Important Determinant Of Bone Mass Research Articles

Nutrition, exercise, and bone status in youth.

The maximal amount of bone mass gained during growth (peak bone mass) is an important determinant of bone mass in later life and thereby an important determinant of fracture risk. Although genetic factors appear to be primary determinants of peak bone mass, environmental factors such as physical activity and nutrition also contribute. In this article, bone growth and maintenance are reviewed, and mechanisms are described whereby physical activity can affect bone mass. Studies addressing the effects of physical activity on bone status in youth are reviewed: Although conclusive data are not yet available, considerable evidence supports the importance of activity, especially activity initiated before puberty. The critical role of energy in bone growth is outlined, and studies assessing the impact of calcium intake during childhood and adolescence are reviewed. Although results of intervention trials are equivocal, other evidence supports a role for calcium intake during growth. Recommendations for physical activity and nutrition, directed to children and adolescents, are presented.

CALCIUM INTAKE PREDICTS BONE MINERAL DENSITY IN COMPETITIVE FEMALE RUNNERS579

In an effort to define predictors of bone mineral density in competitive female runners, 28 eumenorrheic women (age 24.4±4) were assessed for bone density, body composition, dietary intake, serum IGF-1 and running mileage. Bone mineral density (g/cm2) of the lumbar spine (LSBMD), femoral neck (FBMD), total hip (TBMD), whole body (WBMD) and body composition(%fat) were measured by dual energy x-ray absorptiometry (Hologic QDR-1000/W). Serum samples of IGF-1 (ng/mL) were analyzed by RIA. Daily dietary intake of total calories (Kcals), calcium (Cal, mg) and protein (Pro, g) were assessed by a four day diet record. Weekly average running mileage (Miles) was obtained in combination from self reports and analysis of training logs. Mean and standard deviations for all variables are presented below:Table Multiple regression analysis revealed that calcium intake explained 56% of the variance in femoral neck BMD and 55% in spine BMD (p=.05). No other independent variables studied were found to correlate with bone mineral density. In conclusion, in this group of competitive female runners, calcium intake was an important determinant of bone mass at clinically relevant sites.

Can we detect women with low bone mass using clinical risk factors?

The magnitude of osteoporosis, the establishedrelationship between low bone mass and the risk of fracture, and the availability of preventive treatment suggest that the early detection of women with low bone mass is justified. The feasibility of population screening using bone mass measurements remains controversial. Another approach is the use of clinical risk factors to detect women at high risk. However, several studies have demonstrated that the assessment of risk factor status does not appear to be an efficient tool for the identification of perimenopausal women with low bone mass. The poor performance of the prediction models might be explained in part by unmeasured factors, especially genetic factors, which are an important determinant of bone mass. On the other hand, the clinical usefulness of clinical risk factors needs to be more precisely evaluated, especially in the detection of women at high risk for hip fracture.

Demonstration that bone mass is greater in black than in white children

Osteoporosis and hip fractures are less common and bone mass is greater in black than in white women. To determine if bone mass is greater in black than in white children, bone mineral density (BMD) of the midradius by single-photon absorptiometry and BMD of the lumbar spine (L1-L4), trochanter, and femoral neck by dual-photon absorptiometry were measured in 20 black boys, 18 black girls, 33 white boys, and 35 white girls between the ages of 7 and 12 years. Mean age (10.4 +/- 0.3 versus 10.2 +/- 0.2 years) and body weight (39 +/- 2 versus 38 +/- 2 kg) in the blacks and whites, respectively, were not different in the two groups, and the ages and weights of the boys and girls were not different from each other. BMD were significantly greater in black than in white children at each site, in the black than in white boys at the trochanter and femoral neck, and in the black than in white girls at each site. In both races, BMD varied directly with age and body weight. Multivariate analysis showed that BMD were greater at the midradius, lumbar spine, trochanter, and femoral neck in the black than in the white children, that BMD of the lumbar spine was greater in the girls than in the boys, and that BMD of the trochanter and femoral neck were greater in the boys than in the girls. There were significant partial correlations between race and BMD and between BMD and body weight at each site, between sex and BMD at the lumbar spine, trochanter, and femoral neck, and between age and BMD at the midradius, trochanter, and femoral neck. Race, sex, age, and body weight together accounted for 49-66% of the variation in bone mass. Thus, BMD of the midradius, spine, and hip are greater in black than in white children, body weight and age are important determinants of bone mass, and some sex differences in bone mass are present at this age.

Immobilization osteoporosis: a review.

Bone mass is not only subject to systemic hormonal homeostatic mechanisms, but also to local mechanical influences. The importance of the mechanical balance of bone has been more recently stressed by the research on the effect of weightlessness on bone, and by the introduction of the concept of "mechanostat" in the pathogenesis of osteoporotic conditions. Immobilization osteoporosis has clinical (fractures, sometimes hypercalcemia, urinary lithiasis) and radiological features. Immobilization has an effect on bone modeling and remodeling, through an increased activation of remodeling loci, and a decrease of the osteoblastic stimulus. This leads directly to a local reduction in bone mass, the increased activation multiplying the effect of the deficit in bone formation. The prevention is based on exercise if the load is applied intermittently for a daily period. It seems also that muscle weight is an important determinant of bone mass. There is a potential for recovery during the active early phase of immobilization osteoporosis that may disappear in the subsequent late (about six months) inactive phase. Permanent losses could be prevented by appropriate measures, pharmacology or exercises, applied during the first months of immobilization. No recovery has been demonstrated after the inactive phase has been reached, whatever the treatment. The cumulative effect of repeated periods of immobilization remains hypothetical.

The relationship between resorption depth and mean interstitial bone thickness: Age-related changes in man

The amounts of bone resorbed and formed in each bone remodelling unit are important determinants of bone mass. The mean wall thickness (MWT), which indicates the amount formed, decreases with age; less is known about changes in resorption depth although two studies have reported some evidence in favor of an age-related decrease. We have calculated mean intersitial bone thickness (MIBT), which is indirectly related to resorption depth, from measurements of MWT and mean trabecular plate thickness (MTPT) in 48 normal subjects, aged 19-80 years. No significant age-related changes in MIBT were found in either sex, or in both sexes grouped together, whereas MWT and MTPT showed a significant decrease with age (P less than 0.001 and less than 0.05 respectively). Detailed analysis of possible relationships between MIBT and resorption depth revealed that, assuming formation never exceeds resorption, a decreased MIBT may be associated with an increased, constant, or decreased resorption depth; an increased MIBT can only result from a decreased resorption depth. A constant MIBT may indicate either an unchanged or decreased resorption depth; in the former case, MTPT is unchanged whereas a decreased resorption depth is associated with a decreased MTPT. In view of the age-related reduction in MTPT, our results are therefore consistent with earlier reports of an age-related decrease in resorption depth. No evidence for an increased resorption depth during the menopause was found in this study.

The effects of muscle-building exercise on vitamin D and mineral metabolism.

Exercise and muscle strength are important determinants of bone mass. Studies were carried out in normal young adult white males to determine the effects of exercise on vitamin D and mineral metabolism. Fourteen men who had engaged in regular muscle-building exercises for at least 1 year and 14 age-matched controls (age range, 19-36 year) were hospitalized on a metabolic ward and were given a constant daily diet estimated to contain 400 mg of calcium, 900 mg of phosphorus, 110 mEq of sodium, 65 mEq of potassium, and 18 mEq of magnesium. Body weight averaged 78 +/- 3 kg in the exercisers and 72 +/- 2 kg in the controls (NS). Serum calcium, ionized calcium, phosphate, magnesium, somatomedin-C, and immunoreactive parathyroid hormone (PTH) were not different in the two groups, whereas serum Gla-protein (39 +/- 5 vs. 24 +/- 2 ng/ml, p less than 0.01), 25-hydroxyvitamin D (23 +/- 2 vs. 16 +/- 2, p less than 0.05) and 1,25-dihydroxyvitamin D [1,25(OH)2D] (40 +/- 2 vs. 29 +/- 2 pg/ml, p less than 0.01) were higher in the exercisers than in the controls. Urinary calcium, phosphorus, sodium, potassium, creatinine clearance, and norepinephrine were not different in the two groups, whereas urinary magnesium (12.6 +/- 1.0 vs. 9.4 +/- 0.5 mEq/d, p less than 0.01) and urinary cyclic adenosine 3',5'-monophosphate (cyclic AMP) (2.52 +/- 0.19 vs. 1.72 +/- 0.20 nM/dl glomerular filtrate, p less than 0.01) were higher in the exercisers than in the controls.(ABSTRACT TRUNCATED AT 250 WORDS)

Serum Calcitriol and Cigarette Smoking are Important Determinants of Bone Mass in Patients with Primary Hyperparathyroidism

Serum Calcitriol and Cigarette Smoking are Important Determinants of Bone Mass in Patients with Primary Hyperparathyroidism

Bone status and fracture rates in two regions of Yugoslavia

Bone status and fracture rates were evaluated in two Yugoslav populations with very different dietary habits. In district A (Podravina) the daily calcium intake was about twice that in district B (Istra). There were similar but smaller differences in the intakes of other nutrients. In district B metacarpal cortical width was reduced in all age groups of both sexes but the difference tended to decrease with age. The proximal femur fracture rate was higher in district B than district A but there was no difference between the forearm fracture rates in the two districts. Our results confirm that bone mass at any age is clearly the result of age and sex and most probably other genetically determined factors but also show that this expression is nutrition related. The data suggest that nutrition (in particular the calcium intake) is an important determinant of bone mass in young adults but seems to have little effect on age-related bone loss in either males or females. The main determinant of cortical bone mass in the elderly seems to be the cortical bone mass in middle life. The proximal femur fractures of old people reflect declining cortical bone mass but the distal forearm fractures of middle-aged women are unrelated to cortical bone mass or nutritional status.

RELATION BETWEEN BONE MASS AND MUSCLE WEIGHT

The ash weight of the third lumbar vertebral body and the weight of the left psoas muscle from forty-six routine necropsies were significantly correlated (p<0·001) when bodyweight, age, and height were taken into account. It is proposed that the weight of a muscle reflects the forces that it exerts on bones to which it is attached and that muscle weight is an important determinant of bone mass.