Jocelyn Walters

Postnatal Development of Bone Mineral Status During Infancy

OBJECTIVE To determine postnatal development in bone mineral status and its relationship to anthropometric measurements and other physiologic variables during the first year. METHODS Cross-section observational study of total body bone mineral content (TB BMC) and density (TB BMD) of 130 healthy infants (71 male and 59 female with 63 white and 67 African American) between 1 and 391 days. Whole body dual energy X ray absorptiometry (DXA) scans were performed on unsedated infants using a bone densitometer with pediatric platform. Scan analyses were performed with software version V5.64P. The ability of study independent variables to explain variance in bone mineral status was determined by multiple linear regression analysis. RESULTS During infancy, average TB BMC increased by 389% and TB BMD increased by 157%. The best determinant of bone mineral status is body weight which accounted for 97% of TB BMC, 98% of TB area and 86% of TB BMD variation. Postnatal age and body length jointly added only 1%, < 1% and 2.5%, respectively, to the explained variation of these DXA measurements; race, gender and season all failed to reach statistical significance. CONCLUSION In healthy infants, body weight is the dominant predictor of bone mineral status. The percent increase in TB BMC differs from increase in TB BMD. Normative data generated from this study would be useful in the identification of abnormal bone mineral status in infants.

Body Composition in Neonates: Relationship Between Measured and Derived Anthropometry with Dual-Energy X-Ray Absorptiometry Measurements

This study examined the relationship between measured and derived anthropometric measurements with dual-energy x-ray absorptiometry measured lean and fat mass at 3.0 ± 2.8 (SD) days in 120 neonates with birth weights appropriate (AGA; n = 74), large (LGA; n = 30); or small (SGA, n = 16) for gestational age. Anthropometric measurements, including total body weight and length, and regional measurements, including circumferences of head, chest, abdomen, midarm, and midthigh and dynamic skinfold thickness (15 and 60 s) at tricep, subscapular, suprailiac, and midthigh, were performed. Derived anthropometry included muscle and fat areas, and ratios were calculated from direct measurements. The skinfold thickness measurements between 15 and 60 s were highly correlated (r = 0.973–0.996, p < 0.001 for all comparisons). Strong correlations existed within the four circumferences of trunk and extremities, the four skinfolds, and the ratios of weight to length and its higher powers. Weight and length accounted for >97% of the variance of lean mass in AGA and SGA infants and 46% of the variance in LGA infants and for 80, 82, and 84% of the variance of fat mass in SGA, AGA, and LGA infants, respectively, whereas midarm:head circumference ratio and arm muscle and fat areas are the most important derived anthropometry in the prediction for body composition. They independently accounted for up to 16.5 and 10.2%, respectively, of the variance in body composition depending on the state of in utero growth. Thus, total body weight and length and some selected regional and derived anthropometry accounted for the vast majority of the variance of body composition.

Growth, Tolerance and Biochemical Measures in Healthy Infants Fed a Partially Hydrolyzed Rice Protein-Based Formula: A Randomized, Blinded, Prospective Trial

Objective: To evaluate growth, tolerance and plasma biochemistries in infants fed an experimental rice protein-based infant formula. Design: Randomized, blinded, 16 week parallel feeding trial of 65 healthy infants fed either an experimental partially hydrolyzed rice protein-based infant formula fortified with lysine and threonine (RPF, n = 32), or a standard intact cow’s milk protein-based formula (CMF, n = 33) as a control. Assessments occurred at enrollment (average 2 days), 2, 4, 8, and 16 weeks of age. Results: Growth as indicated by weight, length, and head circumference was not different between the 2 formula groups. All plasma biochemistries for both groups were within reference normal range. However, RPF group had lower phosphorus and urea nitrogen, lower essential amino acids except threonine, which was higher, and lower ratio of essential (including semi-essential) to non-essential amino acids. Differences in the concentrations and ratios of amino acids became less as feeding progressed with age. Plasma total protein, albumin, prealbumin, calcium, magnesium, and alkaline phosphatase were not different between groups. Conclusion: Healthy infants fed an experimental partially hydrolyzed rice protein-based formula had normal growth, tolerance, and plasma biochemistry comparable to those of infants fed a standard intact milk protein-based formula, despite some differences in amino acid profiles.

Effect of Hand Dominance on Bone Mass Measurement in Sedentary Individuals

The aim of this study was to determine in healthy sedentary subjects the effect of hand dominance on side-to-side difference in bone area and bone mass for upper and lower extremities. Dual-energy X-ray absorptiometry (DXA) measurements of both forearms and hips were performed on 193 right-handed and 20 left-handed subjects as determined by self-report. Scan acquisition and scan analyses were performed by one investigator, but all scan pairs were independently assessed for symmetry of positioning and movement artifacts by three investigators. Results show that DXA measurements between sides may be highly correlated regardless of the symmetry of the scan pair. However, asymmetric DXA scan pairs may have more than twice the side-to-side difference found in symmetric DXA scan pairs at the hip. Side-to-side differences between subregions were greater than the differences between measurements at the total radius, ulna, or hip. For symmetric pairs of DXA scans, the dominant forearm has significantly higher bone area and bone mineral content (BMC). Bone mineral density (BMD) was significantly higher only in the ulna of the dominant forearm. However, the nondominant forearm has higher values than dominant forearm in at least one DXA measurement in >24% of the subjects. There were no significant differences in any DXA measurements between hips, and higher DXA measurements did not occur significantly more frequently at the hip corresponding to the dominant hand. We conclude that healthy sedentary subjects tend to have proportionally higher bone area and BMC in the dominant forearm that results in similar BMD between dominant and nondominant forearms. This relationship does not appear to be applicable to measurements at the hip. In addition, there is a significant proportion of subjects with higher bone area and BMC in the nondominant extremities. Thus, in sedentary subjects, the consistency in the use of same extremity and the consistency in scan acquisition techniques and scan analyses is of greater importance than the selection of an extremity based on hand dominance in DXA studies.

Body Composition of Newborn Twins: Intrapair Differences

Objective: To measure body composition in newborn twins and to test the hypothesis that differences in body weights between twins are reflected proportionally by their differences in various components of body composition. Methods: 48 pairs of newborn twins delivered at a tertiary teaching hospital had dual energy x-ray absorptiometry (DXA) body composition measurement for bone mineral content (BMC), lean and fat mass (LM, FM). Data analyzed with regression and analysis of variance. Results: Body weight, BMC, LM and FM increased with increased gestational age (p < 0.001). The percent difference in BW between each twin pair was significantly correlated with percent difference in BMC, LM, and FM (p < 0.001). However, mean (± SD) percent difference in body weight (14.3 ± 10.0%) was significantly lower (p < 0.001) than FM (26.0 ± 15.0%) but was not significantly different from LM (13.4 ± 9.0%) or BMC (15.9 ± 11.6%). Conclusion: In newborn twins, body weight and body composition varies with gestational age. For any twin pair, a difference in body weight was correlated with but not proportional to differences in individual components of body composition.

VALIDATION OF ANTHROPOMETRY DERIVED BODY COMPOSITION (BC) WITH DUAL ENERGY X-RAY ABSORPTIOMETRY (DXA) IN NEONATES † 1393

VALIDATION OF ANTHROPOMETRY DERIVED BODY COMPOSITION (BC) WITH DUAL ENERGY X-RAY ABSORPTIOMETRY (DXA) IN NEONATES † 1393

Effect of Chronic Maternal Calcium (Ca) Supplementation on Fetal Bone Mineralization (FBM). † 1535

Pregnancy is a time of physiologic stress on Ca homeostasis but there has been no systematic study on the effect of maternal Ca intake on FBM. We tested the hypothesis that maternal Ca supplementation increases FBM as indicated by dual energy X-ray absorptiometry (DXA) measurements of the neonate. Two hundred eighty-nine women enrolled in a randomized trial of Ca supplementation during pregnancy were approached to participate in a study of FBM; 276 agreed. The women had been randomized to receive 2-g elemental Ca or placebo tablets daily from 13-21 wks gestation until delivery. At each prenatal visit compliance was determined by pill counts. The treatment grp received an average of 1284 mg supplemental Ca/d. All mothers were provided with the same prenatal vitamin supplement. There were no significant differences in maternal dietary Ca, protein and energy intake between grps based on the average of 24-hr recalls conducted at randomization and at 32-33 wks gestation. There was also no significant difference between grps in maternal body mass index and wt gain during pregnancy. Eight neonates were not studied because of 2 deaths, 5 technical problems with DXA and learly discharge. Twelve infants had delayed DXA studies beyond one week after birth because of illness. Of the remaining 256 infants (128/grp), DXA measurements were performed by the same operator at 1.75 (mean) ± 0.1 (SEM) d. Scan acquisition used Hologic 1000/W densitometer (Hologic Inc., Waltham, MA) and infant platform. Quality control scans using manufacturer supplied phantom showed a long term (>3 yrs) CV of<0.5%. Only scans without movement artifact were analyzed using software(v5.64 for total body and v4.57Q for spine) developed in conjunction with the manufacturer. General linear modeling showed that the mean total body bone mineral content (BMC) and lumbar spine BMC were significantly (p<0.05) higher in the treatment grp (13.4% and 14.6%, respectively) at the lowest quintile of maternal dietary Ca intake (mean 504 [treatment] vs 555 [placebo] mg/d). The effect of Ca supplementation on FBM was not significantly different at the highest quintile of dietary Ca intake. We conclude that FBM can be significantly improved by Ca supplementation at low maternal dietary Ca intake.

BODY COMPOSITION OF LARGE-FOR-GESTATIONAL AGE INFANTS. 1266

There are no reports on direct measurements of body composition in macrosomic infants. We hypothesize that large-for-gestational age (LGA) infants will have higher total body fat (TBF), lean body mass (LBM) and bone mineral content (BMC) as assessed by dual energy x-ray absorptiometry (DXA) when compared to appropriate birth weight for gestational age (AGA) infants. Thirty-seven LGA term infants (24B, 13W; 22M, 15F) with birth weights from 4000 g to 5040 g were compared with 37 gestational age-matched AGA infants(20B, 17W; 21M, 16F) with birth weights from 2700g to 3990g. Ten of the LGA infants were born to mothers with gestational (8) and class B (1) and C (1) diabetes. DXA scans were performed at 1.8±0.97 days after birth using Hologic QDR 1000/W densitometer with a pediatric platform. Scan analyses were performed with software version V5.64P. LGA infants had significantly(p<0.001) higher total amounts of mean (±SD) TBF (1008±288g vs 524±145g), LBM (3414±208g vs 2740±197g) and BMC(99.2±11.23g vs 66.6±8.95g). However, as a percent of body weight, LGA infants had significantly higher TBF (22±5.09% vs 15.6±3.37%) and lower LBM (75.8±5.12% vs 82.4±3.47%)(p<0.001, respectively) but similar levels of BMC when compared to AGA infants. Infants of diabetic mothers had similar but exaggerated changes in body composition, i.e., greater TBF and relatively lower LBM. We conclude that LGA infants have significantly different body composition from that of AGA infants, specifically there is disproportionately higher body fat and lower lean body mass, but there is proportionate increase in bone mineral content. These findings on changes of body composition in macrosomic infants may provide insight into the effect of in utero environment on fetal growth and improve postnatal management of such infants.