Tracking of Environmental Determinants of Bone Structure and Strength Development in Healthy Boys: An Eight-Year Follow Up Study on the Positive Interaction Between Physical Activity and Protein Intake From Prepuberty to Mid-Late Adolescence

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Abstract

High protein (> median:Hprot) vs. moderate (< median:MProt) intake was shown to enhance the positive impact of high physical activity (HPA) on proximal femur BMC/aBMD/Area in healthy prepubertal boys. We tested the hypothesis that this synergistic effect would track and influence bone structure and strength until mid-adolescence. BMC/aBMD/Area was measured at femoral neck (FN) and total hip (TotHip) by DXA in 176 boys at 7.4 ± 0.4 and 15.2 ± 0.5 years (± SD). Distal tibia (DistTib) microstructure and strength were also assessed at 15.2 years by high-resolution peripheral computerized tomography (HR-pQCT) and micro-finite element analysis (µFEA). The positive impact of HProt vs. MProt on FN and TotHip BMC/aBMD/Area, recorded at 7.4 years remained unabated at 15.2 years. At this age, at DistTib, HProt-HPA vs. MProt-HPA was associated (p < 0.001) with larger cross-sectional area (CSA, mm(2) ), trabecular number (Tb.N, mm(-1) ) and lower trabecular separation (Tb.Sp, µm). The interaction between physical activity and protein intake was significant for CSA (p = 0.012) and Tb.N (p = 0.043). Under MProt (38.0 ± 6.9 g.d(-1)), a difference in PA from 168 ± 40 to 303 ± 54 kcal.d(-1) was associated with greater stiffness (kN/mm) and failure load (N) of +0.16 and +0.14 Z-score, respectively. In contrast, under HProt (56.2 ± 9.5 g.d(-1) ), a difference in PA of similar magnitude, from 167 ± 33 to 324 ± 80 kcal.d(-1) , was associated with a larger difference in stiffness and failure load of +0.50 and +0.57 Z-score, respectively. In conclusion, the positive influence of relatively HProt on the impact of HPA on proximal femur macrostructure tracks from prepuberty to mid-late puberty. At this stage, the impact of HProt on HPA is also associated with microstructural changes that should confer greater mechanical resistance to weight-bearing bones. These results underscore the importance of protein intake and exercise synergistic interaction in the early prevention of adult osteoporosis.

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Tracking of Physical Activity from Childhood to Adulthood: A Review

Risto Telama (2009)

The aim of the article was to review studies on the tracking of physical activity in all phases of life from childhood to late adulthood. The majority of the studies have been published since 2000. The follow-up time in most studies was short, the median being 9 years. In men, the stability of physical activity was significant but low or moderate during all life phases and also in longterm follow-ups. In women, the tracking was lower and in many cases non-significant. Among both sexes, stability seems to be lower in early childhood than in adolescence or in adulthood and lower in transitional phases, such as from childhood to adolescence or from adolescence to adulthood, than in adulthood. However, the differences in the stability of physical activity between age groups and between different phases of life were small. The number of tracking studies utilising objective methods to measure physical activity was so small that systematic differences in stability between self-report and objective methods could not be determined. A factor which caused differences in tracking results was the adjustment of correlations for measurement error and other error variance. Adjusted coefficients were clearly higher than unadjusted ones. However, adjustment was done only in very few studies. If the different methods used for estimating habitual physical activity and the failure to control for important covariates in studies of tracking are taken into account, physical activity appears to track reasonably well also in the longer term, for example from adolescence to adulthood. The results of the tracking studies support the idea that the enhancement of physical activity in children and adolescents is of great importance for the promotion of public health.

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In vivo assessment of trabecular bone microarchitecture by high-resolution peripheral quantitative computed tomography.

Stéphanie Boutroy, Mary Bouxsein, Francoise Munoz … (2005)

Assessment of trabecular microarchitecture may enhance the prediction of fracture risk and improve monitoring of treatment response. A new high-resolution peripheral quantitative computed tomography (HR-pQCT) system permits in vivo assessment of trabecular architecture and volumetric bone mineral density (BMD) at the distal radius and tibia with a voxel size of 82 microm3. We determined the short-term reproducibility of this device by measuring 15 healthy volunteers three times each. We compared HR-pQCT measurements in 108 healthy premenopausal, 113 postmenopausal osteopenic, and 35 postmenopausal osteoporotic women. Furthermore, we compared values in postmenopausal osteopenic women with (n = 35) and without previous fracture history (n = 78). We conducted a cross-sectional study in a private clinical research center. We took HR-pQCT measurements of the radius and tibia. Femoral neck and spine BMD were measured in postmenopausal women by dual-energy x-ray absorptiometry. Precision of HR-pQCT measurements was 0.7-1.5% for total, trabecular, and cortical densities and 2.5-4.4% for trabecular architecture. Postmenopausal women had lower density, trabecular number, and cortical thickness than premenopausal women (P < 0.001) at both radius and tibia. Osteoporotic women had lower density, cortical thickness, and increased trabecular separation than osteopenic women (P < 0.01) at both sites. Furthermore, although spine and hip BMD were similar, fractured osteopenic women had lower trabecular density and more heterogeneous trabecular distribution (P < 0.02) at the radius compared with unfractured osteopenic women. HR-pQCT appears promising to assess bone density and microarchitecture at peripheral sites in terms of reproducibility and ability to detect age- and disease-related changes.

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Biomechanical and molecular regulation of bone remodeling.

Alexander Robling, Alesha Castillo, Charles Turner (2006)

Bone is a dynamic tissue that is constantly renewed. The cell populations that participate in this process--the osteoblasts and osteoclasts--are derived from different progenitor pools that are under distinct molecular control mechanisms. Together, these cells form temporary anatomical structures, called basic multicellular units, that execute bone remodeling. A number of stimuli affect bone turnover, including hormones, cytokines, and mechanical stimuli. All of these factors affect the amount and quality of the tissue produced. Mechanical loading is a particularly potent stimulus for bone cells, which improves bone strength and inhibits bone loss with age. Like other materials, bone accumulates damage from loading, but, unlike engineering materials, bone is capable of self-repair. The molecular mechanisms by which bone adapts to loading and repairs damage are starting to become clear. Many of these processes have implications for bone health, disease, and the feasibility of living in weightless environments (e.g., spaceflight).