Robin M. Daly

The effect of mechanical loading on the size and shape of bone in pre-, peri-, and postpubertal girls: a study in tennis players

Exercise during growth results in biologically important increases in bone mineral content (BMC). The aim of this study was to determine whether the effects of loading were site specific and depended on the maturational stage of the region. BMC and humeral dimensions were determined using DXA and magnetic resonance imaging (MRI) of the loaded and nonloaded arms in 47 competitive female tennis players aged 8–17 years. Periosteal (external) cross‐sectional area (CSA), cortical area, medullary area, and the polar second moments of area (IP, mm4) were calculated at the mid and distal sites in the loaded and nonloaded arms. BMC and IP of the humerus were 11–14% greater in the loaded arm than in the nonloaded arm in prepubertal players and did not increase further in peri‐ or postpubertal players despite longer duration of loading (both, p < 0.01). The higher BMC was the result of a 7–11% greater cortical area in the prepubertal players due to greater periosteal than medullary expansion at the midhumerus and a greater periosteal expansion alone at the distal humerus. Loading late in puberty resulted in medullary contraction. Growth and the effects of loading are region and surface specific, with periosteal apposition before puberty accounting for the increase in the bones resistance to torsion and endocortical contraction contributing late in puberty conferring little increase in resistance to torsion. Increasing the bones resistance to torsion is achieved by modifying bone shape and mass, not necessarily bone density.

Targeted exercise against osteoporosis: A systematic review and meta-analysis for optimising bone strength throughout life

BackgroundExercise is widely recommended to reduce osteoporosis, falls and related fragility fractures, but its effect on whole bone strength has remained inconclusive. The primary purpose of this systematic review and meta-analysis was to evaluate the effects of long-term supervised exercise (≥6 months) on estimates of lower-extremity bone strength from childhood to older age.MethodsWe searched four databases (PubMed, Sport Discus, Physical Education Index, and Embase) up to October 2009 and included 10 randomised controlled trials (RCTs) that assessed the effects of exercise training on whole bone strength. We analysed the results by age groups (childhood, adolescence, and young and older adulthood) and compared the changes to habitually active or sedentary controls. To calculate standardized mean differences (SMD; effect size), we used the follow-up values of bone strength measures adjusted for baseline bone values. An inverse variance-weighted random-effects model was used to pool the results across studies.ResultsOur quality analysis revealed that exercise regimens were heterogeneous; some trials were short in duration and small in sample size, and the weekly training doses varied considerably between trials. We found a small and significant exercise effect among pre- and early pubertal boys [SMD, effect size, 0.17 (95% CI, 0.02-0.32)], but not among pubertal girls [-0.01 (-0.18 to 0.17)], adolescent boys [0.10 (-0.75 to 0.95)], adolescent girls [0.21 (-0.53 to 0.97)], premenopausal women [0.00 (-0.43 to 0.44)] or postmenopausal women [0.00 (-0.15 to 0.15)]. Evidence based on per-protocol analyses of individual trials in children and adolescents indicated that programmes incorporating regular weight-bearing exercise can result in 1% to8% improvements in bone strength at the loaded skeletal sites. In premenopausal women with high exercise compliance, improvements ranging from 0.5% to 2.5% have been reported.ConclusionsThe findings from our meta-analysis of RCTs indicate that exercise can significantly enhance bone strength at loaded sites in children but not in adults. Since few RCTs were conducted to investigate exercise effects on bone strength, there is still a need for further well-designed, long-term RCTs with adequate sample sizes to quantify the effects of exercise on whole bone strength and its structural determinants throughout life.

Serum 25-hydroxyvitamin D, calcium intake, and risk of type 2 diabetes after 5 years: results from a national, population-based prospective study (the Australian Diabetes, Obesity and Lifestyle study).

OBJECTIVE To examine whether serum 25-hydroxyvitamin D (25OHD) and dietary calcium predict incident type 2 diabetes and insulin sensitivity. RESEARCH DESIGN AND METHODS A total of 6,537 of the 11,247 adults evaluated in 1999–2000 in the Australian Diabetes, Obesity and Lifestyle (AusDiab) study, returned for oral glucose tolerance test (OGTT) in 2004–2005. We studied those without diabetes who had complete data at baseline (n = 5,200; mean age 51 years; 55% were women; 92% were Europids). Serum 25OHD and energy-adjusted calcium intake (food frequency questionnaire) were assessed at baseline. Logistic regression was used to evaluate associations between serum 25OHD and dietary calcium on 5-year incidence of diabetes (diagnosed by OGTT) and insulin sensitivity (homeostasis model assessment of insulin sensitivity [HOMA-S]), adjusted for multiple potential confounders, including fasting plasma glucose (FPG). RESULTS During the 5-year follow-up, 199 incident cases of diabetes were diagnosed. Those who developed diabetes had lower serum 25OHD (mean 58 vs. 65 nmol/L; P < 0.001) and calcium intake (mean 881 vs. 923 mg/day; P = 0.03) compared with those who remained free of diabetes. Each 25 nmol/L increment in serum 25OHD was associated with a 24% reduced risk of diabetes (odds ratio 0.76 [95% CI 0.63–0.92]) after adjusting for age, waist circumference, ethnicity, season, latitude, smoking, physical activity, family history of diabetes, dietary magnesium, hypertension, serum triglycerides, and FPG. Dietary calcium intake was not associated with reduced diabetes risk. Only serum 25OHD was positively and independently associated with HOMA-S at 5 years. CONCLUSIONS Higher serum 25OHD levels, but not higher dietary calcium, were associated with a significantly reduced risk of diabetes in Australian adult men and women.

Prevalence of vitamin D deficiency and its determinants in Australian adults aged 25 years and older: a national, population‐based study

Objective  Vitamin D deficiency is recognized as a global public health problem, but the population‐based prevalence of deficiency and its determinants in Australian adults is not known. This study evaluated the vitamin D status of Australian adults aged ≥25 years and risk factors associated with vitamin D deficiency in this population.

Vitamin D and health in adults in Australia and New Zealand: a position statement

The prevalence of vitamin D deficiency varies, with the groups at greatest risk including housebound, community‐dwelling older and/or disabled people, those in residential care, dark‐skinned people (particularly those modestly dressed), and other people who regularly avoid sun exposure or work indoors. Most adults are unlikely to obtain more than 5%–10% of their vitamin D requirement from dietary sources. The main source of vitamin D for people residing in Australia and New Zealand is exposure to sunlight. A serum 25‐hydroxyvitamin D (25‐OHD) level of ≥ 50 nmol/L at the end of winter (10–20 nmol/L higher at the end of summer, to allow for seasonal decrease) is required for optimal musculoskeletal health. Although it is likely that higher serum 25‐OHD levels play a role in the prevention of some disease states, there is insufficient evidence from randomised controlled trials to recommend higher targets. For moderately fair‐skinned people, a walk with arms exposed for 6–7 minutes mid morning or mid afternoon in summer, and with as much bare skin exposed as feasible for 7–40 minutes (depending on latitude) at noon in winter, on most days, is likely to be helpful in maintaining adequate vitamin D levels in the body. When sun exposure is minimal, vitamin D intake from dietary sources and supplementation of at least 600 IU (15 μg) per day for people aged ≤ 70 years and 800 IU (20 μg) per day for those aged > 70 years is recommended. People in high‐risk groups may require higher doses. There is good evidence that vitamin D plus calcium supplementation effectively reduces fractures and falls in older men and women.

Low serum 25-hydroxyvitamin D is associated with increased risk of the development of the metabolic syndrome at five years: results from a national, population-based prospective study (The Australian Diabetes, Obesity and Lifestyle Study: AusDiab).

CONTEXT Serum 25-hydroxyvitamin D [25(OH)D] concentration has been inversely associated with the prevalence of metabolic syndrome (MetS), but the relationship between 25(OH)D and incident MetS remains unclear. OBJECTIVE We evaluated the prospective association between 25(OH)D, MetS, and its components in a large population-based cohort of adults aged 25 yr or older. DESIGN We used baseline (1999-2000) and 5-yr follow-up data of the Australian Diabetes, Obesity, and Lifestyle Study (AusDiab). PARTICIPANTS Of the 11,247 adults evaluated at baseline, 6,537 returned for follow-up. We studied those without MetS at baseline and with complete data (n = 4164; mean age 50 yr; 58% women; 92% Europids). OUTCOME MEASURES We report the associations between baseline 25(OH)D and 5-yr MetS incidence and its components, adjusted for age, sex, ethnicity, season, latitude, smoking, family history of type 2 diabetes, physical activity, education, kidney function, waist circumference (WC), and baseline MetS components. RESULTS A total of 528 incident cases (12.7%) of MetS developed over 5 yr. Compared with those in the highest quintile of 25(OH)D (≥34 ng/ml), MetS risk was significantly higher in people with 25(OH)D in the first (<18 ng/ml) and second (18-23 ng/ml) quintiles; odds ratio (95% confidence interval) = 1.41 (1.02-1.95) and 1.74 (1.28-2.37), respectively. Serum 25(OH)D was inversely associated with 5-yr WC (P < 0.001), triglycerides (P < 0.01), fasting glucose (P < 0.01), and homeostasis model assessment for insulin resistance (P < 0.001) but not with 2-h plasma glucose (P = 0.29), high-density lipoprotein cholesterol (P = 0.70), or blood pressure (P = 0.46). CONCLUSIONS In Australian adults, lower 25(OH)D concentrations were associated with increased MetS risk and higher WC, serum triglyceride, fasting glucose, and insulin resistance at 5 yr. Vitamin D supplementation studies are required to establish whether the link between vitamin D deficiency and MetS is causal.

Effects of High-Impact Exercise on Ultrasonic and Biochemical Indices of Skeletal Status: A Prospective Study in Young Male Gymnasts

Physical activity has been proposed as one strategy to enhance bone mineral acquisition during growth. The aim of this study was to determine whether frequent impact loading associated with gymnastics training confers a skeletal benefit on pre‐ and peripubertal male gymnasts. We measured broadband ultrasonic attenuation (BUA, dB/MHz) at the calcaneus (CBUA); ultrasound velocity (m/s) at the calcaneus (CVOS), distal radius (RVOS) and phalanx (PVOS); serum osteocalcin (OC); total alkaline phosphatase (ALP) and insulin‐like growth factor‐I (IGF‐I) every 3–4 months over an 18‐month period in elite male gymnasts and matched normoactive controls (pubertal stage ≤2). Ground reaction forces of common gymnastics maneuvers were determined using a force platform and loading histories of the upper and lower extremities approximated from video recordings. Ultrasound results were expressed as a standardized score (Z score) adjusted for age, height, and weight. At baseline, no differences were detected between the gymnasts (n = 31) and controls (n = 50) for CBUA, although ultrasound velocity at each site was higher in the gymnasts (0.6–1.5 SD) than the predicted mean in controls (p ≤ 0.001). Over 18 months, CBUA Z scores increased significantly in the gymnasts from baseline (0.3 vs. 1.0, p < 0.05, n = 18). In contrast, ultrasound velocity did not increase in either group, although CVOS and RVOS remained significantly higher in gymnasts compared with controls (range p < 0.01 and < 0.001). No differences between groups were found for OC, ALP, or IGF‐I at any time. Gymnastics training was associated with on average 102 and 217 impacts per session on the upper and lower extremities, respectively, with peak magnitudes of 3.6 and 10.4 times body weight. These results suggest that frequent high‐impact, weight‐bearing exercise during the pre and peripubertal period may enhance the mechanical competence of the skeleton, perhaps offering an important strategy for osteoporosis prevention if the benefits are maintained.

Calcium‐ and Vitamin D3‐Fortified Milk Reduces Bone Loss at Clinically Relevant Skeletal Sites in Older Men: A 2‐Year Randomized Controlled Trial

In this 2‐year randomized controlled study of 167 men >50 years of age, supplementation with calcium‐vitamin D3‐fortified milk providing an additional 1000 mg of calcium and 800 IU of vitamin D3 per day was effective for suppressing PTH and stopping or slowing bone loss at several clinically important skeletal sites at risk for fracture.

The Effect of Exercise on Bone Mass and Structural Geometry during Growth

Regular weight-bearing exercise is widely reported to have beneficial effects on bone mineral content and areal bone mineral density during growth, but the structural basis underlying these changes remains uncertain. In young athletic children, participation in high-impact sports has been shown to enhance bone formation on the periosteal and/or endosteal surfaces of long bones at loaded skeletal sites. Participation in moderate physical activity, recreational play or school-based exercise interventions designed to specifically load bone have also been shown to enhance bone mineral accrual. However, few data are available on the surface-specific effects of exercise training or general physical activity on bone. Based on the limited data available, it would appear that the structural response of bone to exercise during growth is maturity dependent and sex specific; prior to puberty exercise appears to increase periosteal apposition in both sexes, whereas during or late in puberty exercise appears to result in periosteal expansion in boys but endocortical contraction in girls. In most cases, these geometric changes lead to an increase in bone bending strength. However, there are contrasting results as to whether the pre- or peripubertal years are an optimal time to intervene for the greatest osteogenic response; it is likely that both periods represent an important time for incorporating physical activity to optimize bone health. There are also many unresolved questions as to the optimal dose of exercise (intensity, frequency, duration and rate of progression) needed to enhance bone strength in children and adolescents. We know that weight-bearing exercise is important, and that activities should be dynamic, variable in nature, applied rapidly and intermittently, and that relatively few loading cycles are required. Although several effective interventions have been designed for improving bone mass, further research is needed to define the specific exercise programs or activities that will optimize bone structure and strength during growth. Perhaps most importantly, further work is also needed to determine whether any exercise-induced alterations in bone mass and structure during growth are maintained into old age when fractures occur.

Effects of resistance exercise and fortified milk on skeletal muscle mass, muscle size, and functional performance in middle-aged and older men: an 18-mo randomized controlled trial

Limited data have suggested that the consumption of fluid milk after resistance training (RT) may promote skeletal muscle hypertrophy. The aim of this study was to assess whether a milk-based nutritional supplement could enhance the effects of RT on muscle mass, size, strength, and function in middle-aged and older men. This was an 18-mo factorial design (randomized control trial) in which 180 healthy men aged 50-79 yr were allocated to the following groups: 1) exercise + fortified milk, 2) exercise, 3) fortified milk, or 4) control. Exercise consisted of progressive RT with weight-bearing impact exercise. Men assigned to the fortified milk consumed 400 ml/day of low-fat milk, providing an additional 836 kJ, 1000 mg calcium, 800 IU vitamin D(3), and 13.2 g protein per day. Total body lean mass (LM) and fat mass (FM) (dual-energy X-ray absorptiometry), midfemur muscle cross-sectional area (CSA) (quantitative computed tomography), muscle strength, and physical function were assessed. After 18 mo, there was no significant exercise by fortified milk interaction for total body LM, muscle CSA, or any functional measure. However, main effect analyses revealed that exercise significantly improved muscle strength ( approximately 20-52%, P < 0.001), LM (0.6 kg, P < 0.05), FM (-1.1 kg, P < 0.001), muscle CSA (1.8%, P < 0.001), and gait speed (11%, P < 0.05) relative to no exercise. There were no effects of the fortified milk on muscle size, strength, or function. In conclusion, the daily consumption of low-fat fortified milk does not enhance the effects of RT on skeletal muscle size, strength, or function in healthy middle-aged and older men with adequate energy and nutrient intakes.