Impact of physical activity, sedentary behaviour and muscle strength on bone stiffness in 2-10-year-old children-cross-sectional results from the IDEFICS study.

BACKGROUND: Physical 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. METHODS: In 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. RESULTS: Mean 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. CONCLUSION: This 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.

The association between childhood stress and body composition, and the role of stress-related lifestyle factors--cross-sectional findings from the baseline ChiBSD survey.

BACKGROUND: Stress has been hypothesised to be involved in obesity development, also in children. More research is needed into the role of lifestyle factors in this association. PURPOSE: This study investigates the cross-sectional relationship between stress and body composition and, more importantly, the possible moderating or mediating role of lifestyle factors. METHODS: A total of 355 Belgian children (5-10 years old) participating in the baseline 'Children's Body composition and Stress' survey were included in this study. The following variables were studied: psychosocial stress (i.e. stressful events, emotions and behavioural/emotional problems, salivary cortisol), stress-related lifestyle factors (high-caloric snack consumption frequency, screen exposure time and sleep duration) and body composition parameters [BMI z-score, waist to height ratio (WHtR)]. Using linear regression analyses (adjusted for sex, age and socio-economic status), the relation between stress and body composition and, more importantly, the possible moderating or mediating role of lifestyle factors was tested. RESULTS: No association was observed between body composition and negative emotions, conduct and emotional problems and salivary cortisol. However, negative life events were positively and happiness was negatively associated with BMI z-score and WHtR. Peer problems and WHtR were positively associated in girls only. These associations were not significantly reduced after correction for lifestyle factors. Nevertheless, all lifestyle parameters moderated one or more stress-body composition associations, resulting in even more significant relations after subgroup analysis. CONCLUSION: 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.

Influence of birth weight on calcaneal bone stiffness in Belgian preadolescent children.

The aim of this study was to investigate the relation between birth weight and calcaneal bone stiffness in a large sample of Belgian, healthy, preadolescent children. Participants were 827 children (3.6-11.2 years, 51.6 % boys) from the Belgian cohort of the IDEFICS study. Birth weight was obtained using a parental questionnaire, and quantitative ultrasound (QUS) measurements were performed to determine calcaneal broadband ultrasound attenuation (BUA), speed of sound (SOS), and stiffness index (SI) using the Lunar Achilles device. Average birth weights were 3435.7 ± 512.0 g for boys and 3256.9 ± 471.1 g for girls. Average calcaneal QUS measurements were 89.6 ± 24.0 (23.3-153.9) dB/MHz for BUA, 1621.4 ± 49.6 (1516.3-1776.5) m/s for SOS, and 92.8 ± 15.6 (49.0-163.0) for SI. Birth weight was positively associated with BUA (r = 0.13, p = 0.002) and SOS (r = -0.16, p < 0.001). The associations remained after correcting for age and sex in multiple regression analyses but disappeared after correcting for anthropometric covariates. Our findings suggest that birth weight, as a rough proxy indicator for genetic and environmental influences during intrauterine life, is associated with BUA and SOS in preadolescent children and may therefore influence the risk of osteoporosis later in life. Further studies using QUS are needed to investigate the consistency of the results of this study.

Relationship between markers of body fat and calcaneal bone stiffness differs between preschool and primary school children: results from the IDEFICS baseline survey.

The aim of this study was to investigate the relationship between markers of body fat and bone status assessed as calcaneal bone stiffness in a large sample of European healthy pre- and primary school children. Participants were 7,447 children from the IDEFICS study (spread over eight different European countries), age 6.1 ± 1.8 years (range 2.1-9.9), 50.5 % boys. Anthropometric measurements (weight, height, bioelectrical impedance, waist and hip circumference, and tricipital and subscapular skinfold thickness) as well as quantitative ultrasonographic measurements to determine calcaneal stiffness index (SI) were performed. Partial correlation analysis, linear regression analysis, and ANCOVA were stratified by sex and age group: preschool boys (n = 1,699) and girls (n = 1,599) and primary school boys (n = 2,062) and girls (n = 2,087). In the overall study population, the average calcaneal SI was equal to 80.2 ± 14.0, ranging 42.4-153. The results showed that preschool children with higher body fat had lower calcaneal SI (significant correlation coefficients between -0.05 and -0.20), while primary school children with higher body fat had higher calcaneal SI (significant correlation coefficients between 0.05 and 0.13). After adjusting for fat-free mass, both preschool and primary school children showed an inverse relationship between body fat and calcaneal stiffness. To conclude, body fat is negatively associated with calcaneal bone stiffness in children after adjustment for fat-free mass. Fat-free mass may confound the association in primary school children but not in preschool children. Muscle mass may therefore be an important determinant of bone stiffness.

Domain-Specific Self-Reported and Objectively Measured Physical Activity 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.

Urinary Mineral Concentrations in European Pre-Adolescent Children and Their Association with Calcaneal Bone Quantitative Ultrasound Measurements.

This study investigates differences and associations between urinary mineral concentrations and calcaneal bone measures assessed by quantitative ultrasonography (QUS) in 4322 children (3.1-11.9 years, 50.6% boys) from seven European countries. Urinary mineral concentrations and calcaneal QUS parameters differed significantly across countries. Clustering revealed a lower stiffness index (SI) in children with low and medium urinary mineral concentrations, and a higher SI in children with high urinary mineral concentrations. Urinary sodium (uNa) was positively correlated with urinary calcium (uCa), and was positively associated with broadband ultrasound attenuation and SI after adjustment for age, sex and fat-free mass. Urinary potassium (uK) was negatively correlated with uCa but positively associated with speed of sound after adjustment. No association was found between uCa and QUS parameters after adjustment, but when additionally adjusting for uNa, uCa was negatively associated with SI. Our findings suggest that urinary mineral concentrations are associated with calcaneal QUS parameters and may therefore implicate bone properties. These findings should be confirmed in longitudinal studies that include the food intake and repeated measurement of urinary mineral concentrations to better estimate usual intake and minimize bias.

Different osteocalcin forms, markers of metabolic syndrome and anthropometric measures in children within the IDEFICS cohort.

OBJECTIVE: Osteocalcin (OC), an aboundant non-collagenous bone protein, is inversely associated with parameters of glucose metabolism. Interactions between bone tissue and energy metabolism have not been thoroughly investigated during childhood. This study investigated OC, metabolic parameters and anthropometric characteristics in normal weight and overweight/obese children. METHODS: This study comprised 108 (46 normal weight/62 overweight/obese) Swedish 2-9year old children. Anthropometric data, insulin, glucose, glycosylated haemoglobin (HbA1c), HOMA index, vitamin D, adiponectin, total OC, carboxylated OC (cOC) and undercarboxylated OC (ucOC) were analysed. RESULTS: No difference was found for total OC between the normal and overweight/obese groups, with a mean (±SD) value of 82.6 (±2.8) ng/mL and 77.0 (±2.4) ng/mL, (P=0.11), respectively. Overweight children had lower cOC levels, mean 69.1 (±2.2) ng/mL, vs. normal weight children, mean 75.6 (±2.5) ng/mL (P=0.03). The mean ucOC levels of 7.9 (±0.4) ng/mL in overweight children did not differ vs. normal weight children, mean level 7.0 (±0.4) ng/mL, (P=0.067). None of the three OC forms correlated with any of the measured parameters. CONCLUSIONS: The cOC levels were lower in overweight children. There was no correlation between the three OC forms and any of the measured anthropometric or metabolic parameters. OC has been suggested to have a possible metabolic role, but in general the current study in prepubertal children does not support the hypothesis of an association between OC and a positive metabolic profile.

Association between bone stiffness and nutritional biomarkers combined with weight-bearing exercise, physical activity, and sedentary time in preadolescent children. A case-control study.

Physical activity (PA) and micronutrients such as calcium (Ca), vitamin D (25OHD), and phosphate (PO) are important determinants of skeletal development. This case-control study examined the association of these nutritional biomarkers and different PA behaviours, such as habitual PA, weight-bearing exercise (WBE) and sedentary time (SED) with bone stiffness (SI) in 1819 2-9-year-old children from the IDEFICS study (2007-2008). SI was measured on the calcaneus using quantitative ultrasound. Serum and urine Ca and PO and serum 25OHD were determined. Children's sports activities were reported by parents using a standardised questionnaire. A subsample of 1089 children had accelerometer-based PA data (counts per minute, cpm). Moderate-to-vigorous PA (MVPA) and SED were estimated. Children with poor SI (below the 15th age-/sex-/height-specific percentile) were defined as cases (N=603). Randomly selected controls (N=1216) were matched by age, sex, and country. Odds ratios (OR) for poor SI were calculated by conditional logistic regression for all biomarkers and PA behaviour variables separately and combined (expressed as tertiles and dichotomised variables, respectively). ORs were adjusted for fat-free mass, dairy product consumption, and daylight duration. We observed increased ORs for no sports (OR=1.39, p<0.05), PA levels below 524 cpm (OR=1.85, p<0.05) and MVPA below 4.2% a day (OR=1.69, p<0.05) compared to WBE, high PA levels (<688 cpm) and high MVPA (6.7%), respectively. SED was not associated with SI. ORs were moderately elevated for low serum Ca and 25OHD. However, biomarkers were not statistically significantly associated with SI and did not modify the association between PA behaviours and SI. Although nutritional biomarkers appear to play a minor role compared to the osteogenic effect of PA and WBE, it is noteworthy that the highest risk for poor SI was observed for no sports or low MVPA combined with lower serum Ca (<2.5 mmol/l) or lower 25OHD (<43.0 nmol/l).

Understanding the links among neuromedin U gene, beta2-adrenoceptor gene and bone health: an observational study in European children.

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 ß-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.