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Biomedical subjects

M Peacock

Publications and source records attributed to M Peacock.

At least 55 records · Page 3Linked to original sources
PubMed1997

Calcium retention in relation to calcium intake and postmenarcheal age in adolescent females.

Achievement of maximal calcium retention during adolescence may influence the magnitude of peak bone mass and subsequently lower the risk of osteoporosis. Calcium retention is generally considered to reach a plateau at a certain calcium intake. To test this hypothesis, calcium balance was measured in 35 females with a mean (+/-SD) age of 12.7 +/- 1.2 y (range: 12-15 y) who consumed from 841 +/- 153 to 2173 +/- 149 mg Ca/d. Subjects ate a basal diet that included a fortified beverage containing different amounts of calcium citrate malate. Twenty-one subjects were studied at two dietary calcium intakes with use of a crossover design. Results from a previous study in 14 subjects who were studied at only one calcium intake were included in the data analysis. Calcium retention was modeled as a nonlinear function of calcium intake that included a parameter representing mean maximal retention. Mean maximal calcium retention was 473 mg/d (95% CI: 245, 701 mg Ca/d). At higher postmenarcheal ages, maximal calcium retention was lower but the intake required to achieve this was not affected. Calcium intake explained 79% and 6%, respectively, of the variation in fecal and urinary calcium excretion. Intake of 1200 mg Ca/d, the recommended dietary allowance for calcium published in 1989, resulted in a mean calcium retention that was 57% of the maximal value (95% CI: 25%, 89%). Intake of 1300 mg Ca/d was the smallest intake that allowed some adolescent females to achieve 100% of maximal calcium retention (95% CI: 26%, 100%). These data support the idea that calcium retention plateaus at a certain calcium intake although it continues to increase at intakes > 2 g/d.

Adolescent↗
PubMed1997

Differences in muscle endurance and recovery between fallers and nonfallers, and between young and older women.

BACKGROUND: Significant morbidity and mortality are associated with falls in older adults. We tested the hypothesis that older women with a history of falls demonstrate decreased muscle endurance and longer recovery times following fatiguing exercise. METHODS: We evaluated dynamic endurance and recoverability of the quadriceps femoris of 29 young women (YW) (M age = 21.7), 26 older women with a history of falls (FA) (M age = 73.3), and 27 older women with no history of falls (NF) (M age = 71.2) using an isokinetic dynamometer. Subjects performed repeated maximal concentric knee extensions until the force output of two consecutive repetitions fell below 50% of their maximal voluntary contraction (MVC). Recovery was defined as the time required for the return of force output > or = 80% MVC for 2 consecutive repetitions, within a set consisting of 3 maximal contractions. One minute rest was allowed between sets. We collected electromyographic (EMG) data from the quadriceps during all testing to evaluate spectral shifts. RESULTS: ANOVA with a post-hoc Bonferroni-Dunn test revealed time to fatigue was significantly faster in FA than YW (p < .02) and in FA than NF (p < .05), but not different between YW and NF. Time to recovery was significantly slower in FA than YW (p = .01), but not different between YW and NF, or between FA and NF, EMG median frequency power shift (from the beginning to the end of the test) was significantly less in FA (p < .001) than either YW (p < .002) or NF (p < .05). CONCLUSIONS: Older women with a history of falls demonstrate decreased muscular endurance compared to YW and NF, and increased time to recover from fatiguing exercise when compared to young women.

Accidental Falls↗
PubMed1997

Magnesium kinetics in adolescent girls determined using stable isotopes: effects of high and low calcium intake.

Magnesium kinetics were measured in five adolescent girls who were participating in a calcium balance study. Two calcium levels were fed in a randomized crossover design. After an acclimation period, 26Mg was consumed orally and 25Mg was given intravenously, and then blood, urine, and feces were collected for 14 days. Total magnesium and percent enrichment were determined, and data were fitted to a eight-compartment model. There was no significant difference between high and low calcium intakes for any of the parameters examined. Mean values for control (800 mg/day) and high (1,800 mg/day) calcium intake were as follows: Mg intake, 305 +/- 30 and 286 +/- 9 mg/day; absorption (percent), 44 +/- 7 and 39 +/- 9; absorption (mg/day), 134 +/- 35 and 110 +/- 28; urinary excretion, 96 +/- 22 and 101 +/- 31 mg/day; fecal excretion, 175 +/- 32 and 200 +/- 11 mg/day; and magnesium balance, 13 +/- 35 and -34 +/- 48 mg/day, respectively. In conclusion, high calcium intake did not alter magnesium kinetics or balance in adolescent girls.

Absorption↗
PubMed1997

Quantification of biochemical markers of bone turnover by kinetic measures of bone formation and resorption in young healthy females.

The quantification of biochemical markers of bone formation and resorption with kinetic measures of bone turnover is an essential step in their validation. Some biochemical markers have been validated by quantification against formation and resorption rates measured by calcium kinetics in adults with bone disease. However, none has been validated in healthy individuals who are undergoing skeletal growth and bone consolidation. Therefore, we have measured biochemical markers of bone formation (serum osteocalcin [OC], bone-specific alkaline phosphatase [BAP], and total alkaline phosphatase [ALP]) and resorption (serum tartrate resistant acid phosphatase [TRAP], urinary cross-linked N teleopeptides of type I collagen/creatinine [NTx/Cr], and hydroxyproline/creatinine [OHP/Cr]) in healthy females aged 11-32 years (n = 31) after an overnight fast to determine their relationship with bone formation (Vo+) and bone resorption (Vo-) as measured by calcium kinetics and balance. All biochemical markers were highly intercorrelated (r > 0.6, p < 0.001) as were Vo+ and Vo- (r = 0.91, p < 0.001). Highly significant correlations were present between bone formation measured by calcium kinetics (Vo+) and serum levels of bone biochemical markers (OC, r = 0.82, p = 0.001; ALP, r = 0.92, p = 0.001; and BAP, r = 0.90, p = 0.001) and between bone resorption measured by calcium kinetics (Vo-) and fasting serum levels and urine creatinine ratios of biochemical markers (TRAP, r = 0.77, p < 0.001; OHP/Cr, r = 0.79, p < 0.001; and NTx/Cr, r = 0.70, p < 0.001). Thus, biochemical markers of bone formation and resorption can be used to predict calcium kinetic rates during skeletal growth and the early years of formation of peak bone mass, ages at which strategies to build peak bone mass are important. Biochemical markers of formation and resorption are equally useful in predicting either the bone formation rate or the resorption rate.

Acid Phosphatase↗
PubMed1997

Reduced rates of skeletal remodeling are associated with increased bone mineral density during the development of peak skeletal mass.

Two related studies were conducted to assess the associations between markers of skeletal modeling and remodeling in healthy children. Members of monozygotic twin pairs, aged 6-14, enrolled in a clinical trial of calcium supplementation, were studied at the end of the period of supplementation and for 3 years thereafter. Supplemented children had significantly higher rates of gain in bone mineral density (BMD) (+3% on average) during the period of supplementation accompanied by significantly lower concentrations of serum osteocalcin (OC, -15%). During postsupplement follow-up, both differences in BMD and OC disappeared. Black females, age matched to the baseline ages of the white children, had significantly lower serum concentrations of both OC and tartrate-resistant acid phosphatase (TRAP) at all ages and higher BMDs. When stratified on serum TRAP concentrations, regardless of race, children with lower concentrations had significantly higher BMDs, and no racial differences were apparent. In regression models accounting for 70-80% of the variability in BMD in children, body size and TRAP, but not race, remained significantly associated with BMD. The skeletal advantages seen with calcium supplementation and black race appear to be associated with reduced rates of skeletal turnover. Given that markers of turnover during growth reflect both skeletal modeling and remodeling, and there is no apparent advantage to reduced skeletal modeling, it seems probable that reduced remodeling is the factor that accounts for the increases in bone mass.

Acid Phosphatase↗
PubMed1996

Sex steroids, bone mass, and bone loss. A prospective study of pre-, peri-, and postmenopausal women.

Although bone loss around the time of menopause is driven by estrogen deficiency, the roles of estrogens and androgens in the preservation of skeletal mass at other stages of life are less well understood. To address this issue we studied 231 women between the ages of 32 and 77 with multiple measurements of sex steroids and bone mass over a period of 2-8 yr. In all women bone mass was negatively associated with concentrations of sex-hormone binding globulin, and positively associated with weight. Bone loss occurred from all skeletal sites in peri- and postmenopausal women, but premenopausal women lost bone only from the hip (-0.3%/yr) and had positive rates of change in the radius and spine. Bone loss was significantly associated with lower androgen concentrations in premenopausal women, and with lower estrogens and androgens in peri- and postmenopausal women. Sex steroids are important for the maintenance of skeletal integrity before menopause, and for as long as 20-25 yr afterwards.

Adult↗
PubMed1996

The genetics of proximal femur geometry, distribution of bone mass and bone mineral density.

To estimate genetic effects on femoral neck geometry and the distribution of bone mineral within the proximal femur a cross-sectional twin analysis was carried out at a university hospital that compared correlations in these traits in pairs of mono- and dizygotic female twins. Monozygotic (MZ, n = 51 pairs, age 49.1 +/- 9.3 years) and dizygotic (DZ, n = 26 pairs, age 45.7 +/- 11.3 years) twins were randomly selected from a larger sample of twins previously studied. Measurements of bone mineral density (BMD), femoral neck angles and length, cross-sectional area and moment of interia, the center of mass of the narrowest cross-section of the femoral neck, and BMDs of regions within the femoral neck were made. A summary index of the resistance of the femoral neck to forces experienced in a fall with impact on the greater trochanter (Fall Index, FI) was calculated. MZ pair intraclass correlations (rMZ) were significantly (p < 0.05) different from zero for all bone mass and femoral geometry variables (0.35 < rMZ < 0.82). DZ pair correlations (rDZ) were lower than rMZ for all variables (0.04 < rDZ < 0.52) except femoral neck length (rDZ = 0.38, rMZ = 0.36). After adjustment for BMD of the femoral neck, rMZ was significantly greater than rDZ, yielding high heritability estimates for regional BMDs (0.72 < H2 < 0.78), the center of mass of the femoral neck (H2 = 0.70, -0.04 to 1.43 95% CI) and the resistance of the femoral neck to forces experienced in a fall (FI, H2 = 0.94, 0.06 to 1.85 95% CI), but not for femoral neck length. Adjustments for age did not alter these findings. It is concluded that there are significant familial influences on the distribution of femoral bone mass and on the calculated structural strength of the proximal femur, but not on femoral neck length. If the assumptions of the twin model are correct, this is evidence for genetic factors influencing these traits.

Absorptiometry, Photon↗
PubMed1996

A comparison of the urinary excretion of bone resorptive products in white and black children.

Bone density is greater in blacks than in whites regardless of age. In adults, bone formation was shown previously to be much lower in blacks than in whites. A lower bone turnover in adult blacks may preserve a high bone density acquired earlier in life. Whether there is a difference in bone turnover in blacks and whites early in life is not known. Bone resorption is known to parallel bone formation, and thus in the present study we looked for racial differences in bone turnover in children by measuring the nocturnal urinary excretion of three markers of bone resorption: hydroxyproline and the pyridinium cross-links, pyridinoline and deoxypyridinoline. Sixty-four black and 145 white children ages 6 through 15 years were studied. We found excretion of hydroxyproline to be similar in whites and blacks. Urinary excretion of the cross-links was about 10% to 15% lower in blacks, but only the excretion of pyridinoline in boys was significantly lower in blacks (p = 0.031). Overnight urinary calcium excretion was about 30% lower in blacks than in whites (p = 0.0016 for boys and p = 0.008 for girls), as has been reported previously by others. In summary, the excretion rates of bone resorptive products in white and black children were similar, suggesting nearly equal bone turnover in the two racial groups, a finding that contrasts with observations made previously in adults.

Adolescent↗
PubMed1996

Calcium absorption from apple and orange juice fortified with calcium citrate malate (CCM).

OBJECTIVE: Determine calcium (Ca) absorption from Ca fortified orange and apple juice. METHODS: Absorbability was assessed by measuring 45Ca absorption in healthy women (mean age 57 years, n = 57/group) and whole body 47Ca retention in adult female beagle dogs (n = 6/group) and young adult male rats (n = 6/group). Women received 6.24 mmol (250 mg) Ca as calcium citrate malate fortified orange juice (CCM-OJ) or apple juice (CCM-AJ). Dogs received 3.12 mmol (125 mg) Ca as CCM-OJ or CCM-AJ. Rats were administered 0.15 mmol (6 mg) Ca as either milk, CCM-OJ, or CCM-AJ. Additional 47Ca whole body retention experiments in rats measured the effects of differences in the carbohydrate and organic acid contents of the juices on Ca absorption. RESULTS: Mean +/- SEM percent Ca fractional absorption was greater (p < 0.003) in women who consumed CCM-AJ (42 +/- 2%) than those who consumed CCM-OJ (36 +/- 1%). Ca retention in dogs was 15 +/- 1% for CCM-OJ and 29 +/- 2% for CCM-AJ (p < 0.001). Ca retention was significantly different (p < 0.05) in rats administered milk (42 +/- 2%), CCM-OJ (52 +/- 2%), or CCM-AJ (61 +/- 2%). By manipulating the carbohydrate and organic acid concentrations of test solutions to mimic the composition of Ca fortified juices, we found that the greater fructose and lower organic acid content of apple juice accounted for its greater Ca absorbability. CONCLUSIONS: CCM fortified versions of orange and apple juice have high Ca absorbability and are potentially important vehicles for increasing dietary Ca intake. The greater Ca absorption from CCM-AJ compared with CCM-OJ is accounted for by differences in the carbohydrate and organic acid content of the juices. These data suggest that by modifying common beverage ingredients, products with even greater Ca absorbability could be formulated.

Absorption↗
PubMed1996

Calcium retention estimated from indicators of skeletal status in adolescent girls and young women.

To determine clinically useful predictors of calcium retention during postpubertal growth, calcium balance, bio-chemical markers of bone turnover, and anthropometric variables were determined in 14 girls aged 11-14 y and in 11 young women aged 19-30 y. Subjects participated in a 3-wk calcium-balance study with a calcium intake of 1332 mg/d. Biochemical markers of bone turnover (serum osteocalcin, total alkaline phosphatase, bone alkaline phosphatase, tartrate-resistant acid phosphatase, and urinary cross-linked N-teleopeptides of type I collagen and hydroxyproline as the creatinine ratios) were measured in fasting samples. Total-body bone mineral density and total-body calcium content were significantly higher in adults than in adolescents (1.17 compared with 1.05 g/cm2 and 1019 compared with 791 g, respectively). At the observed retention of 326 mg/d, adolescents would require 2 y to reach the total bone calcium of the young adults. All biomarkers of bone turnover were strikingly higher in adolescents than in adults and were strongly correlated with calcium retention. A multiple-regression model using a biochemical marker of bone turnover (serum osteocalcin) and postmenarcheal age (a measure of sexual maturation) described 75% of the variability in calcium retention.

Adolescent↗
PubMed1996

Differences in calcium kinetics between adolescent girls and young women.

Rapid bone accretion occurs throughout childhood but peaks during adolescence. The achievement of optimal peak bone mass, which can protect against osteoporosis later in life, is greatly dependent on rates of bone accretion. To identify differences in calcium metabolism during rapid vs. slower bone accretion, calcium kinetics were compared in 14 healthy girls aged 11-14 yr and 11 women aged 19-31 yr. Calcium kinetics were measured while subjects were undergoing a calcium balance study in a camp simulating a free-living environment. After 7 days on a diet containing 1,330 mg Ca/day, two stable isotopes were administered (44Ca orally and 42Ca intravenously), and blood samples and all urine and feces were collected for 14 days. Samples were analyzed for total calcium by atomic absorption spectrophotometry and for enrichment of 42Ca and 44Ca by fast atom bombardment mass spectrometry. Data from serum, urine, and feces were analyzed using the Simulation, Analysis and Modeling (SAAM) software. Data were fitted by a three-compartment model; the first pool was the same size in girls and women (1.6 g) but the second and third pools were larger in girls (2.85 vs. 1.66 g and 12 vs. 5 g). Compared with the women, girls absorbed more calcium from the diet (38 vs. 22% or 494 vs. 283 mg/day), excreted less calcium in urine (100 vs. 203 mg/day), deposited more calcium in bone (1,459 vs. 501 mg/day), and resorbed more calcium from the skeleton (1,177 vs. 542 mg/day), whereas endogenous calcium excretion did not differ between girls and women (112 vs. 121 mg/day). Girls retained more calcium than women (282 vs. -41 mg/day) through increased absorption, lower urine excretion, and higher bone turnover.

Absorption↗
PubMed1995

Peak bone mass in young women.

Increasing peak bone mineral density (BMD) or content (BMC) in young women may help to reduce the incidence of osteoporosis. Identifying the age when peak bone content or density is attained is essential to develop strategies aimed at optimizing peak BMD and BMC. Total body bone mineral density (TBBMD) and content (TBBMC) were measured by a dual X-ray absorptiometer in healthy females (n = 247, aged 11-32 years). TBBMD and TBBMC were modeled separately as a nonlinear function of age. By age 22.1 +/- 2.5 years, 99% of peak BMD is attained, and by age 26.2 +/- 3.7 years, 99% of peak BMC is attained. Nonlinear relationships between weight and TBBMD or TBBMC were also modeled. In this model, the influence of several parameters, including age, weight, and height, on BMC and BMD were simultaneously assessed. A model with age and weight described the best fit for TBBMD, whereas age, weight, and height described the best fit for total body TBBMC.

Absorptiometry, Photon↗
PubMed1995

Calcaneal ultrasonic measurements discriminate hip fracture independently of bone mass.

We studied 336 elderly white women, of whom 22 had previously suffered a hip fracture and 22 had previously suffered a vertebral fracture. All subjects were 60 years old or older with a mean age of 73:7 years. Measurements of ultrasonic transmission velocity (UTV), broad-band ultrasonic attenuation (BUA) and stiffness (STF) were made at the os calcis using a Lunar Achilles ultrasound device. Measurements of lumbar spine bone mineral density (L2-4 BMD) and femoral neck BMD were made using dual-energy X-ray absorptiometry. The fracture groups were significantly older and had more years since menopause than the control groups. Logistic regression showed that measurements of UTV, STF and BUA discriminated between fracture and non-fracture subjects for both the hip (p < 0.001) and spine (p < 0.05). Femoral neck BMD discriminated both hip and vertebral fractures from controls (p < 0.001 and p < 0.01, respectively). Spinal BMD discriminated between subjects with vertebral fractures and those without (p < 0.01), but not hip fractures (p = 0.64). For hip fracture, areas under receiver-operating characteristic (ROC) curves were 0.85 for UTV, 0.83 for STF, 0.79 for BUA, 0.78 for femoral neck BMD and 0.53 for spinal BMD. For vertebral fracture, areas under the ROC curve were 0.68 for UTV, 0.70 for STF, 0.66 for BUA, 0.66 for femoral neck BMD and 0.67 for spinal BMD.(ABSTRACT TRUNCATED AT 250 WORDS)

Aged↗
PubMed1995

Better discrimination of hip fracture using bone density, geometry and architecture.

Bone density predicts the risk of hip fracture. Because hip strength is determined by bone geometry and architecture as well as density, we tested which variables in geometry and architecture were independent discriminators of hip fracture and, if combined with density, improved the discrimination of fracture from non-fracture over bone density alone. The design was a case-control study. The subjects were Caucasian women over the age of 60 years who had sustained a hip fracture after the age of 58 years (n = 22), and controls matched for age and weight (n = 43) and unmatched controls (n = 317) with no history of hip fracture. Variables in density, geometry and architecture were obtained from dual-energy X-ray absorptiometry images and from radiographs of the upper end of the femur. In a univariate model, of the measures of bone mass, the best discriminator of hip fracture was bone mineral density of the neck of femur; of the geometric measurements, it was hip axis length; and of the measurements of bone architecture, it was Singh grade. In a multivariate model, these three variables were shown to be independent discriminators of hip fracture. When hip axis length was combined with bone mineral density, there was significant improvement in discrimination of hip fracture (p = 0.014), and when Singh grade was combined with hip axis length and bone mineral density there was a further significant improvement (p = 0.002).(ABSTRACT TRUNCATED AT 250 WORDS)

Absorptiometry, Photon↗
PubMed1995

Differences in calcium metabolism between adolescent and adult females.

A 3-wk metabolic study measured calcium balance in 14 white adolescent girls and 11 young adult women. Subjects were housed in a sorority to simulate a free-living environment. A 6-d menu cycle consisted of foods typically eaten by teenagers and averaged 1332 mg Ca/d. Adolescents had a significantly higher calcium balance of 326 +/- 107 mg/d (mean +/- SD) than adults, who averaged 73 +/- 104 mg/d (P < 0.001). No adult > age 21 y was in positive calcium balance. Adolescents had lower urinary calcium excretion values (P < 0.001), lower fecal calcium excretion (P < 0.01), and greater net absorption (P < 0.001) than adults. Calcium balance was negatively correlated with years postmenarche (r = -0.788, P = 0.0001) and height (r = -0.650, P = 0.001). Net calcium absorption was positively correlated with parathyroid hormone concentrations (r = 0.537, P = < 0.01). Thus, the growth demands of adolescents are met by more efficient net absorption and retention of calcium compared with young adults.

Adolescent↗
PubMed1995

Autosomal dominant, familial spastic paraplegia, type I: clinical and genetic analysis of a large North American family.

"Familial spastic paraplegia" (FSP) refers to clinically and genetically diverse syndromes characterized by insidiously progressive lower extremity spasticity. We evaluated 126 members of a large kindred, including 31 affected subjects, in which FSP was transmitted as a stereotyped, autosomal dominant disorder that showed complete genetic penetrance. Affected subjects developed insidiously progressive gait disturbance between ages 12 and thirty-five. Neurologic examination revealed hyperreflexia and spasticity in the lower extremities, weakness of hip flexion and ankle dorsiflexion, extensor plantar response, diminished vibratory sense in the feet, and pes cavus. Using genetic linkage analysis, we excluded the FSP1 locus on chromosome 14q11.2 as the disease locus in this family. We present the clinical and genetic features of FSP type I, including the age-adjusted risk of developing the disorder in this family.

Adolescent↗