ranged from 0.53 to 0.85 across the time points. The effect of GRS(42) on BMI Z-scores at each time point was modeled using variance components-based procedures. GRS(42) had a significant (P < 0.05) effect at every time point; an increase of one risk allele was associated with an increase of 0.03-0.08 BMI Z-scores. A separate score (GRS(29)) was computed that excluded 13 of the menarche SNPs previously documented to also influence adiposity; significant main effects were observed at Age@PHV+4 and +6 years. This finding supports a causal effect of advanced sexual development on post-Age@PHV BMI. Significant positive GRS(42) (or GRS(29))-by-birth year interactions indicate that some genetic influences on BMI have amplified over the 20th century. This gene-by-environment interaction also suggests that children with a genetic predisposition to earlier sexual development might avoid elevated BMI through alteration of their nutritional environment.

Emergence and persistence of overweight and obesity in 7- to 11-year-old children

AIM

After dramatic rises in paediatric obesity, the critical period for obesity onset may now be pre-adolescence.

METHODS

We monitored adiposity over 4 years in 400 children aged 7-9 years recruited from schools in London. Weight, height, waist circumference (WC) and fat mass were measured annually. Weight status was defined using International Obesity Task Force (IOTF) criteria, and standardised scores and percentiles used British 1990 reference data.

RESULTS

BMI, WC and fat mass index all tracked strongly over time (average correlation for BMI = 0.95). Emergence of obesity was relatively uncommon: only 2% of the total sample increased from overweight to obese over the 4-year period, and this was nearly matched by the 1.3% that reduced from obese to overweight. However, more children (6%) moved from healthy weight to overweight than the reverse direction (2%). There were greater absolute gains in adiposity in children with higher baseline weight status, but this was disguised in analyses using standardised scores. Obesity was not an emergent trait in middle childhood, but rates were already high and, in absolute terms, adiposity increased more in overweight and obese than healthy weight children.

CONCLUSION

These results highlight the need for active management of obesity in middle childhood.

The genetics of obesity in transition

Recent advances in human genetics have revealed a number of genes influencing the susceptibility to obesity and related conditions, but it is likely that their contribution to disease is contingent on numerous environmental factors. As the obesity epidemic has occurred over a relatively short period of recent history, use of gene-by-year of birth analysis may be a useful approach for quantifying, in aggregate, the interaction between genetic susceptibility to obesity and the numerous known and unknown environmental factors that have changed during nutrition and health transitions globally during this recent increase in obesity rates. Evidence from one family-based longitudinal study set in the United States is showcased, which points to significant increases in the effect of common genetic variants on childhood and adulthood BMI over an 80 year period spanning from 1929 to the present. First, common genetic variants previously known to be associated with age at menarche through genome-wide association analysis were examined in aggregate using a genetic risk score approach. The menarche genetic risk score, composed of 42 single-nucleotide polymorphisms (SNPs) was significantly associated with peri-pubertal BMI in both boys and girls, but the magnitude of the association was strongly dependent on year of birth, with greater effect as birth year increased. Second, a similar approach was taken using instead a BMI genetic risk score composed of 32 common variants previously found to be associated with BMI. This score was strongly associated with adulthood BMI, waist circumference, and skinfold thickness, as expected, but the magnitude of the association increased with later year of birth. Such gene-environment interactions call for greater focus on the mechanisms by which environmental factors impact the functional output of the human genome, including how epigenetic mechanisms may be altered during social, technological, nutritional, and ecological transitions.

Secular trends in the fat and fat-free components of body mass index in children aged 8-18 years born 1958-1995

BACKGROUND

It is unknown whether the secular trend in childhood BMI reflects increases in fat-free mass as well as fat mass.

METHODS

This study decomposed BMI trends in 488 participants in the Fels Longitudinal Study born between 1958-1995 and aged 8-17.99 years into their fat and fat-free components. Generalized estimating equations estimated birth year cohort (1958-1970, 1971-1983, 1984-1995) effects on 2208 observations of BMI, fat mass index (FMI = fat mass (kg)/height (m)(2)) and fat-free mass index (FFMI = fat-free mass (kg)/height (m)(2)).

RESULTS

BMI in boys increased across cohorts, with those born between 1984-1995 being 2 kg/m(2) larger than those born between 1958-1970 (p = 0.001) and increases in FMI were highly significant (p-values < 0.001). FFMI did not differ by cohort. In girls, there was a significant advantage in BMI (1.2 kg/m(2)) and FFMI (0.8 kg/m(2)) of the 1984-1995 cohort compared to the 1971-1983 cohort (p-values < 0.05).

CONCLUSIONS

Because the long term trend in childhood BMI in boys appears to be driven by an increase in total body adiposity, evidence is provided to support current knowledge on the predicted deleterious long-term consequences of the childhood obesity epidemic in boys. Research is needed to confirm whether recent changes in BMI in girls are due to increases in fat-free mass resulting from changes in behaviour and lifestyle not yet manifest in boys.