J. F. Aloia

Comparative skeletal mass and radial bone mineral content in black and white women

The age-related changes in both skeletal mass and muscle mass were directly measured in normal black women ages 30-80 yr. The levels of total-body calcium (TBCa) were determined with the use of in vivo neutron activation. The muscle mass was measured by wholebody counting of 40K. In the same population, the bone mineral content of the radius was measured using a photon absorptiometric technique. Although there was no significant difference in stature, black women had a greater skeletal mass and bone mineral content of the radius than age-matched white female subjects. When the TBCa values were normalized for body size (i.e., corrected for height and lean body mass), the TBCa was still higher for the black women but not as high as the absolute TBCa values. Clearly, it is the larger muscle mass (as reflected by the 40K measure) in relation to weight and height that accounts for this difference. The lower prevalence of fracture and osteoporosis observed in black women relative to white women is due in part to this greater quantity of skeleton. American black women with a higher bone density (i.e., skeletal mass) maintain mechanical integrity of the skeleton longer than individuals with a lower bone density. It is suggested that the larger muscle mass in black women is, in part, a determinant of their increased skeletal mass and is partly responsible for their apparent resistance to osteoporosis and fracture of the skeleton.

Changes in body chemical composition with age measured by total-body neutron activation☆

Total-body levels of calcium and phosphorus (reflecting skeletal mass) and total-body levels of potassium (reflecting muscle mass) were measured by neutron activation analysis in 39 men and 40 women ages 30-90 yr. In order to intercompare the total body calcium (TBCa) values in a heterogeneous population, such as this, it was necessary to normalize the data for skeletal size. The normalization consisted of dividing the absolute calcium level by the predicted calcium level for each individual matched to a set of critical parameters. The parameter used in the computation of normal values were age, sex, muscle mass, i.e., total body potassium (TBK) and height. For the calcium data of the women, it was necessary to add an age correction factor after the age of 55 yr. The calcium ratio(mean ratio of the predicted to measured TBCa) in men was 1.000 +/- 7.8% and in women 0.996 +/- 7.1%. The TBCa of normal males and females can thus be predicted to +/- 13% (at the 90% confidence level). An exception to this was found in males (70-90 yr) who exhibited a mean calcium ratio greater than 1.13. The derivative of TBCa with time was determined for this population of men and women by taking into account the dependency of calcium on three time dependent variables, height, TBK, and an explicit age correction factor in the case of the women. The mean rate of loss of TBCa in women was 0.37% and 1.1% per year before and after menopause (50 yr). In the males, the average rate of loss of TBCa was 0.7% per year after 50 yr of age. The pattern of total body phosphorus (TBP) loss with age paralleled that of TBCa as the ratio of TBP/TBCa was rather constant with age. The constancy of the ratio suggests that the mineral composition of bone does not change significantly with age. The rate of loss of TBK with age was also related directly to that of TBCa. The mean ratio of TBK/TBCa was 9.9 in females and 8.0 in males and this ratio remained relatively constant from 30-70 yr. Thus, the mechanism responsible for the loss of bone with age, whether nutritional deficiency or decreased gonadal function and physical activity may also be responsible for the loss of muscle mass with age.

Skeletal mass and body composition in marathon runners

Skeletal and lean body mass was measured in 30 male marathon runners and in 16 subjects of comparable ages who were relatively sedentary. Skeletal mass was measured by total body neutron activation analysis (total body calcium—TBCa) and photon absorptiometry of the distal radius (bone mineral content—BMC). Lean body mass was estimated by the measurement of 40K in a whole body counter (total body K—TBK). The marathon runners were slightly taller and lighter than the contrast group; the bone width of the radius was essentially the same for both groups. When the values for TBK and TBCa were corrected for age and body size, the marathon runners were found to have values that were 7% (p < .002) and 11% (p < .001) higher, respectively. The values of BMC were somewhat elevated in the marathon runners but this increase in regional bone mass was not statistically significant. These data suggest that marathon running may be associated with prevention of the changes that occur in body composition with aging and raise the possibility that exercise may prevent the involutional loss of skeletal and lean body mass.

Comparison of body composition in black and white premenopausal women

We examined 23 pairs of black and white premenopausal women to determine whether there were ethnic differences in body composition. The pairs were matched on weight and height. Each woman had measurements of total body water taken by a tritiated water dilution technique, total body nitrogen, and total body carbon by neutron-activation, mineral ash by dual x-ray absorptiometry, and body potassium by whole body counting. Differences between blacks and whites were compared with the use of both the two-compartment and four-compartment models. The two-compartment model showed that in premenopausal black and white women of similar age, heights, and weights, blacks had significantly more lean mass. The four-compartment model resulted in similar conclusions. The black women had larger protein, mineral, and water compartments and less fat than whites. It may be that body weight measurements as an indicator of obesity should be adjusted for black versus white women.

Aging in women—the four-compartment model of body composition

The four-compartment model of body composition was examined in 155 white women through measurement of total body carbon (TBC), nitrogen (TBN), calcium (TBCa), and water levels. The age (mean +/- SD) of the population was 51.4 +/- 13.5 years, and values for the four compartments were as follows (in kilograms): protein 8.9 +/- 1.0, water 30.9 +/- 3.5, mineral 2.6 +/- 0.4, and fat 22.6 +/- 7.3. There was a linear change with age for protein and water, whereas mineral and fat were curvilinear. These latter two compartments also showed differences in premenopausal and postmenopausal rates of change. Various models were fit to the data to adjust for body size and age. Each of the four compartments (mineral, water, fat, and protein) changed with age, with fat increasing and the other compartments declining. The equation, y = age + age2 + height + weight, fit the data as well as the other models. Equations are provided to assess body composition in populations with disorders of nutrition, as well as other illnesses, using height, weight, and age as covariates. Since this was a cross-sectional study, longitudinal studies will have to be performed to confirm the accuracy of rates of change with age predicted with each compartment.

Relationship of body water compartments to age, race, and fat-free mass

Water compartments were studied in 72 black and 128 white women, aged 20 to 70 years. Total body water (TBW) was measured by tritiated water dilution, and extracellular water (ECW) was measured by using delayed gamma neutron activation for the determination of total body chloride. Intracellular water (ICW) was assessed as the difference between TBW and ECW. Fat-free mass (FFM) was estimated by the measurement of total body potassium (TBK) and total body fat (TBF) by measurement of total body carbon (TBC). Total body protein was calculated from total body nitrogen (TBN). TBW was found to decline with age and to also be significantly influenced by body size. The extracellular water space was 41.5% of TBW. The decline of TBW with age is due primarily to a decline in ICW. The hydration of the FFM increased with age for the overall population because of a decline in TBK and TBN and an increase in ECW. Body composition models that have assumed constancy of hydration should be adjusted not only for gender but for age and body size.

Absence of an effect of chronic administration of growth hormone on serum lipids

Human growth hormone (hGH) was administered to a group of osteoporotic patients at two dosage levels for a period of 6 mo each. The first dose employed was 2 units subcutaneously daily, and the second dose was 0.2W-3/4 units (where W is body weight expressed in kg) daily. There was no significant change in serum-cholesterol or triglyceride concentration despite the production of hyperglycemia and soft-tissue swelling on the higher dosage regimen. A number of factors may account for the conflict between our findings and a previous report in which hGH administration had a lypocholesterolemic, hyperglyceridemic effect. These factors include differences in sex, age, dosage, and duration of treatment. Nonetheless, it is clear that from a therapeutic vantage, even if hGH were readily available, it would not be a useful hypocholesterolemic agent.

Total-body calcium estimated by delayed gamma neutron activation analysis and dual-energy X-ray absorptiometry

Abstract: Total body calcium (TBCa) in 270 black and white women age 21–79 years was measured concurrently by delayed gamma neutron activation analysis (DGNA) and dual-energy X-ray absorptiometry (DXA). The mean value for TBCa calculated from DXA was 933 g compared with 730 g for DGNA. By regression, TBCaDXA(g)= 1.35 × TBCaDGNA(g)−54 (r= 0.90, r2= 81.4%, SEE = 66.9 g). This remarkable difference of 203 g suggests that one or both these methods is not accurate. Adjustment of the regression of DXA versus DGNA for body mass index or trunk thickness explained 8.5–10% of the variability between methods. The unadjusted slope for the DXA values regressed against the DGNA values was 1.35, indicating significant discordance between the methods. There is greater agreement between the two DGNA facilities (Brookhaven National Laboratory and Baylor College of Medicine) and between the various DXA instruments. Either DGNA underestimates TBCa or DXA overestimates total-body bone mineral content. Resolution of these disparate results may possibly be achieved by concurrent measurement of whole human cadavers of different sizes with chemical determination of the calcium content of the ash. In the interim, cross-calibration equations between DGNA and standardized values for DXA for total-body bone mineral content may be used, which will permit reporting of consistent values for TBCa from the two technologies.