Increasing weight-bearing physical activity and calcium intake for bone mass growth in children and adolescents: a review of intervention trials

Parental safety concerns--a barrier to sport and physical activity in children?

OBJECTIVE

To examine the extent to which parents and carers perceive injury and safety risks as serious enough to prevent or discourage their children, aged 5-12 years, from participating in sports/physical activity and to identify factors that influence these perceptions.

METHODS

An analysis of the 2001 New South Wales Child Health Survey.

RESULTS

More than one-quarter of parents/ carers of active children aged 5-12 years reported discouraging or preventing children from playing a particular sport (34.7% for boys and 16.6% for girls) because of injury and safety concerns. In boys, the most frequently discouraged sport was rugby league (23.2%), followed by rugby union (7.5%) and Australian rules football (2.8%). Among girls, the most frequently discouraged activities were rollerblading (2.7%), rugby league (2.3%) and soccer (2.1%). Multivariate analysis shows that factors independently associated with parents' decision to prevent/discourage their child from engaging in sport/physical activity include their child's age and gender, language spoken at home, presence of disability, and the respondent's relation to the child.

CONCLUSIONS AND IMPLICATIONS

Efforts need to be made to modify some sports/ activities, such as football codes, in order to minimise injury and to ensure that children continue enjoying their favourite activity well into adulthood. Guidelines designed to promote physical activity among children and young adolescents need to take into account parental concerns regarding the associated risk of injury.

Health-enhancing physical activity and sedentary behaviour in children and adolescents

We provide a wide-ranging review of health-related physical activity in children and adolescents using a behavioural epidemiology framework. In contrast to many other reviews, we highlight issues associated with true sedentary behaviours alongside physically active behaviours. Specifically, we review the evidence concerning the links between physical activity and cardiovascular disease, overweight and obesity, psychosocial measures, type II diabetes, and skeletal health. Although the evidence is unconvincing at times, several factors lead to the conclusion that promoting physical activity in youth is desirable. A review of the prevalence of physical activity and sedentary behaviours shows that many young people are active, but this declines with age. A substantial number are not adequately active for health benefits and current trends in juvenile obesity are a cause for concern. Prevalence data on sedentary behaviours are less extensive but suggest that total media use by young people has not changed greatly in recent years. Most children and adolescents do not exceed recommended daily hours of TV viewing. Physical activity is unrelated to TV viewing. We also identified the key determinants of physical activity in this age group, highlighting demographic, biological, psychological, behavioural, social and environmental determinants. Interventions were considered for school, family and community environments. Finally, policy recommendations are offered for the education, governmental, sport and recreation, health, and mass media sectors.

Positive, site-specific associations between bone mineral status, fitness, and time spent at high-impact activities in 16- to 18-year-old boys

The incidence of hip and forearm fracture in elderly men in the United Kingdom is a public health issue, but there is limited knowledge on lifestyle factors affecting male bone health. The aim of this cross-sectional study was to evaluate the relationships between whole body and regional bone mineral status and self-reported participation time in no-, low-, moderate-, and high-impact activities and fitness measurements in 16- to 18-year-old boys. One hundred twenty-eight boys underwent absorptiometry (DXA) measurements (Hologic QDR 1000W) of bone mineral content (BMC), bone area (BA), and bone mineral density (BMD) at the whole body, hip, spine, and forearm. They also completed the EPIC (European Prospective Investigation of Cancer) physical activity questionnaire, which allowed categorization of activities according to impact and aerobic intensity. Fitness and strength were assessed in each subject using estimated VO2 max, grip strength, and back strength. Significant positive relationships were found between BMC, BA, and BMD and the fitness and strength measurements and participation time in high-impact sports at most skeletal sites. The relationships were further examined after adjustment of BMC for height, weight, and bone area, thereby minimizing the influence of body and bone size on these relationships. VO2 max was a significant positive determinant of size-adjusted BMC at the whole body, the ultradistal and one-third radius, and all the hip sites, except the trochanter. Size-adjusted BMC at the forearm sites and trochanter was significantly positively associated with grip strength. Size-adjusted BMC at the whole body and all the hip sites was significantly positively associated with time spent at high-impact activities. Differences in size-adjusted BMC across thirds of time spent at high-impact activities were also examined. Boys in the highest third of high-impact activity had significantly greater size-adjusted whole body BMC and total hip BMC compared to subjects in the lowest third [+3.4 (1.2)% for whole body and +8.5 (2.2)% for hip, both P = 0.001]. Boys in the highest third of high-impact activity spent most activity time jogging, playing tennis, football and rugby, basketball, and exercising with weights. Back strength and lean mass were significantly greater in subjects in the highest third compared to those in the middle (P = 0.02) and lowest third (P = 0.03). No significant differences were found between subjects in each third of high-impact activity for potential confounders including TV viewing, calcium intake, body fat, and height. These findings indicate that participation of male adolescents in a range of high-impact activities for 1 h or more a day is associated with greater bone size and mineral content, especially at the hip.

Bone outcomes and technical measurement issues of bone health among children and adolescents: considerations for nutrition and physical activity intervention trials

Weight-bearing physical activity and calcium intake are two important behavioral influences for bone health. Physical-activity and calcium-intake intervention trials with youth have been implemented to evaluate their efficacy and effectiveness to decrease the risk for subsequent osteoporosis and fractures. Technical aspects of bone measurement have not been routinely reported in published trials of youth, even though they can have an impact on study findings and interpretation. This paper provides an overview of the outcome variables reported, and technical issues--such as software and bone detection, growth, and movement--that affect bone mass measurements among children and adolescents. It describes the implications of these issues for the interpretation of intervention effects observed in intervention trials, and provides recommendations for future research.

Adolescent dairy consumption and physical activity associated with bone mass

BACKGROUND

This study identifies key modifiable factors influencing Asian and White adolescent bone development. Cross-sectional analysis of baseline data of cohort.

METHODS

Three hundred and twenty-three girls were examined from age-eligible girls at Kaiser Permanente Oahu in Hawaii. Girls' age, ethnicity, Tanner stage, 3-day diet record, level of physical activity, anthropometry, and calcaneal bone status were obtained by questionnaire and measurement, respectively. Lunar Achilles calcaneal was used to measure calcaneal bone mass. Multiple regression was used for analysis of factors influencing bone mass.

RESULTS

The mean age of adolescents was 11.6 +/- 1.5 years. Girls were generally ethnically mixed; the mean Asian ethnic proportion was 48% while White ethnic proportion was 43% and other ethnic proportion was 10%. Multiple regression explained 40.8% and 25.6% of the variation in calcaneal broadband ultrasound attenuation (BUA) and speed of sound (SOS), respectively, in a model where age, weight, biacromial breadth, Tanner pubic hair stage, Asian ethnicity, dairy intake, and physical activity positively influenced bone mass.

CONCLUSIONS

Tanner pubic hair stage, ethnicity, and biacromial breadth had the greatest influence on SOS; while physical activity, body weight, and dairy product intake had the greatest influence on BUA.

A pilot intervention to increase calcium intake in female collegiate athletes

Calcium intake in adolescent and young adult female athletes often is inadequate to optimize peak bone mass, an important determinant of osteoporosis risk. The purpose of this study was to determine if calcium supplementation in eumenorrheic female collegiate athletes increases intake to recommended levels and promotes increases in bone mineral density (BMD). Forty-eight eumenorrheic female athletes from several college teams (15 soccer, 7 cross-country, 8 indoor track, and 18 basketball) were randomized at the beginning of a competitive season to receive either an oral calcium supplement (1000 mg calcium citrate/400 I.U. Vitamin D) or placebo daily throughout the training season (16 weeks). Self-reported daily pill intake was obtained every 2 weeks to assess adherence. Calcium intake was evaluated using the Rapid Assessment Method, and total body and leg BMD was measured at pre-, mid-, and postseason using dual energy x-ray absorptiometry (DEXA; Hologic QDR-2000). Pre-season calcium intake was lower than national recommendations for this age group (12), averaging 842 mg/d (SD = 719) and was lower in the placebo group compared to the supplemented group (649 +/- 268 vs. 1071 +/- 986 mg/d, respectively; p = .064). Adherence to supplementation was good, averaging 70% across the training season. Supplementation boosted total calcium intake to a mean of 1397 +/- 411 mg/d, which is consistent with recommended levels for this group (37). Supplementation did not influence BMD change during this 16-week intervention. Across teams, a small increase of 0.8% was observed in leg BMD. Change in total body BMD was modified by team, with a significant increase of 1.5% observed in basketball players. These results indicate that providing calcium supplements of 1000 mg/d is adequate to boost total intake to recommended levels during athletic training. Longer intervention trials are required to determine whether calcium supplementation has a positive effect on BMD.

The aging of Wolff's ?law?: Ontogeny and responses to mechanical loading in cortical bone

The premise that bones grow and remodel throughout life to adapt to their mechanical environment is often called Wolff's law. Wolff's law, however, is not always true, and in fact comprises a variety of different processes that are best considered separately. Here we review the molecular and physiological mechanisms by which bone senses, transduces, and responds to mechanical loads, and the effects of aging processes on the relationship (if any) between cortical bone form and mechanical function. Experimental and comparative evidence suggests that cortical bone is primarily responsive to strain prior to sexual maturity, both in terms of the rate of new bone growth (modeling) as well as rates of turnover (Haversian remodeling). Rates of modeling and Haversian remodeling, however, vary greatly at different skeletal sites. In addition, there is no simple relationship between the orientation of loads in long bone diaphyses and their cross-sectional geometry. In combination, these data caution against assuming without testing adaptationist views about form-function relationships in order to infer adult activity patterns from skeletal features such as cross-sectional geometry, cortical bones density, and musculo-skeletal stress markers. Efforts to infer function from shape in the human skeleton should be based on biomechanical and developmental models that are experimentally tested and validated.

Decreased bone ultrasound velocity in large-for-gestational-age infants

BACKGROUND

Bone speed of sound is a measure of bone breakability. There are few reports on bone mineral content in large for gestational age infants; most of them in infants of diabetic mothers. There are no data on bone speed of sound in large for gestational age infants of nondiabetic mothers.

OBJECTIVE

To test the hypothesis that large for gestational age infants of nondiabetic mothers have lower bone speed of sound than appropriate for gestational age infants.

DESIGN/METHODS

Bone speed of sound was measured within the first 96 hours of life at the right tibial midshaft in 25 singleton large for gestational age infants of non diabetic mothers and compared to appropriate for gestational age controls.

RESULTS

Bone speed of sound measured in large for gestational age infants of nondiabetic mothers was lower than in controls.

CONCLUSIONS

Large for gestational age infants of nondiabetic mothers have lower bone speed of sound than controls.

Children who avoid drinking cow milk have low dietary calcium intakes and poor bone health

BACKGROUND

Information concerning the adequacy of bone mineralization in children who customarily avoid drinking cow milk is sparse.

OBJECTIVE

The objective was to evaluate dietary calcium intakes, anthropometric measures, and bone health in prepubertal children with a history of long-term milk avoidance.

DESIGN

We recruited 50 milk avoiders (30 girls, 20 boys) aged 3-10 y by advertisement. We measured current dietary calcium intakes with a food-frequency questionnaire and body composition and bone mineral density with dual-energy X-ray absorptiometry and compared the results with those of 200 milk-drinking control children.

RESULTS

The reasons for milk avoidance were intolerance (40%), bad taste (42%), and lifestyle choice (18%). Dietary calcium intakes were low (443 +/- 230 mg Ca/d), and few children consumed substitute calcium-rich drinks or mineral supplements. Although 9 children (18%) were obese, the milk avoiders were shorter (P < 0.01), had smaller skeletons (P < 0.01), had a lower total-body bone mineral content (P < 0.01), and had lower z scores (P < 0.05) for areal bone mineral density at the femoral neck, hip trochanter, lumbar spine, ultradistal radius, and 33% radius than did control children of the same age and sex from the same community. The z scores for volumetric (size-adjusted) bone mineral density (g/cm(3)) were -0.72 +/- 1.17 for the lumbar spine and -0.72 +/- 1.35 for the 33% radius (P < 0.001). Twelve children (24%) had previously broken bones.

CONCLUSIONS

In growing children, long-term avoidance of cow milk is associated with small stature and poor bone health. This is a major concern that warrants further study.

Four-year gain in bone mineral in girls with and without past forearm fractures: a DXA study. Dual energy X-ray absorptiometry

We have previously shown that girls with a recent distal forearm fracture have weaker skeletons than girls who have never fractured. This could be a transient or persistent phenomenon. The present study was undertaken to determine whether the bone mineral content (BMC) of girls with previous distal forearm fractures remains lower 4 years postfracture or if catch-up gain has occurred. We report baseline and follow-up dual energy X-ray absorptiometry (DXA) results for 163 girls: 81 girls from the original control group who remained free of fracture (group 1) and 82 girls from the original group with distal forearm fractures (group 2). In data adjusted for bone area, height, weight, and pubertal status, group 2 girls had 3.5-8.5% less BMC at the total body, lumbar spine, ultradistal radius, and hip trochanter than group 1 at baseline, and 2.4-5.7% less BMC at these sites at follow-up. Even girls from group 2 who did not experience another fracture after baseline (n = 58) did not display greater BMC at follow-up compared with baseline values at any site, indicating that the decreased BMC at the time of fracture had persisted. In group 2, the relative gain in BMC after adjusting for the initial BMC and current bone area, height, weight, and pubertal stage was less than or similar to, but not greater than that of group 1 (ratio [95% CI]: total body, 0.985 [0.972-0.998]; lumbar spine, 0.961 [0.935-0.987]; ultradistal radius, 0.968 [0.939-0.998]; hip trochanter, 0.955 [0.923-0.988]; femoral neck, 0.981 [0.956-1.007]; and 33% radius 0.999 [0.977-1.021]). These findings indicate that girls with distal forearm fractures do not improve their gain of BMC. We conclude that girls who have sustained a distal forearm fracture maintain their lower BMC at most sites for at least 4 years.