BackgroundPhysical activity (PA), weight-bearing exercises (WBE) and muscle strength contribute to skeletal development, while sedentary behaviour (SB) adversely affects bone health. Previous studies examined the isolated effect of PA, SB or muscle strength on bone health, which was usually assessed by x-ray methods, in children. Little is known about the combined effects of these factors on bone stiffness (SI) assessed by quantitative ultrasound. We investigated the joint association of PA, SB and muscle strength on SI in children.MethodsIn 1512 preschool (2- < 6 years) and 2953 school children (6–10 years), data on calcaneal SI as well as on accelerometer-based sedentary time (SED), light (LPA), moderate (MPA) and vigorous PA (VPA) were available. Parents reported sports (WBE versus no WBE), leisure time PA and screen time of their children. Jumping distance and handgrip strength served as indicators for muscle strength. The association of PA, SB and muscle strength with SI was estimated by multivariate linear regression, stratified by age group. Models were adjusted for age, sex, country, fat-free mass, daylight duration, consumption of dairy products and PA, or respectively SB.ResultsMean SI was similar in preschool (79.5 ± 15.0) and school children (81.3 ± 12.1). In both age groups, an additional 10 min/day in MPA or VPA increased the SI on average by 1 or 2 %, respectively (p ≤ .05). The negative association of SED with SI decreased after controlling for MVPA. LPA was not associated with SI. Furthermore, participation in WBE led to a 3 and 2 % higher SI in preschool (p = 0.003) and school children (p < .001), respectively. Although muscle strength significantly contributed to SI, it did not affect the associations of PA with SI. In contrast to objectively assessed PA, reported leisure time PA and screen time showed no remarkable association with SI.ConclusionThis study suggests that already an additional 10 min/day of MPA or VPA or the participation in WBE may result in a relevant increase in SI in children, taking muscle strength and SB into account. Our results support the importance of assessing accelerometer-based PA in large-scale studies. This may be important when deriving dose–response relationships between PA and bone health in children.

Little is known about the extent that different domains contribute to total sedentary (SED), light (LPA) and moderate-to-vigorous physical activity (MVPA). We aimed to identify domain-specific physical activity (PA) patterns in school-aged children who were assessed by questionnaire and accelerometry. For the study, 298 German school children and adolescents aged 6–17 years wore an accelerometer for one week and completed a PA recall-questionnaire for the same period. Spearman coefficients (r) were used to evaluate the agreement between self-reported and objectively measured PA in five domains (transport, school hours, physical education, leisure-time, organized sports activities). School hours mainly contributed to the total objectively measured SED, LPA and MVPA (55%, 53% and 46%, respectively), whilst sports activities contributed only 24% to total MVPA. Compared to accelerometry, the proportion of self-reported LPA and MVPA during school hours was substantially underestimated but overestimated during leisure-time. The agreement of self-reported and objectively measured PA was low for total LPA (r = 0.09, 95% CI (confidence interval): −0.03–0.20) and total MVPA (r = 0.21, 95% CI: 0.10–0.32), while moderate agreement was only found for total SED (r = 0.44, 95% CI: 0.34–0.53), LPA during transport (r = 0.59; 95% CI: 0.49–0.67) and MVPA during organized sports activities (r = 0.54; 95% CI: 0.38–0.67). Since school hours mainly contribute to total SED, LPA and MVPA and self-reported LPA and MVPA during school were importantly underestimated compared to objectively measured LPA and MVPA, the application of objective measurements is compulsory to characterize the entire activity pattern of school-aged children.

Childhood stress was positively related to both overall and central adiposity measures with lifestyle factors acting as moderators but not as mediators. Thus, lifestyle could be a vulnerability factor in stress-induced adiposity, creating a perspective for multi-factorial obesity prevention, targeting stress and lifestyle factors in parallel.

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Neuromedin U, encoded by the NMU gene, is a hypothalamic neuropeptide that regulates both energy metabolism and bone mass. The beta-2 adrenergic receptor, encoded by the ADRB2 gene, mediates several effects of catecholamine hormones and neurotransmitters in bone. We investigated whether NMU single nucleotide polymorphisms (SNPs) and haplotypes, as well as functional ADRB2 SNPs, are associated with bone stiffness in children from the IDEFICS cohort, also evaluating whether NMU and ADRB2 interact to affect this trait. A sample of 2,274 subjects (52.5% boys, age 6.2±1.8 years) from eight European countries, having data on calcaneus bone stiffness index (SI, mean of both feet) and genotyping (NMU gene: rs6827359, rs12500837, rs9999653; ADRB2 gene: rs1042713, rs1042714), was studied. After false discovery rate adjustment, SI was significantly associated with all NMU SNPs. rs6827359 CC homozygotes showed the strongest association (recessive model, Δ = −1.8, p = 0.006). Among the five retrieved haplotypes with frequencies higher than 1% (range 2.0–43.9%), the CCT haplotype (frequency = 39.7%) was associated with lower SI values (dominant model, Δ = −1.0, p = 0.04) as compared to the most prevalent haplotype. A non-significant decrease in SI was observed in in ADRB2 rs1042713 GG homozygotes, while subjects carrying SI-lowering genotypes at both SNPs (frequency = 8.4%) showed much lower SI than non-carriers (Δ = −3.9, p<0.0001; p for interaction = 0.025). The association was more evident in preschool girls, in whom SI showed a curvilinear trend across ages. In subgroup analyses, rs9999653 CC NMU or both GG ADRB2 genotypes were associated with either lower serum calcium or β-CrossLaps levels (p = 0.01). This study in European children shows, for the first time in humans, a role for NMU gene through interaction with ADRB2 gene in bone strength regulation, more evident in preschool girls.

Objective: To investigate the repeatability of maternal self-reported prenatal, perinatal and early postnatal factors within the IDEFICS (Identification and prevention of dietary-and lifestyle-induced health effects in children and infants) study. Design: Data are from the baseline survey of the longitudinal cohort study IDEFICS in eight European countries. Subjects: A total of 420 parents from eight countries (43-61 per country) were asked to complete the parental questionnaire (PQ) twice at least 1 month apart. Measurements: The PQ assesses prenatal (maternal weight gain), perinatal (child's birth weight and length, Caesarean (C)-section, week of delivery) and early postnatal factors (exclusive breastfeeding, breastfeeding, introduction of solid food). Intraclass correlation coefficients (ICCs) were calculated to compare maternal reports on prenatal, perinatal and early postnatal factors between the first and second PQ. Results: In total, 249 data sets were considered for the analyses. Overall, maternal reports for prenatal and perinatal factors showed higher repeatability (ICC ¼ 0.81-1.00, Pp0.05 for all) than those for early infant nutrition (ICC ¼ 0.33-0.88, Pp0.05 for all). Perfect agreement was found for parental reports on C-section (ICC all ¼ 1.00, Pp0.05). There was stronger agreement for duration of breastfeeding (ICC ¼ 0.71, Pp0.05) compared with exclusive breastfeeding (ICC ¼ 0.33, Pp0.05). Maternal reports showed moderate correlation for the introduction of several types of food (cereals ICC ¼ 0.64, Pp0.05; fruits ICC ¼ 0.70, Pp0.05; meat ICC ¼ 0.83, Pp0.05; vegetables ICC ¼ 0.75, Pp0.05), and high correlation (ICC ¼ 0.88, Pp0.05) for cow's milk. Conclusion: Maternal reports on pregnancy and birth were highly reproducible, but parental recall of early infant nutrition was weaker and should be interpreted more cautiously. 4 There is evidence that birth weight below and above average is associated with overweight and obesity in childhood. 5 Breastfeeding and early infant nutrition are also shown to be influencing factors on children's body weight. 6,7 In most epidemiological studies, these obesity-related factors are usually assessed by parental reports, particularly by maternal reports. Therefore, it is important to assess the quality of parental or rather maternal information within the framework of studies on childhood obesity. Previous studies have investigated the reliability of maternal reports on prenatal, perinatal and on postnatal factors, and suggest that maternal recall data are reproducible for perinatal factors, for example, birth weight, gestational age or medical procedures. 8,9 In contrast, maternal reports on prenatal factors, for example, maternal weight gain during pregnancy, 10 and early infant nutrition, for example, breastfeeding or introduction of solid food, 11,12 showed only moderate agreement or inconsistency in their reliability.Several studies indicated that other factors, for example, time span or the age of the child, have an impact on the repeatability of maternal self...

,9 on behalf of the IDEFICS consortium BACKGROUND/OBJECTIVE: Quantitative ultrasound measurements and bone metabolic markers can help to monitor bone health and to detect impaired skeletal development. Population-based reference values for children may serve as a basis for preventive measures to reduce the risk of osteoporosis and osteoporotic fractures in later life. This is the first paper providing age-, sex-and height-specific reference values for bone stiffness index (SI) and serum carboxy-terminal cross-linking telopeptide of type I collagen (CTX) in healthy, apparently prepubertal children. SUBJECTS/METHODS: In the population-based IDEFICS baseline survey (2007)(2008) and follow-up (2009-2010), 18 745 children from eight European countries were newly recruited. A total of 10 791 2-10.9-year-old and 1646 3-8.9-year-old healthy children provided data on SI of the right and left calcaneus and serum CTX, respectively. Furthermore, height and weight were measured. Percentile curves were calculated using the General Additive Model for Location Scale and Shape (GAMLSS) to model the distribution of SI and CTX depending on multiple covariates while accounting for dispersion, skewness, and the kurtosis of this distribution. RESULTS: SI was negatively associated with age and height in children aged 2-5 years, whereas a positive association was observed in children aged 6-10 years. The dip in SI occurred at older age for higher SI percentiles and was observed earlier in taller children than in smaller children. The CTX reference curves showed a linear-positive association with age and height. No major sex differences were observed for the SI and CTX reference values. CONCLUSION: These reference data lay the ground to evaluate bone growth and metabolism in prepubertal children in epidemiological and clinical settings. They may also inform clinical practice to monitor skeletal development and to assess adverse drug reactions during medical treatments.