Body composition by dual-photon absorptiometry and dual-energy x-ray absorptiometry

Obesity and anthropometry in spina bifida: What is the best measure

OBJECTIVE

Diagnosis of obesity using traditional body mass index (BMI) using length may not be a reliable indicator of body composition in spina bifida (SB). We examine traditional and surrogate measures of adiposity in adults with SB, correlated with activity, metabolic disease, attitudes towards exercise and quality of life.

DESIGN

Adult subjects with SB underwent obesity classification using BMI by length and arm span, abdominal girth and percent trunk fat (TF) on dual energy X-ray absorptiometry (DXA). Quality of life measures, activity level and metabolic laboratory values were also reviewed.

RESULTS

Among eighteen subjects (6 male, 12 female), median age was 26.5 (range 19-37) years, with level of lesion 16.7% ≤L2, 61.1% L3-4, and 22.2% ≥L5, respectively. Median weight was 71.8 (IQR 62.4, 85.8) kg, similar between sexes (P = 0.66). With median length of 152.0 (IQR 141.8, 163.3) cm, median conventional BMI was 29.4 m/kg², with 7 (43.8%) subjects with BMI >30. Median BMI by arm span was 30.2 m/kg², abdominal girth of 105.5 cm, and TF 45.7%. More subjects were classified as obese using alternate measures, with 9 (56.3%) by arm span, 14 (82.4%) by abdominal girth and 15 (83.3%) by TF (P = 0.008). Reclassification of obesity from conventional BMI was significant when using TF (P = 0.03). No difference in quality of life measures, activity level and metabolic abnormalities was demonstrated between obese and non-obese subjects.

CONCLUSIONS

Conventional determination of obesity using BMI by length is an insensitive marker in adults with SB. Adults with SB are more often classified as obese using TF by DXA.

Body composition and resting energy expenditure in patients aged 11 to 21 years with spinal cord dysfunction compared to controls: comparisons and relationships among the groups

OBJECTIVES

To compare body composition in patients aged 11 to 21 years with spinal dysfunction due to spinal cord injury (SCI) and spina bifida (SB) vs. able-bodied control (CTRL) and able-bodied overweight (OW) groups and to examine the relationships between resting energy expenditure (REE) and total lean mass (TLM) in the SCI, SB, CTRL, and OW groups.

METHODS

Two hundred fifteen subjects, including 85 CTRL, 31 OW, 33 SCI, and 66 SB, were evaluated. Body composition was estimated by dual energy x-ray absorptiometry (DXA). Measurements included height, weight, total lean mass (TLM), fat tissue mass (FTM), body mass index (BMI), BMI percentile (BMI%tile), and % fat. Resting energy measurements were obtained in fasting subjects with an open-circuit indirect calorimeter.

RESULTS

There were gender differences in height, weight, BMI, TLM, fat mass, % fat, and REE. The REE in the SCI and SB groups was significantly different from that in the CTRL and OW groups, but no significant difference was found between the SCI and SB groups. The SB group had significantly higher REE/TLM ratios than did the other groups. The % fat was significantly higher in the SB and OW groups as compared to the CTRL and SCI groups. TLM was significantly higher in CTRL and OW groups as compared to SCI and SB groups, with the lowest TLM found in the SB group.

CONCLUSION

Patients aged 11 to 21 years with SB or SCI have significant lean tissue mass deficits by DXA as compared to able-bodied CTRL and OW groups, with the greatest deficits in total lean mass measured in SB. The absolute REE values were significantly reduced in both SCI and SB groups in association with their lean tissue deficits. Interestingly, REE/TLM ratios were remarkably constant in the CTRL, OW, and SCI groups but significantly elevated in the SB group. One would expect an even greater degree of adiposity in the SB group if their REE/TLM ratios were not elevated relative to those without congenital paralysis.

Genetic markers, bone mineral density, and serum osteocalcin levels

We evaluated five genetic markers for products that contribute to skeletal mineralization including the Sp1 polymorphism for type I collagen Ai (COLIA1), the vitamin D receptor (VDR) translation initiation site polymorphism, the promoter of the osteocalcin gene containing a C/T polymorphism, the estrogen receptor (ER) gene containing a TA repeat, and the polymorphic (AGC)n site in the androgen receptor. These markers were evaluated for their potential relationship with bone mineral density (BMD), measured by dual-energy X-ray densitometry, or its 3-year change. Additionally, potential associations of these genotypes and with baseline osteocalcin concentration or its 3-year change (assessed using radioimmunoassay) were evaluated. The study was conducted in 261 pre- and perimenopausal women of the Michigan Bone Health Study, a population-based longitudinal study of musculoskeletal characteristics and diseases. The polymorphic (AGC)n site in the androgen receptor showed a strong association with BMD of the femoral neck (FN) and lumbar spine and remained highly significant after adjusting for body mass index (BMI), oophorectomy/hysterectomy, oral contraceptive (OC) use and hormone replacement use (p < 0.001). The TA repeat at the 5' end of the ER gene was associated with total body calcium (p < 0.05) after adjusting for BMI, oophorectomy and hysterectomy, and OC use. The frequency of oophorectomy and hysterectomy within selected genotypes explained much of the statistically significant association of the ER genotypes with BMD of the FN and spine. There was no association of measures of BMD or bone turnover with the Sp1 polymorphism for COLIA1, the VDR translation initiation site polymorphism, or the C/T promoter polymorphism of the osteocalcin gene. These findings suggest that sex hormone genes may be important contributors to the variation in BMD among pre- and perimenopausal women.

Bone mineral density and its change in white women: estrogen and vitamin D receptor genotypes and their interaction

Low bone mineral density (BMD) is a major risk factor for development of osteoporosis; increasing evidence suggests that attainment and maintenance of peak bone mass as well as bone turnover and bone loss have strong genetic determinants. We examined the association of BMD levels and their change over a 3-year period, and polymorphisms of the estrogen receptor (ER), vitamin D receptor (VDR), type I collagen, osteonectin, osteopontin, and osteocalcin genes in pre- and perimenopausal women who were part of the Michigan Bone Health Study, a population-based longitudinal study of BMD. Body composition measurements, reproductive hormone profiles, bone-related serum protein measurements, and life-style characteristics were also available on each woman. Based on evaluation of women, ER genotypes (identified by PvuII [n = 253] and XbaI [n = 248]) were significantly predictive of both lumbar spine (p < 0.05) and total body BMD level, but not their change over the 3-year period examined. The VDR BsmI restriction fragment length polymorphism was not associated with baseline BMD, change in BMD over time, or any of the bone-related serum and body composition measurements in the 372 women in whom it was evaluated. Likewise, none of the other polymorphic markers was associated with BMD measurements. However, we identified a significant gene x gene interaction effect (p < 0.05) for the VDR locus and PvuII (p < 0.005) and XbaI (p < 0.05) polymorphisms, which impacted BMD levels. Women who had the (-/-) PvuII ER and bb VDR genotype combination had a very high average BMD, while individuals with the (-/-) PvuII ER and BB VDR genotype had significantly lower BMD levels. This contrast was not explained by differences in serum levels of osteocalcin, parathyroid hormone, 1,25-dihydroxyvitamin D, or 25-dihydroxyvitamin D. These data suggest that genetic variation at the ER locus, singly and in relation to the vitamin D receptor gene, influences attainment and maintenance of peak bone mass in younger women, which in turn may render some individuals more susceptible to osteoporosis than others.