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Biomedical subjects

M A Laskey

Publications and source records attributed to M A Laskey.

At least 19 recordsLinked to original sources
PubMed1999

Bone mineral changes during and after lactation.

OBJECTIVE: To assess bone mineral changes during and after lactation. METHODS: Fifty-nine breast-feeding women, 11 formula-feeding women, and 22 nonpregnant, nonlactating women had dual-energy x-ray absorptiometry measurements of the whole body, spine, hip, and forearm at 0.5 (baseline), 3, 6, and 12 months postpartum, with an additional measurement at 3 months after lactation for women who had breast-fed for more than 9 months. RESULTS: Lactation was associated with decreases in bone mineral at the whole body, spine, femoral neck, total hip, and radial wrist, which reversed as lactation declined and menstruation resumed. These changes were not seen in formula-feeding women. The magnitude and duration of the response were greater for women who breast-fed for a longer time. After lactation had stopped for at least 3 months, bone mineral, adjusted for bone area, had increased significantly above baseline at the whole body (+1.44%; 95% confidence interval [CI] +0.97%, +1.91%; P < .001), spine (+2.66%; 95% CI +1.60%, +3.72%; P < .001), and greater trochanter (+3.55%; 95% CI +2.53%, +4.57%; P < .001), was not different at the total hip and radial shaft, but was lower at the femoral neck (-2.07%; 95% CI -3.21%, -0.93%; P < .001) and radial wrist (-1.23%; 95% CI -1.99%, -0.47%; P < .01). Changes after lactation were largely independent of the duration of lactation or amenorrhea, and similar effects were observed in formula-feeding women. CONCLUSION: Lactation was associated with temporary decreases in bone mineral. After lactation, there were significant residual effects on bone mineral that were unrelated to the duration of lactation and may be related to having been pregnant. The long-term effect of lactation on the femoral neck requires further investigation.

Adult↗
PubMed1999

Anomalies in dual energy X-ray absorptiometry measurements of total-body bone mineral during weight change using Lunar, Hologic and Norland instruments.

A previous study showed that measurements of total-body bone mineral changes made with a Hologic QDR 1000W were unreliable when the subjects underwent weight change. The study has been extended to dual energy X-ray absorptiometry (DXA) apparatus from other manufacturers. Re-analysis of published results during weight loss using a Lunar DPX showed that they varied with the software used. Using the Extended mode, there was a 1% loss of bone mineral areal density (BMD), but no significant change in bone mineral content (BMC) or bone area (BA) following a weight loss of 16 kg, whereas the use of the Standard mode led to a larger fall of BMC and BMD. Similar findings arose from the consideration of two studies using Norland XR 26 HS absorptiometers. On the other hand, separation of two groups with similar weight changes from the population studied with a Hologic QDR 1000W confirmed that BMC changed directly with weight, but there was an inverse relationship for BMD, owing to an inappropriate change of BA. The use of Hologic Enhanced and Standard software modes led to significant differences in initial readings and measured changes. With each instrument there was a strong correlation between changes in BA and changes in BMC. When 6 kg of lard was wrapped around the limbs of volunteers or a semi-anthropomorphic phantom to simulate weight change, there were spurious increases of measured BMC and BA by about 5% with each instrument. There were no changes of BMD with Lunar, variable results with Norland, but decreases with Hologic. The results observed in vivo could be explained by the effects of fat changes, without there being any real change of bone mineral. Changes of BMD in the skeleton of the phantom were underestimated with all three brands. The anomaly observed with the Hologic QDR 1000W is less apparent with a Lunar DPX or a Norland XR 26, but there are sufficient uncertainties for all total-body measurements during weight change to be treated with suspicion.

Absorptiometry, Photon↗
PubMed1999

Comparison of adult and paediatric spine and whole body software for the Lunar dual energy X-ray absorptiometer.

Simple phantoms were devised to compare the performance of adult (software 3.64) and paediatric (software 3.8 g) spine and whole body software developed for the Lunar dual energy X-ray absorptiometer. Rectangular slabs of aluminium with high (1.18 g cm-2) and low (0.57 g cm-2) density were used to represent bone mineral. For spine measurements, the phantoms were scanned in water at depths of 5-20 cm. For whole body measurements, the phantoms were scanned with known amounts of oil and water to represent fat and lean tissue. This simulated tissue depths of 5.5-19.7 cm and body composition ranging from 14-29% fat. There were systematic differences in spine and whole body bone mineral content (BMC), bone area (BA) and bone mineral density (BMD) measurements and also between adult and paediatric software versions. The magnitude and direction of these differences were dependent on BMD of the phantom and tissue depth. Similar systematic differences were observed in vivo when volunteers were scanned using adult and paediatric software. Paediatric software enabled measurements to be made at low tissue depths. The weights of fat, lean and total soft tissue measured by the adult and paediatric whole body software were similar to the values calculated from the known composition of the phantom. Precision estimates for all softwares were excellent. In conclusion, paediatric software should improve bone mineral measurements of children but the discrepancies between adult and paediatric softwares may cause problems in longitudinal studies of skeletal growth and when compiling reference data from infancy through to adulthood.

Absorptiometry, Photon↗
PubMed1998

Bone changes after 3 mo of lactation: influence of calcium intake, breast-milk output, and vitamin D-receptor genotype.

Factors influencing the change in bone mineral after 3 mo of lactation were investigated in 47 breast-feeding mothers, 11 formula-feeding mothers, and 22 nonpregnant, nonlactating control subjects. At 6-8 wk postpartum, the breast-feeding group had a mean (+/-SD) calcium intake of 34.8+/-13.2 mmol/d and breast-milk volume, calcium concentration, and calcium output of 0.865+/-0.230 L/d, 7.41+/-1.25 mmol/L, and 6.41+/-2.00 mmol/d, respectively. There was no relation between calcium intake and any breast-milk variable. Dual-energy X-ray absorptiometry of the whole body, spine, hip, and forearm was performed at 0.5 and 3 mo. There were significant decreases in bone mineral content at the spine (3.96%; 95% CI: 4.86%, 3.06%), femoral neck (2.39%; 95% CI: 3.61%, 1.17%), total hip (1.51%; 95% CI: 2.45%, 0.60%), and whole body (0.86%; 95% CI: 1.29%, 0.43%) in breast-feeding mothers but not in formula-feeding mothers or nonpregnant, nonlactating women. These changes were not related to calcium intake, breast-milk calcium concentration, vitamin D-receptor genotype, postpartum weight change, or use of the progesterone-only contraceptive pill. After adjustment for bone area, breast-milk volume and height were identified as significant predictors at the spine, such that greater decreases were associated with taller mothers (P = 0.007) and those with greater breast-milk volume (P = 0.001). This finding suggests that the marked bone mineral changes observed in breast-feeding mothers represented a physiologic response to lactation that was independent of dietary calcium supply.

Absorptiometry, Photon↗
PubMed1997

Vitamin D status does not influence the breast-milk calcium concentration of lactating mothers accustomed to a low calcium intake.

Plasma 25-hydroxy-vitamin D and breast-milk calcium concentration were measured at 3 months of lactation in 60 Gambian mothers accustomed to a low calcium diet, of whom 30 were consuming a calcium supplement and 30 were receiving a placebo, and in 48 British mothers. The plasma 25-hydroxy-vitamin D concentration of the Gambian women was not affected by either calcium supplementation (supplemented, 64.4 +/- 2.5 nmol l(-1); placebo, 64.9 +/- 3.5 nmol l(-1); mean +/- SE) or season. The British average was lower (53.9 +/- 3.0 nmol l(-1), p = 0.004), owing to marked seasonal effects. The breast-milk calcium concentration was lower in The Gambia (supplemented, 5.38 +/- 0.13 mmol l(-1); placebo, 5.10 +/- 0.13 mmol l(-1); British, 6.93 +/- 0.15 mmol l(-1), p < 0.0001). There was no relationship between plasma 25-hydroxy-vitamin D and breast-milk calcium concentration in any group. There was no trend towards lower breast-milk calcium concentration in women with vitamin D status towards the bottom of the normal range or in British women during the winter. This study provides no support for the hypothesis that breast-milk calcium concentration is influenced by vitamin D status or that lactating women with a low calcium intake are at particular risk of vitamin D deficiency.

Adolescent↗
PubMed1996

Dual-energy X-ray absorptiometry and body composition.

This review describes the advantages and limitations of dual-energy absorptiometry (DXA), a technique that is widely used clinically to assess a patient's risk of osteoporosis and to monitor the effects of therapy. DXA is also increasingly used to measure body composition in terms of fat and fat-free mass. There are three commercial manufacturers of DXA instruments: Lunar, Hologic, and Norland. All systems generate X-rays at two different energies and make use of the differential attenuation of the X-ray beam at these two energies to calculate the bone mineral content and soft tissue composition in the scanned region. Most DXA instruments measure bone mineral in the clinically important sites of the spine, hip, and forearm. More specialized systems also perform whole-body scans and can be used to determine the bone and soft tissue composition of the whole body and subregions such as arms, legs, and trunk. The effective dose incurred during DXA scanning is very small, and, consequently, DXA is a simple and safe technique that can be used for children and the old and frail. Precision of all DXA measurements is excellent but varies with the region under investigation. Precision is best for young healthy subjects (coefficient of variation is about 1% for the spine and whole body bone measurements) but is less good for osteoporotic and obese subjects. The accuracy of DXA measurements, however, can be problematic. Marked systematic differences in bone and soft tissue values are found between the three commercial systems due to differences in calibration, bone edge detection, and other factors. In addition, differences in reference data provided by each manufacturer can lead to an individual appearing normal on one machine but at risk of osteoporosis on another. At present, DXA cannot be regarded as a "gold standard" for body composition. However, the continuing development of DXA and the introduction of new software is greatly improving the performance of this increasingly important technique.

Absorptiometry, Photon↗
PubMed1995

Effect of exercise training programme on bone mineral density in novice college rowers.

Exercise has important effects on skeletal mineralization. Changes in bone mineral density (BMD) and bone mineral content (BMC) as measured by dual energy X-ray absorptiometry were investigated in a group of 17 male novice college oarsmen over a 7-month period and were compared with eight age-matched controls. The rowing training programme consisted of approximately 8 h rowing, 1 h weight training, and 1 h running per week. After 7 months training the mean BMD of the lumbar spine (L1-L4) had increased significantly by 2.9% (P < 0.001) and the mean BMC had increased by 4.2% (P < 0.001). There was no significant change in the control group. Neither group showed a significant change in BMD or BMC in the femoral neck, greater trochanter or Ward's triangle. This study provides further evidence that exercise plays an important role in bone mineral formation.

Absorptiometry, Photon↗
PubMed1993

The calcium and phosphorus intakes of rural Gambian women during pregnancy and lactation.

The Ca and P intakes of 148 pregnant and lactating women in a rural village in The Gambia, West Africa, have been estimated by direct weighing of food on a total of 4188 d. The Ca and P contents of local foods were determined by analysis of raw ingredients, snack foods and prepared dishes. Information about the contribution of mineral-rich seasonings was obtained. Efforts were made to discover unusual sources of Ca that might not be perceived as food by subject or observer. The main contributors to daily Ca intake were shown to be leaves, fish, cereals, groundnuts and local salt. Cow's milk accounted for only 5% of Ca intake. Unusual sources of Ca were discovered, namely baobab (Adansonia digitata) fruit and selected earths, but these were consumed infrequently and their contributions to Ca intakes were small. Cereals and groundnuts were the main sources of P. Ca and P intakes (mg/d) were shown to average 404 (SD 110) and 887 (SD 219) respectively. Seasonal changes in the availability of leaves, cereals and groundnuts resulted in variations in Ca and P intakes. The rainy season was associated with increased Ca intakes (by 16%) but decreased P consumption (by 15%). No difference was observed in Ca intake between pregnant and lactating women but P intake in lactation was 11% higher than that in pregnancy during the post-harvest season. The implications of these low Ca intakes require investigation.

Adolescent↗
PubMed1992

Effect of diet-induced weight loss on total body bone mass.

1. Total body areal bone mineral density was measured by dual-energy X-ray absorptiometry in eight women before and 10 weeks after a very-low-calorie diet [405 kcal (1701 kJ)/day]. 2. The mean weight loss of 15.6 kg was accompanied by a statistically significant reduction in total body bone mineral density from 1.205 +/- 0.056 to 1.175 +/- 0.058 g/cm2 (mean +/- SD, P less than 0.005). 3. After cessation of the diet, weight gradually increased and by 10 months was similar to baseline values. Total body bone mineral density also increased after stopping the diet and mean values obtained 10 months after the diet did not differ significantly from initial values. Throughout the study total body bone mineral density values in all subjects were well within the range reported for normal subjects. 4. These data indicate that diet-induced weight loss is associated with rapid bone loss, subsequent weight gain being accompanied by increases in bone mass. Further studies are required to establish the clinical significance of these findings and, in particular, the skeletal distribution of bone loss.

Adult↗
PubMed1992

Four-component model for the assessment of body composition in humans: comparison with alternative methods, and evaluation of the density and hydration of fat-free mass.

1. Body composition was assessed in 28 healthy subjects (body mass index 20-28 kg/m2) by dual-energy X-ray absorptiometry, deuterium dilution, densitometry, 40K counting and four prediction methods (skinfold thickness, bioelectrical impedance, near-i.r. interactance and body mass index). Three- and four-component models of body composition were constructed from combinations of the reference methods. The results of all methods were compared. Precision was evaluated by analysis of propagation of errors. The density and hydration fraction of the fat-free mass were determined. 2. From the precision of the basic measurements, the propagation of errors for the estimation of fat (+/- SD) by the four-component model was found to be +/- 0.54 kg, by the three-component model, +/- 0.49 kg, by deuterium dilution, +/- 0.62 kg, and by densitometry, +/- 0.78 kg. Precision for the measurement of the density and hydration fraction of fat-free mass was +/- 0.0020 kg/l and +/- 0.0066, respectively. 3. The agreement between reference methods was generally better than between reference and alternative methods. Dual-energy X-ray absorptiometry predicted three- and four-component model body composition slightly less well than densitometry or deuterium dilution (both of which greatly influence these multi-component models). 4. The hydration fraction of fat-free mass was calculated to be 0.7382 +/- 0.0213 (range 0.6941-0.7837) and the density of fat-free mass was 1.1015 +/- 0.0073 kg/l (range 1.0795-1.1110 kg/l), with no significant difference between men and women for either. 5. The results suggest that the three- and four-component models are not compromised by errors arising from individual techniques.(ABSTRACT TRUNCATED AT 250 WORDS)

Absorptiometry, Photon↗
PubMed1992

Body composition and bone mass in post-menopausal women.

OBJECTIVE: We aimed to assess total body composition and to study the interrelationships between fat and lean tissue mass with total and regional bone mass in healthy British post-menopausal women. DESIGN AND PATIENTS: Total body composition and regional bone mass were measured in 97 healthy post-menopausal women recruited from the general community. The mean age was 57.9 years, range 49-65. MEASUREMENTS: Total body composition (fat, lean tissue and bone mineral) and regional bone density in the lumbar spine and femur were measured by dual energy X-ray absorptiometry on a Lunar DPX. RESULTS: Significant negative correlations with age were found for total body bone mineral density (r = -0.200, P = 0.049), and lumbar spine bone mineral density (r = -0.28, P = 0.006); the calculated rate of bone loss from these two sites was 0.33 and 0.7% per annum respectively. Fat tissue mass showed a positive correlation with age (r = 0.22, P = 0.03). High correlations were observed between total body and regional bone mineral density (r = 0.755-0.829, P < 0.001). After adjustment for age and lean mass, statistically significant correlations were seen between fat tissue mass and all bone mass measurements (P < 0.01-0.001), the strongest correlations being found for total body bone mineral content and density (r = 0.477 and 0.488 respectively). Lean tissue mass showed a strong correlation with total body bone mineral content (r = 0.580, P < 0.001), after adjustment for age and fat mass; it was less strongly correlated with other bone mass measurements than fat mass, showing only weak correlations with total body, trochanteric and lumbar spine bone mineral density (r = 0.228-0.246, P < 0.05). Age-adjusted body weight showed stronger correlations with total and regional bone mass than did either body mass index or height. CONCLUSIONS: Both fat and lean tissue mass are related to total and regional bone mass in post-menopausal women, the relationship being strongest for fat mass. Body weight shows stronger correlations with bone mass than either height or body mass index. In view of the direction and magnitude of changes in fat, lean tissue and bone mineral after the menopause, adiposity and muscularity are more likely to be determinants of peak bone mass than of the rate of post-menopausal bone loss.

Absorptiometry, Photon↗
PubMed1992

Assessment of the composition of major body regions by dual-energy X-ray absorptiometry (DEXA), with special reference to limb muscle mass.

Dual-energy X-ray absorptiometry (DEXA) has been used to assess and compare the composition of whole body and major body regions in 12 female (weight, 56.9 +/- 6.2 kg; BMI, 17-25 kg m-2) and 16 male (weight, 73.1 +/- 9.6 kg; BMI, 20-28 kg m-2) healthy subjects. Standard deviations (and % coefficients of variation) of the differences between repeated measurements of fat ranged from 0.11 kg (9.0%) for arms to 0.42 kg (3.0%) for whole body; for arm bone mineral, 0.01 kg (2.0%), and for fat-free soft tissue of the whole body, 0.42 kg (0.8%). Limb muscle mass was estimated using a new theoretical model of body composition, and the corresponding precision ranged from 0.15 kg (3.8%) to 0.27 kg (1.5%) for arms and total limb muscle mass, respectively. Proportions of each region consisting of fat were greater in females than in males (range, 20-31% vs. 16-18%), respectively, but the ratio of trunk to leg fat was lower (34:49% vs. 46:38%, respectively). Regional proportions of bone were similar between the sexes (all in the range 2.9-5.6%, for both females and males). Mean total limb muscle masses were 14.2 kg (arms, 2.8 kg; legs, 11.4 kg) for females and 22.2 kg (arms, 4.8 kg; legs, 17.4 kg) for males, which were 33.6% and 36.0% of fat-free mass, respectively. The correlation coefficients between limb muscle (DEXA) and other indices of muscle mass were: for DEXA vs. total body potassium, 0.90 (SEE 1.1 kg muscle mass) to 0.94 (1.6 kg); and for DEXA vs. anthropometry, 0.43 (1.2 kg) to 0.85 (1.3 kg). Those for limb volume (DEXA) vs. anthropometric volume, 0.91 (0.78 1) to 0.94 (1.91 1). It is concluded that DEXA enables the valid and reproducible estimation of fat, fat-free soft tissue, bone, and limb muscle mass.

Absorptiometry, Photon↗
PubMed1992

Comparison of the effect of different reference data on Lunar DPX and Hologic QDR-1000 dual-energy X-ray absorptiometers.

We have investigated whether the Lunar DPX (software 3.4) and Hologic QDR-1000 dual-energy X-ray absorptiometers have comparable normal reference databases for the spine and femur of white UK and USA subjects. After conversion for systematic differences in absolute bone density values between the two systems, the reference databases were very similar for the spine in young subjects, but there were clear differences in the femur databases of young females and males of all ages. These differences were confirmed by comparing the percent age-matched and young values determined by the two systems for subjects scanned on both systems. Thus the diagnosis and management of a patient could differ, depending on the system used for the bone density measurements.

Absorptiometry, Photon↗