Does Bone Loss Begin After Weight Loss Ends?
Does Bone Loss Begin After Weight Loss Ends?
Postmenopausal women who successfully completed a 6-month weight loss protocol in our laboratories were eligible for recruitment in this study. Participants were contacted approximately 2 years after their initial inclusion in a 6-month weight reduction program reported previously or that was part of small unpublished pilot studies from 2002 to 2008. To be eligible, postmenopausal women had to be healthy—without evidence of osteoporosis, metabolic bone disease, thyroid disorders, immune disease, myocardial infarction, or stroke in the past 6 months, or without kidney stones, diabetes, active cancers, or cancer therapy within the past 12 months. Participants were excluded if they changed their usual daily intake of supplemental calcium or multivitamin/mineral, started a new exercise program, or were taking medications known to influence bone metabolism, including hormone therapy. These studies were approved by the Rutgers University Institutional Review Board. All participants signed an informed consent form.
Participants were measured at three time points: baseline (time 0), 6 months of weight reduction (0.5 y), and final (2 y). During the weight loss period (0-0.5 y), participants underwent 6 months of weight loss interventions in our laboratories. In this protocol, participants were counseled—once weekly for the first 2 months and then twice monthly thereafter—by a registered dietitian to reduce their usual intake by 500 to 600 kcal/day while maintaining usual physical activity levels, as described previously. During the 6-month intervention, volunteers were given a multivitamin containing 400 IU of vitamin D3, and total calcium intake was at least 1,000 mg/day in all women. Upon completion of the intervention, all participants were counseled to consume approximately 1.2 g of Ca and 400 IU of vitamin D daily through diet and supplementation. After weight loss, there was a nointervention period (0.5-2.0 y), and participants were categorized according to weight change for this final measurement. Women who maintained their weight were recruited and agematched to a cohort of women who did not meet these criteria and regained their body weight (weight loss regainer [WL-R]) in a case-control design. For eligibility in the weight loss maintainer (WL-M) group, weight regain needed to be less than 25%. The WL-R group was composed of those who regained more than this amount.
Weight and height were measured to the nearest 0.25 kg and 0.25 cm, respectively, at baseline, after weight loss (0.5 y), and at the 2-year final measurement with a balance beam scale and a stadiometer, respectively (Detecto, Webb City, MO). BMD was measured at the femoral neck, trochanter, spine, total body, 1/3 radius, and ultradistal (UD) radius by dual-energy x-ray absorptiometry (DXA; GE Lunar, Madison, WI; coefficient of variation <1% for all sites). Scans were performed by using enCORE 2004 software (version 8.10.027; GE Lunar). Bone mineral content at each site was also measured. Fat-free soft tissue (FFST), total fat mass, trunk fat, and leg fat were measured by DXA using total body scans and the manufacturer’s standard cut lines for leg and trunk regions. Calcium intake was estimated using 3-day food records and analyzed using the US Department of Agriculture database (Food Works Software 10.1; Food Works, Long Valley, NJ).
Fasting morning blood samples were collected from the entire population at baseline and from a subset (n = 22) after 2 years. The bone formation marker osteocalcin (BTI, Stoughton, MA; coefficient of variation <9%) was measured by radioimmunoassay (RIA). Serum N-telopeptide of type I collagen was measured by enzyme-linked immunosorbent assay (Osteomark, Princeton, NJ; coefficient of variation <4.6%). Intact parathyroid hormone (PTH), 25-hydroxyvitamin D (25(OH)D), and estradiol were analyzed by RIA. The coefficient of variation was less than 6.8% for PTH (DSL, Webster, TX; Scantibodies, Santee, CA), less than 12.5% for 25(OH)D (DiaSorin, Stillwater, MN), and less than 12.2% for estradiol (DSL, Webster, TX). Our laboratory participates in a vitamin D external quality assessment scheme (DEQAS) to monitor the performance of the RIA used for 25(OH)D assessment.
Changes in body composition, hormones, and bone markers at the three time points (baseline, 0.5 y, and 2 y) between the groups (WL-R and WL-M) were analyzed by a two-factor repeated-measures analysis of variance (ANOVA). If the F test was significant, post hoc analysis was performed using Tukey’s pairwise multiple comparison. Changes in bone markers between the groups from baseline to final measurement were analyzed using one-way ANOVA. Annual BMD loss was determined at each site by dividing the percent change in BMD by the number of months during the entire study period for each individual. Multiple regression analysis was used to assess how the change in independent variables (age, leg fat, trunk fat, and FFST) across time influenced the change in BMD at each site. To determine whether weight loss and weight regain will have a similar effect on BMD, we performed a power analysis with α set to 0.05 and with β set to 0.90 using trochanter BMD change during weight loss or maintenance. This analysis indicated that 15 participants per group would be necessary to avoid a type II error, and we included at least five additional participants per group to account for two possible baseline covariates. Values are expressed as mean (SD), except in figures, which include SEM to improve visual clarity. Analysis was performed with SAS statistical software version 9.2 (SAS Institute Inc, Cary, NC).
Methods
Participants
Postmenopausal women who successfully completed a 6-month weight loss protocol in our laboratories were eligible for recruitment in this study. Participants were contacted approximately 2 years after their initial inclusion in a 6-month weight reduction program reported previously or that was part of small unpublished pilot studies from 2002 to 2008. To be eligible, postmenopausal women had to be healthy—without evidence of osteoporosis, metabolic bone disease, thyroid disorders, immune disease, myocardial infarction, or stroke in the past 6 months, or without kidney stones, diabetes, active cancers, or cancer therapy within the past 12 months. Participants were excluded if they changed their usual daily intake of supplemental calcium or multivitamin/mineral, started a new exercise program, or were taking medications known to influence bone metabolism, including hormone therapy. These studies were approved by the Rutgers University Institutional Review Board. All participants signed an informed consent form.
Protocol
Participants were measured at three time points: baseline (time 0), 6 months of weight reduction (0.5 y), and final (2 y). During the weight loss period (0-0.5 y), participants underwent 6 months of weight loss interventions in our laboratories. In this protocol, participants were counseled—once weekly for the first 2 months and then twice monthly thereafter—by a registered dietitian to reduce their usual intake by 500 to 600 kcal/day while maintaining usual physical activity levels, as described previously. During the 6-month intervention, volunteers were given a multivitamin containing 400 IU of vitamin D3, and total calcium intake was at least 1,000 mg/day in all women. Upon completion of the intervention, all participants were counseled to consume approximately 1.2 g of Ca and 400 IU of vitamin D daily through diet and supplementation. After weight loss, there was a nointervention period (0.5-2.0 y), and participants were categorized according to weight change for this final measurement. Women who maintained their weight were recruited and agematched to a cohort of women who did not meet these criteria and regained their body weight (weight loss regainer [WL-R]) in a case-control design. For eligibility in the weight loss maintainer (WL-M) group, weight regain needed to be less than 25%. The WL-R group was composed of those who regained more than this amount.
Bone and Body Composition Measurements and Serum Markers
Weight and height were measured to the nearest 0.25 kg and 0.25 cm, respectively, at baseline, after weight loss (0.5 y), and at the 2-year final measurement with a balance beam scale and a stadiometer, respectively (Detecto, Webb City, MO). BMD was measured at the femoral neck, trochanter, spine, total body, 1/3 radius, and ultradistal (UD) radius by dual-energy x-ray absorptiometry (DXA; GE Lunar, Madison, WI; coefficient of variation <1% for all sites). Scans were performed by using enCORE 2004 software (version 8.10.027; GE Lunar). Bone mineral content at each site was also measured. Fat-free soft tissue (FFST), total fat mass, trunk fat, and leg fat were measured by DXA using total body scans and the manufacturer’s standard cut lines for leg and trunk regions. Calcium intake was estimated using 3-day food records and analyzed using the US Department of Agriculture database (Food Works Software 10.1; Food Works, Long Valley, NJ).
Fasting morning blood samples were collected from the entire population at baseline and from a subset (n = 22) after 2 years. The bone formation marker osteocalcin (BTI, Stoughton, MA; coefficient of variation <9%) was measured by radioimmunoassay (RIA). Serum N-telopeptide of type I collagen was measured by enzyme-linked immunosorbent assay (Osteomark, Princeton, NJ; coefficient of variation <4.6%). Intact parathyroid hormone (PTH), 25-hydroxyvitamin D (25(OH)D), and estradiol were analyzed by RIA. The coefficient of variation was less than 6.8% for PTH (DSL, Webster, TX; Scantibodies, Santee, CA), less than 12.5% for 25(OH)D (DiaSorin, Stillwater, MN), and less than 12.2% for estradiol (DSL, Webster, TX). Our laboratory participates in a vitamin D external quality assessment scheme (DEQAS) to monitor the performance of the RIA used for 25(OH)D assessment.
Statistical Analysis
Changes in body composition, hormones, and bone markers at the three time points (baseline, 0.5 y, and 2 y) between the groups (WL-R and WL-M) were analyzed by a two-factor repeated-measures analysis of variance (ANOVA). If the F test was significant, post hoc analysis was performed using Tukey’s pairwise multiple comparison. Changes in bone markers between the groups from baseline to final measurement were analyzed using one-way ANOVA. Annual BMD loss was determined at each site by dividing the percent change in BMD by the number of months during the entire study period for each individual. Multiple regression analysis was used to assess how the change in independent variables (age, leg fat, trunk fat, and FFST) across time influenced the change in BMD at each site. To determine whether weight loss and weight regain will have a similar effect on BMD, we performed a power analysis with α set to 0.05 and with β set to 0.90 using trochanter BMD change during weight loss or maintenance. This analysis indicated that 15 participants per group would be necessary to avoid a type II error, and we included at least five additional participants per group to account for two possible baseline covariates. Values are expressed as mean (SD), except in figures, which include SEM to improve visual clarity. Analysis was performed with SAS statistical software version 9.2 (SAS Institute Inc, Cary, NC).