Sarcopenia and osteoporosis represent a growing public health problem. We studied the potential benefit of whole-body vibration (WBV) training given a conventional or a high dose of daily vitamin D supplementation in improving strength, muscle mass, and bone density in postmenopausal women. In a 2 × 2 factorial-design trial, 113 institutionalized elderly females aged over 70 years (mean age 79.6 years) were randomly assigned either to a WBV or a no-training group, receiving either a conventional dose (880 IU/day) or a high dose (1600 IU/day) of vitamin D3. The primary aim was to determine the effects of 6 months of WBV and/or vitamin D supplementation on isometric and dynamic strength, leg muscle mass, and hip bone mineral density (BMD). Additionally, the increase in 25-hydroxyvitamin D [25(OH)D] levels between conventional and high-dose supplementation was compared. After 6 months of treatment, dynamic muscle strength, hip BMD, and vitamin D serum levels improved significantly in all groups, whereas isometric strength and muscle mass did not change. When compared with no training, the WBV program did not result in additional improvements. When compared with 880 IU, a high dose of 1600 IU of vitamin D did result in higher serum vitamin D levels but did not result in additional improvements. In institutionalized women older than 70 years, the WBV training protocol tested is not more efficient in enhancing muscle mass, strength, and hip BMD compared with vitamin D supplementation. A higher dose of 1600 IU of vitamin D does not provide additional musculoskeletal benefit in this population compared with conventional doses. © 2011 American Society for Bone and Mineral Research.
Increases in the proportion of elderly populations across the world have resulted in sarcopenia (the loss in skeletal muscle mass and muscle strength) and osteoporosis (low bone mass and structural deterioration of bone tissue) becoming increasingly important public health issues. Between the ages of 40 and 80 years, muscle mass decreases by 30% to 50%,1 with the decline in muscle mass leading to physical frailty, increased risk of falls, impaired mobility, and a possible contribution to several age-related chronic disorders (eg, osteoporosis, type 2 diabetes, insulin resistance, and arthritis).2 After 50 years of age, bone mineral density (BMD) decreases on average by 3% per year in postmenopausal women.3–5 A frequent result of a decrease in skeletal BMD is an increase in bone fragility and increased risk of fracture.
A significant proportion of the elderly population is vitamin D deficient owing to low dietary intake, reduced sunlight exposure, and impaired hydroxylation in the liver and kidneys.6 This deficiency is associated with reduced muscle strength, lower performance in functional tests, higher propensity for falls, and increased bone loss.7, 8
Sarcopenia and osteoporosis can be prevented or reversed in part with targeted interventions in elderly populations. Vitamin D (combined with calcium supplementation) enhances lower extremity function, increases BMD, and reduces fall and fracture risk in older individuals.9–13
In addition to the established role of vitamin D and calcium supplementation, load-bearing training, including whole-body vibration (WBV) training, may prevent or even partially reverse sarcopenia and osteoporosis in community-dwelling postmenopausal women.14–17 During WBV training, the individual stands on a platform that generates vertical sinusoidal vibrations. Mechanical stimuli transmitted to the body stimulate the primary endings of the muscle spindles, resulting in neuronal activation and muscle contractions comparable with the tonic vibration reflex.18, 19 Vibration-induced increase in muscle activity results in significant improvements in muscle strength and muscle mass following 6 and 12 months of WBV training, as shown in studies in community-dwelling individuals with a mean age of 64 and 67 years, respectively.15, 16 Additionally, the high-frequency loading of the skeleton leads to enhancements in BMD of the hip.14, 17 However, it remains unclear if more frail, institutionalized elderly people (those at highest risk of sarcopenia, osteoporosis, falls, and fractures) remain sensitive to the vibration stimuli. In short-term trials (<8 weeks), significant improvements in balance and mobility measures have been reported in the geriatric population20–22 but with no enhancement in muscle strength.21
This randomized, controlled trial investigated the effects of 6 months of WBV training and of vitamin D (880 or 1600 IU) supplementation on muscle strength, muscle mass, and BMD in institutionalized women older than 70 years of age. Our main objective was to determine whether, in institutionalized elderly women, WBV training provides additional musculoskeletal benefits compared with a control group who received similar calcium and vitamin D supplementations but who did not follow training regimens. Our second aim was to compare the effects of high-dose (1600 IU) and conventional-dose (880 IU) supplementation with vitamin D.
Study design and patients
The study was approved by the Human Ethics Committee of the Katholieke Universiteit Leuven according to the Declaration of Helsinki. All participants gave written informed consent.
Institutionalized women older than 70 years of age were recruited between August 2006 and December 2007 in nursing homes, service flats, and cloistered communities around Leuven, Belgium. Women were excluded if they had regularly participated in endurance and/or strength training in the two years preceding the start of the study, if they participated in exercise programs for more than 2 hours a week at the time of recruitment, or if they were on medication influencing BMD, including both calcium and vitamin D, any osteoporotic medication, and corticosteroid treatment. Women had to be capable of standing unaided and of understanding instructions related to exercises and measurements. Finally, specific contraindications were checked before participation in a WBV training program,15, 16 and all women were medically screened by a physician affiliated with the Katholieke Universiteit Leuven. After approval for participation in the study by the general physician, 113 women were stratified for BMD of the total body measured by dual-energy X-ray absorptiometry (DXA) and consequently randomly assigned by a person unrelated to the study (concealed allocation) to either a WBV training program group or a control group not participating in any exercise program using computer-generated random numbers. These participants were randomly assigned a conventional (880 IU/day) or a high (1600 IU/day) dose of vitamin D3. All women received daily calcium supplementation (1000 mg).
The WBV group trained three times a week for 6 months and performed static and dynamic exercises on a vibration platform (Power Plate, Badhoevedorp, The Netherlands) involving squat, deep squat, wide-stance squat, toe stance, and one-legged squats. Training load increased gradually over the 6-month period according to the overload principle and was adapted according to individual physical abilities (Table 1). The amplitude of the vibrations stayed at a low setting (<2.2g), and training sessions were for a maximum duration of 15 minutes, including warm-up and cool-down. Vibration platforms were set up in the nursing homes, service flats, and cloistered communities, and all training sessions were supervised by a professional fitness instructor. The women were asked to report any side effects.
Table 1. Training Characteristics of the Whole-Body Vibration Training Program
|Volume||Total duration of vibration in one session (min)||1||12|
|Longest duration of vibration loading without rest (s)||15||60|
|Intensity||Vibration frequency (Hz)||30||40|
|Vibration amplitude (g)||1.6||2.2|
|Rest period between exercises (s)||60||5|
The control group did not participate in a training program, and the women were asked not to change their lifestyle during the course of the project.
The degree of frailty was determined by the modified Physical Performance Test (PPT) consisting of nine tasks representing a variety of daily activities and scored on a 4-point scale.23
Ascertainment of outcome
Knee extensor muscle strength, muscle mass of the upper limb, hip BMD, and serum vitamin D levels were documented at baseline and after 6 months of training. Muscle strength was assessed by an isokinetic dynamometer (Biodex, Shirley, NY, USA) by an expert blinded against group allocation. Testing procedures have been described in detail elsewhere.15, 16 Knee-extension isometric strength and dynamic strength measurements were performed, and the highest torque (N · m) was recorded. The highest strength values out of two repeats were used for further analyses.
A multislice CT scan (Siemens Sensation 16, Washington, DC, USA) was used to measure muscle mass of the upper leg. Measurements were performed at the Katholieke University Hospital Leuven by an expert radiologist blinded against group allocation. The muscle tissue area was segmented using standard Hounsfield units (0 to 100) for skeletal muscle.24 Muscle mass expressed as the cumulative muscle volume (cm3) of three slices was used for further analysis.16
BMD of the right hip was assessed by DXA (Hologic Discovery A with software Version 12.3.3, Waltham, MA, USA) at the Katholieke University Hospital Leuven by an expert blinded against group allocation.14
For vitamin D status, fasting blood samples were collected from all women and stored at −70°C until levels of 25(OH)D (nmol/L) were determined using radioimmunoassay (RIA Kit, DiaSorin, Stillwater, MN, USA). Intra- and interassay coefficients of variation (CVs) for 25(OH)D were 11% and 9%, respectively. The detection limit of the RIA Kit was 3.7 nmol/L of 25(OH)D.
Based on previous results in community-dwelling elderly women,16 a priori analysis revealed that a sample of 20 women in the WBV group would provide adequate statistical power (0.80) to detect a clinically relevant increase in isometric muscle strength of 10% after 6 months of vibration training (α = 0.05). Since this was the first long-term WBV intervention trial in institutionalized elderly women, a high dropout rate was expected, and more women were included.
Statistical analyses were done according to intention to treat on SPSS Version 17.0 (SPSS, Inc, Chicago, IL, USA). Descriptive statistics were used first to document baseline comparability of the women in the four treatment groups. The main effect of the training program on muscle strength, muscle mass, and hip BMD and the main effect of the vitamin D medication were analyzed by general linear model (GLM) repeated measures using ANOVA while controlling for the other treatment strategy. Interaction between the WBV training program and the vitamin D medication was tested for.
Dropouts and training compliance
A total of 194 female elderly women volunteered to participate in this study (Fig. 1). One hundred and thirty-two women passed the medical screening. Nine women dropped out between the medical screening and the pretests for personal reasons (n = 7) or as a result of additional health (n = 2) problems. During pretesting, a further 10 women quit the study for personal reasons (n = 9) or as a result of health problems (n = 1) unrelated to the testing. The remaining 113 women were randomly assigned to one of the four groups in the 2 × 2 factorial-design trial.
Of these 113 women, 10 women dropped out during the study: 8 for medical reasons unrelated to the testing, 1 because she could not tolerate the vitamin D supplementation and refused to continue with the treatment, and 1 owing to an aggravating degree of confusion. Additionally, 2 women died before the end of the study, resulting in 111 women included in the intention to treat (ITT) analyses.
No significant differences in baseline characteristics were found between the four treatment groups (all p values > .05; Table 2). According to the modified PPT, 21.1% of the women were considered “not frail” (32–36 points), 62.4% were “mildly frail” (25–31 points), 15.6% were “moderately frail” (17–24 points), and 0.9% could no longer function independently within the community (<17 points).23
Table 2. Characteristics at Trial Entry; Mean (and SD) or Number of Women (and Percentage)
|Age (years)||80.3 (SD 5.3)||79.8 (SD 5.3)||78.7 (SD 5.6)||79.6 (SD 5.2)||0.725|
|Weight (kg)||66.9 (SD 8.1)||63.7 (SD 11.5)||67.5 (SD 15.1)||68.4 (SD 11.8)||0.496|
|Height (cm)||156.6 (SD 6.5)||155.3 (SD 6.1)||156.3 (SD 5.9)||157.7 (SD 7.3)||0.587|
|BMI (kg/m2)||27.5 (SD 2.7)||26.4 (SD 4.4)||27.5 (SD 5.5)||27.4 (SD 3.7)||0.722|
|Frailty score (0 to 36 points)||28.5 (SD 4.8)||27.7 (SD 3.6)||27.4 (SD 5.7)||28.4 (SD 4.5)||0.775|
|Frailty Class|| || || || || |
| Class 1||0||0||1/29 (3.5%)||0|| |
| Class 2||6/26 (23.1%)||3/26 (11.55%)||4/29 (13.8%)||4/28 (14.3%)|| |
| Class 3||13/26 (50.0%)||20/26 (76.9%)||18/29 (61.1%)||17/28 (60.7%)|| |
| Class 4||7/26 (26.9%)||3/26 (11.55%)||6/29 (20.7%)||7/28 (25.0%)|| |
|Isometric muscle strength (Nm)||87.5 (SD 21.1)||78.4 (SD 21.8)||86.9 (SD 25.5)||85.2 (SD 26.3)||0.468|
|Dynamic muscle strength (Nm)||69.6 (SD 22.5)||64.7 (SD 18.2)||69.0 (SD 20.7)||66.3 (SD 24.8)||0.815|
|Muscle mass (cm3)||69.6 (SD 11.3)||67.3 (SD 8.0)||70.5 (SD 12.3)||72.1 (SD 10.2)||0.379|
|Hip bone mineral density (g/cm2)||0.804 (SD 0.125)||0.758 (SD 0.130)||0.766 (SD 0.159)||0.790 (SD 0.135)||0.602|
|Serum vitamin D level (nmol/L)||56.5 (SD 40.2)||51.7 (SD 27.1)||53.6 (SD 32.5)||51.3 (SD 37.2)||0.950|
|Women with vitamin D level < 50 nmol/L||14/23 (60.9%)||14/27 (51.9%)||13/25 (52.0%)||17/27 (63.0%)|| |
No adverse side effects of the intervention were reported in the WBV training group, and training sessions were not experienced as a strenuous workout, resulting in a level of compliance of more than 90%. Only 5 women reported a lower compliance rate owing to personal or health problems not related to the study.
WBV training program
Table 3 shows the main effects for the whole-body vibration (WBV) training program. After 6 months of treatment, dynamic muscle strength, hip BMD, and vitamin D serum levels improved significantly over time, whereas isometric strength and muscle mass did not change from baseline. These findings over time were similar in the WBV training program group and the no-exercise program group. Overall, the WBV training program did not result in additional increase in muscle strength, muscle mass, hip BMD, and serum vitamin D levels when compared with a no-exercise program.
Table 3. Main Effects, Whole-Body Vibration (WBV) Training Program
|Isometric muscle strength (Nm)||+4.48% (1.72)||+0.62% (1.97)||.184||+3.86% (−1.32 to +9.05)||.182|
|Dynamic muscle strength (Nm)||+7.94% (2.42)||+6.44% (2.04)||< .001||+1.50% (−4.79 to +7.78)||.881|
|Muscle mass (cm3)||−0.26% (0.45)||−0.11% (0.41)||.450||−0.14% (−1.35 to +1.06)||.706|
|Hip bone mineral density (g/cm2)||+0.75% (0.29)||+0.88% (0.32)||< .001||−0.14% (−0.99 to +0.72)||.949|
|Serum vitamin D level (nmol/L)||+171.27% (28.90)||+177.84% (26.74)||<.001||−6.56% (−84.60 to +71.46)||.628|
Vitamin D supplementation
Table 4 shows the main effects of vitamin D supplementation. After 6 months of treatment, dynamic muscle strength, hip BMD, and vitamin D serum levels improved significantly over time, whereas isometric strength and muscle mass did not change from baseline. A high dose of 1600 IU of vitamin D resulted in a larger increase of serum vitamin D levels compared with a dose of 880 IU. This larger increase in serum vitamin D levels with 1600 IU did not result in any additional increase in muscle strength or hip BMD when compared with patients on a conventional dose of 880 IU.
Table 4. Main Effects, Vitamin D Medication
|Isometric muscle strength (Nm)||+3.49% (1.65)||+1.61% (2.05)||.186||+1.88% (−3.34 to +7.11)||.409|
|Dynamic muscle strength (Nm)||+8.05% (2.55)||+6.33% (1.88)||< .001||+1.16% (−2.44 to +4.76)||.526|
|Muscle mass (cm3)||−0.16% (0.51)||−0.21% (0.34)||.456||+0.42% (−3.59 to +4.42)||.985|
|Hip bone mineral density (g/cm2)||+0.78% (0.28)||+0.86% (0.33)||< .001||−0.08% (−0.93 to +0.78)||.887|
|Serum vitamin D level (nmol/L)||+185.56% (29.66)||+164.91% (26.09)||< .001||+20.64% (−57.41 to +98.7)||.041|
Interestingly, vitamin D supplementation at any dose resulted in a circulating vitamin D level higher than 50 nmol/L in all women at 6 months, except for the 1 woman who had not taken the supplements (Fig. 1).
Table 5 shows the change from baseline for the four separate treatment groups and the p values for interaction between the two interventions. There was no evidence for an interactive effect between the WBV training program and vitamin D medication for any outcome.
Table 5. Separate Group Results and Interaction Effects
|Isometric muscle strength (Nm)||+6.07% (2.14)||+3.01% (2.67)||+1.10% (2.44)||+0.11% (3.18)||.330|
|Dynamic muscle strength (Nm)||+11.41% (4.42)||+4.71% (2.13)||+4.94% (2.66)||+8.07% (3.17)||.600|
|Muscle mass (cm3)||−0.36% (0.72)||−0.16% (0.57)||+0.02% (0.72)||−0.25% (0.38)||.350|
|Hip bone mineral density (g/cm2)||+0.78% (0.39)||+0.71% (0.42)||+0.78% (0.39)||+0.99% (0.51)||.179|
|Serum vitamin D level (nmol/L)||+200.01% (46.89)||+146.80% (35.78)||+172.25% (37.91)||+183.02% (38.34)||.668|
This is the first randomized, controlled trial assessing the effects of 6 months of WBV training on muscle strength, muscle mass, and BMD in institutionalized, elderly women taking vitamin D and calcium supplementation. In these women, dynamic muscle strength and BMD of the hip increased significantly and similarly over time in groups treated with or without WBV. Our findings suggest that in institutionalized elderly women, the present WBV training program of 6 months does not provide any additional musculoskeletal benefit over vitamin D supplementation. Likewise, a high dose of vitamin D (1600 IU) inducing significantly higher levels of circulating vitamin D compared with the conventional dose (880 IU) was not superior in enhancing muscle mass, muscle strength, or hip BMD in this trial population.
As noted in other studies, elderly institutionalized patients are frequently vitamin D deficient, defined as vitamin D levels of less than 50 nmol/L,8, 25 and in this study, most of the patients (56.9%) had vitamin D levels below this level at baseline. Vitamin D supplementation at the doses used in this trial resulted in a level of circulating vitamin D greater than 50 nmol/L in all women at 6 months and was associated with an improvement in dynamic muscle strength and hip bone density. This lends further support to the well-established need for vitamin D supplementation in elderly institutionalized populations.11
The increase by 6.4% in knee extensor strength obtained here with 6 months of vitamin D supplementation is in line with other studies showing that vitamin D plays a critical role in muscle strength, although the effects in this study appeared somewhat smaller and were seen only for dynamic strength.26–28 Following 1 year of vitamin D and calcium supplementation (daily 800 IU and 1000 mg, respectively), Pfeifer and colleagues reported an 11.5% increase in isometric knee extensor strength in older subjects with mean age of 77 years.27 In elderly woman with a mean age of 85 years, 12 weeks of daily treatment with 1200 mg of calcium and 800 IU of vitamin D resulted in an 8.5% increase in isometric knee extension strength.12 In a study by Verhaar and colleagues in vitamin D–deficient women over 70 years of age, 6 months of vitamin D supplementation increased isometric knee extension strength by 11.5% compared with controls.26 In contrast, Bunout and colleagues found an 8% decrease in isometric quadriceps strength following 9 months with daily doses of vitamin D of 400 IU and of calcium of 800 mg,29 supporting the concept that a vitamin D dose of at least 800 IU may be required.
In addition to differences in vitamin D doses, the difference in muscle-strength response to vitamin D supplementation in different studies is likely due to a combination of differences in measurement techniques (handheld dynamometer versus isokinetic dynamometer or leg press), age, and serum vitamin D level at baseline.
The increases in muscle strength and function have been ascribed to binding of ligand to specific vitamin D receptors found in human skeletal muscle that promotes protein synthesis and cellular growth.26–28 Vitamin D supplementation for 3 months in a small, uncontrolled study resulted in significant increases in the relative number and size of type II muscle fibers in elderly women,30 whereas 1000 IU of vitamin D a day in elderly stroke survivors increased type II muscle fiber mean diameter by 2.5-fold over a 2-year period.31 In this trial, no muscle hypertrophy of the lower limb was seen after 6 months of vitamin D supplementation.
The small but significant improvements in hip BMD during calcium and vitamin D supplementation in our study (+0.88%) are consistent with previous studies. In untreated elderly women, a continued decline in bone density has been well documented.11 Vitamin D deficiency is known to reduce calcium absorption and induce a rise in parathyroid hormone (PTH) levels, leading to an increase in bone remodeling.8, 32 Evidence from several randomized, controlled trials in older women suggests a similar positive effect of vitamin D supplementation on BMD.9, 11, 33, 34 For example, Ooms and colleagues found a net increase in femoral neck BMD of 1.8% compared with controls following 1 year of 400 IU of vitamin D daily in women aged 70 years and older, with an additional increase of only 0.2% in the second year, underscoring the relatively fast response of bone to vitamin D supplementation.33 Likewise, Dawson-Hughes and colleagues found an increase of 0.64% at the femoral neck following 1 year of 700 IU of vitamin D combined with calcium.9 In order to optimize its effects on bone density and its antifracture efficacy in elderly people, several studies provided evidence that vitamin D must be combined with calcium.35
Recent data suggest that an oral vitamin D dose of 400 IU is not sufficient for fracture prevention and support the use of 700 to 800 IU of vitamin D to reduce fracture risk in elderly women.36 The role of even higher doses of vitamin D in providing additional musculoskeletal benefits remains unclear. Based on the relationship between serum 25(OH)D, BMD, bone turnover, lower extremity function, and falls, current evidence suggests that, at least from a musculoskeletal perspective, 50 nmol/L is the appropriate serum threshold to define vitamin D insufficiency.37 Supplementation therefore generally should aim to increase 25(OH)D levels within the 50 to 75 nmol/L range. As confirmed in our trial, this level can be achieved with a dose of 800 IU/day of vitamin D. At the 6-month end point of this trial, patients on high-dose vitamin D had 20% higher vitamin D levels than those on conventional doses, but this significant difference did not result in further improvements in muscle function and hip BMD.
WBV training led to significant improvements in dynamic muscle strength (+7.9%, p < .001), as well as in total-hip BMD (+ 0.75%, p < .001), with a statistically not significant improvement in isometric muscle strength (+4.48%, p = .184). However, none of the musculoskeletal parameters showed a significant difference between the WBV group and the no-exercise group. The findings indicate that, in institutionalized older women over 70 years of age, 6 months of WBV training does not provide an additional musculoskeletal benefit over vitamin D supplementation. For ethical reasons, no WBV training group without calcium and vitamin D supplementation was included in the study. Therefore, it is difficult to unravel at this stage the unique contribution of both interventions to the improvements in musculoskeletal parameters. Although we did not include a control group without training and vitamin D supplementation, the musculoskeletal improvements found in this study contrast with the expected and well-documented age-related annual declines of, on average, 1.5% in muscle strength38 and 3% in hip BMD, respectively,4, 5 in this type of population older than 70 years of age.
Overall, the gains in muscle strength and bone density in the WBV women in this 6-month study (mean age 80 years; +4.5% in isometric strength, + 7.9% in dynamic strength, and + 0.75% in hip BMD, respectively) were smaller than the improvements found previously following 1 year of training in community-dwelling older men (mean age 67 years, + 9.8% in isometric strength) and following 6 months of training in older women (mean age 64 years, +15% in isometric strength, + 16% in dynamic strength, and + 0.93% in hip BMD, respectively).14–16 Recently, Machado and colleagues found a 38% increase in isometric strength of the lower limb, as measured by a leg press, following 10 weeks of WBV training (of higher intensity) in older women of similar age as those in this study (mean age 79 years).39 This apparent blunting of the treatment effect and the lack of change in muscle mass in this study may be due to a variety of factors. Because of the old age of the study population, the intensity and volume of the WBV program were increased very carefully and relatively slowly to avoid major overload of the musculoskeletal system. The intensity and volume of the program clearly were lower than in previous studies14–16 and may not have allowed the optimization of the bone and muscle response. The amplitude of the vibrations remained low (<2.2g), and it is known that larger amplitudes result in stronger reflexive muscle contractions.40 The vibration training sessions lasted maximally 15 minutes. Not all women were able to perform one-legged squat exercises, which have been shown to be most effective to stimulate muscle activity owing to WBV.41 The load of the WBV program was lower than 60% to 80% of the repetition maximum recommended by the American College of Sports Medicine to induce hypertrophic responses in resistance-trained older adults.42 A recent study by Machado and colleagues in a similar age group but using a higher load of training (involving high-amplitude vibrations as well, training five times instead of three times per week, and including longer training sessions) resulted in significant strength increases, providing additional support to the hypothesis that the conservative approach with low loading in the current WBV training program contributed significantly to the lower gains in strength compared with previous studies.39 In addition, elderly institutionalized women may be less sensitive to the vibratory stimulus owing to, for example, a decline in the number of muscle spindles,43 resulting in a reduced response to loading of the muscle. Finally, muscle plasticity in old age may be limited.44
This study has several limitations that need consideration. Given the strict inclusion and exclusion criteria for participation in WBV training, the subject sample may not be representative of the overall institutionalized elderly population. Only 18 of 111 patients suffered a moderate to severe degree of frailty, as assessed by the PPT.23 The wide variation in performance in this population and the relatively small number of participants per group may limit our ability to document significant differences. Results were obtained in the context of a 6-month trial, and the clinical effects of long-term WBV in this cohort remain unknown.
We conclude that in institutionalized older women over 70 years of age, the WBV training program described herein does not provide additional musculoskeletal benefit over vitamin D supplementation. Compared with conventional doses of vitamin D (880 IU), a higher dose of 1600 IU induced significantly higher levels of circulating vitamin D but was not more efficient in enhancing either muscle mass or strength or increasing hip BMD in this population.
We thank all the women for participating in this study and also acknowledge Edzard Zeinstra for logistical support. This work was supported by Grants G-0488–08 and G-0521–05 from the Fund for Scientific Research (FWO-Vlaanderen) to SB, SV, CD, and ALC. SB is senior clinical investigator of FWO and holder of the Leuven University Chair in Gerontology and Geriatrics. We also would like to thank Heike Bischoff, Centre on Aging and Mobility, University of Zurich, Switzerland, for critically reviewing the manuscript.