VITAMIN D STATUS IN RELATION TO POSTURAL ... - mna … · Amongst them, postural instability (PI) is a common and challenging risk factor due to major difficulties in its identification

Introduction

The relationship between vitamin D deficiency and falls riskis widely accepted (1). Vitamin D deficiency has beenassociated with poor neuromuscular function, whichpredisposes to falls (2, 3). Correspondingly, vitamin Dsupplementation at a dose that corrects serum concentration of25(OH)-vitamin D3 [25(OH)D3] to levels higher than 75nmol/L has shown to decrease the incidence of falls in olderpersons by improving muscle performance and muscle mass(4).

There is evidence suggesting that the effect of vitamin D onfalls goes beyond its effect on muscle mass and muscleperformance (3). A study by Bischoff-Ferrari et al. (5) hasreported that, in addition to its effect on muscle, fall preventionby vitamin D could be mediated by a change in postural anddynamic balance. Participants received 1,200 mg of calcium +/-vitamin D (800 IU cholecalciferol) daily for 3-months. Balancewas assessed using an electronic device attached to the lowerback of the participants while performing static and dynamicbalance exercises. Participants were followed for 3 months to

determine the incidence of falls. The investigators concludedthat, of the observed 60% reduction in the rate of falls byvitamin D plus calcium supplementation, 22% of the treatmenteffect was explained by a change in postural balance and up to14% by dynamic balance. This evidence suggests that lowlevels of vitamin D could be associated with impaired posturalcontrol, a hypothesis that remains to be tested using a moreprecise method for balance assessment.

There are numerous causes and risk factors for falls in olderpersons (6). Amongst them, postural instability (PI) is acommon and challenging risk factor due to major difficulties inits identification and treatment (7, 8). PI occurs as consequenceof degenerations in visual and vestibular sensory system,degeneration in proprioception and impairments in centralprocessing, or a combination of these factors (7). PI is commonin several neurodegenerative diseases including Parkinson’sdisease, progressive supranuclear palsy, cerebellar diseases andvestibular dysfunction (7, 8). In addition, since slow gait andshort steps are thought to improve stability against balancethreats (9), slow gait velocity (GV) is therefore considered asan indicator of PI (7, 9). Finally, PI is also associated with fear

VITAMIN D STATUS IN RELATION TO POSTURAL STABILITY IN THE ELDERLY

D. BOERSMA1, O. DEMONTIERO1,2, Z. MOHTASHAM AMIRI3, S. HASSAN1, H. SUAREZ4, D. GEISINGER4, P. SURIYAARACHCHI2, A. SHARMA1, G. DUQUE1,2

1. Department of Geriatric Medicine, Nepean Hospital, Penrith, NSW, Australia 2751; 2. Ageing Bone Research Program, Sydney Medical School-Nepean, The University of Sydney,Penrith, NSW, Australia 2751; 3. Medical Faculty of Guilan University, Rasht, Iran; 4. British Hospital, CLAEH School of Medicine, Montevideo, Uruguay. Correspondence to: A/Prof.Gustavo Duque, MD, PhD, FRACP, Ageing Bone Research Program, Sydney Medical School Nepean, The University of Sydney, PO Box 63 Penrith NSW 2751, Australia, Tel: +61 2

4734 4278; Facsimile: +61 2 4734 2614, Email: [email protected]

Abstract: Objectives: Postural instability (PI) is an important risk factor for falls, especially in the frail olderpopulation. In this study, we investigated the impact of vitamin D deficiency on PI in a sample of communitydwelling older subjects. Our objective was to determine the potential association between vitamin D deficiencyand PI in older fallers. Design: Cross-sectional study. Setting: Falls and Fractures Clinic, Department of GeriatricMedicine, Nepean Hospital, Penrith, Australia. Participants: One hundred and forty-five adults aged 65 yearsand older who have had at least one episode of a fall within the six months prior to assessment at the Falls andFractures Clinic. Measurements: Serum 25(OH) vitamin D3 [25(OH)D3] and parathyroid hormoneconcentrations were determined at baseline. Subjects were separated into 3 groups based on serum 25(OH)D3levels with the following cut-off values: < 30 nmol/L (deficient), 30-50 nmol/L (insufficient) and > 50 nmol/L(normal). Other baseline measurements included body mass index, mini-nutritional assessment, grip strength,serum calcium concentration and creatinine clearance, which were used as covariables. PI was assessed using acomputerized virtual reality system (Medicaa, Uruguay). Measured parameters included limits of stability (LOS)and centre of pressure (COP) under eyes closed on foam (ECF) and visio-vestibular stimulation. The estimatedswaying area, computed from the ellipse of confidence under eyes closed standing on foam (ECF), was also usedas a PI parameter. Gait velocity (GV) was measured using a GaitRITE walkway system. Results: Posture wasimpaired in vitamin D deficiency (<30 nmol/L) as indicated by lower LOS (90 +/- 18), higher ECF (25 +/- 10)and slower GV (55 +/- 7) as compared with the insufficient and normal groups. After adjustment fordemographic, biochemical and anthropometric variables, vitamin D deficiency significantly correlated with lowLOS and high COP under ECF. Conclusion: Low levels of vitamin D were associated with PI. This associationcould also have an effect on slow GV and increased risk of falls. In conclusion, using an objective method tomeasure balance in older fallers we have identified a novel role of vitamin D in balance control. Prospectivestudies are required to confirm the effect of vitamin D on PI and elucidate the mechanisms of this association.

Key words: Vitamin D, balance, falls, elderly, postural instability, gait velocity.

270

The Journal of Nutrition, Health & Aging©Volume 16, Number 3, 2012


Received January 31, 2011Accepted for publication May 26, 2011

17 DUQUE/p/c_04 LORD_c 05/03/14 09:15 Page270

of falling, which significantly affects the patients’ quality of lifeand predisposes them to falls (10). Interestingly, PI frequentlyoccurs in the general population of older persons in the absenceof a defined neurodegenerative or any other disease. Althoughthis type of PI has been classified as “primary posturalinstability” (8), this type of PI could be secondary to otherunexplored conditions such as vitamin D deficiency.

In fact, a recent experiment in an animal model hassuggested that vitamin D may have an effect on severalcomponents of posture control including a direct effect on thevestibular system. Using vitamin D receptor mutant mice,Minasyan et al. (11) have reported that the mutant mice showedseveral vestibular dysfunctions including shorter latency to fallfrom the rotarod, smaller fall angle in the tilting box test, andaberrant poor swimming. This basic science evidence suggeststhat normal vitamin D signaling is required in balance controland thus normal serum concentrations are required to maintainpostural stability and balance independently of changes inmuscle mass or strength.

In this study, we used a novel method of assessing PI toinvestigate the impact of vitamin D deficiency on indicators ofPI in a sample of community dwelling older subjects. Ourobjective was to determine the potential association betweenvitamin D deficiency and PI in older fallers and to establish thebasis for future clinical intervention trials.

Methods

Study population – We studied a convenience sample of 145subjects (65 years and older) attending the Falls and FracturesClinic at Nepean Hospital in Penrith (Australia) betweenJanuary 2009 and June 2010. Participants attended the clinicafter suffering at least one fall within the 6 months prior to theassessment. A population of older fallers was selected not onlyto mimic the subjects’ characteristics of a previous study (5),but also because of the higher risk of further falls and higherprobability of identifying PI in this particular population.Exclusion criteria were: (a) severe visual impairment, (b)inability to ambulate independently with a cane or walker, (c)inability to stand unaided for 60 seconds, (d) score of <22 in theMini Mental State Examination, (e) Parkinson’s disease or anyneuromuscular conditions, and (f) inability to understand oranswer the study questionnaires. Participants received a fullmedical examination at our clinic including structuredquestionnaires, information about chronic diseases, physicalexamination and anthropometric measurements. The study wasconducted in accordance with the ethical standards set forth inthe Helsinki declaration (1983). The local ethics committee atNepean Hospital approved the project.

Postural assessment – For the purposes of this study, weused the Medicaa Balance Rehabilitation Unit (BRU) (Medicaa,Uruguay), a recently validated and reliable method to assess PIthat includes variable somatosensory, visual and vestibularconditions (12-15). Briefly, postural control responses todifferent types of visual and visual-vestibular stimulation arestudied on standing surfaces of different firmness. The patient

receives visual stimulation through virtual reality goggleseliciting different oculomotor reflexes (smooth pursuit,saccades, optokinetic nystagmus) and moves the head in threeplanes (yaw, roll and pitch). With the information receivedfrom a head-tracker, the software updates the visual stimulationto have a proper interaction with retinal image displacement asoccurs in real life. Online digital recording of posturalresponses is performed in a force platform, either on a firmsurface or on foam for the different sensory conditions. Theposturography report is automatically generated and includeslimits of stability (LOS) and centre of pressure (COP) at 6different conditions: open eyes and eyes closed on hard surface,eyes closed on foam, and three different visual stimuli using the3D virtual reality goggles (Saccadic, optokinetic stimulationand visual vestibular stimulation). A software programproduces a report showing all the indicators of balanceperformance. The assessment takes about 30 minutes toperform.

Although this system has been validated as a useful tool forbalance assessment and balance re-training at different clinicalsettings including patients with Parkinson’s Disease (12), PI(13, 14) and vestibular disorders (16, 17), for the purposes ofthis study, we performed our own evaluation by scoring a groupof 105 subjects with normal serum levels of vitamin D assessedat our Falls and Fractures Clinic in 2010. Two differentevaluators assessed the patients using the BRU system.Interrater reliability was measured with the Kappa statistics andIntraclass Correlation Coefficients (ICCs). The mean values ofthe LOS scored by the 2 evaluators were 155±22.9 and158±22.3, respectively. Kappa score for LOS was 0.92.Intraclass correlation coefficient for the LOS score wasexcellent (ICC=0.99 with 95% confidence interval, 0.98-0.99).An excellent internal consistency was found within the LOSscore (Cronbach Alpha =0.9).

After our own documentation of the validity of this test, thefollowing parameters were obtained by BRU assessment of ourstudy population:

a- Limits of stability (LOS): The LOS is used to estimate themaximum excursion that the subject can displace his or herbody's COP. Under an inverted pendulum hypothesis, subjectsare asked to lean their bodies forward, backwards, and to eachside using only ankle strategies. By keeping the rest of the bodystraight (no head or hip movements) the dynamics of themovement are those of the inverted pendulum. Subjects areasked to lean, reaching as far as they can without lifting ormoving their feet and keeping their arms at their sides. The firstthree trials were used as a demonstration. To estimate the LOSarea we take the maximum excursion in all directions. Theanterior-posterior direction gives one axis (A), the medial-lateral the other axis (B), and we approximate an ellipse withthese two axes. Based on previous reports in similarpopulations (12-15), a normal value for LOS was established as> 174 cm2.

b- Posturography: For each sensory condition, the area of theCOP was calculated from the ellipse of confidence (CE) at 95%

JNHA: GERIATRIC SCIENCE


271


as:

As with the values for LOS, based on previous reports (12-15), a COP lower than 20 cm2 was considered normal.

Definition of falls – Falls were defined as “unexpected andinvoluntary loss of balance, causing the person an undesiredcontact with the ground” (18). The occurrence of falls wasassessed in a retrospective manner asking the participant, 1)whether they have suffered a fall and, 2) the number ofexperienced falls during the last six months.

Gait assessment – A GAIT Rite® (CIR Systems Inc,Havertown, PA) instrumented walkway (810 cm × 89 cm ×0.625 cm, sample rate = 80 Hz) was positioned along a straightsection of the walkway to record spatiotemporal gait data.Three trials were recorded and standard deviation (SD) valueswere calculated for GV.

Grip strength – Grip strength was measured following theGronigen Elderly Test using a Smedley Hand Dynamometer(19). Briefly, the subject held the dynamometer in the hand tobe tested, with the arm at right angles and the elbow by the sideof the body. The handle of the dynamometer was adjusted asrequired - the base rests on the first metacarpal (heel of palm),while the handle rested on the middle of the four fingers. Whenready the subject squeezed the dynamometer with maximumisometric effort, which was maintained for about 5 seconds. Noother body movement was allowed. The subject was stronglyencouraged to give a maximum effort. Following a practicetrial, the best of three attempts with 30 seconds rest betweenthem was recorded.

Serum measurements - Venous blood was collected fromresting subjects for the measurement of serum 25(OH)D3,parathyroid hormone (PTH), calcium, creatinine and albumin.Serum 25(OH)D3 concentration was measured bychemiluminescence using the Elecsys 25(OH)D3 assay(Roche). The intra- and interassay precisions were respectively7.5 % and 10.6 %, (detection range=10-132 nmol/l). Intact PTHwas measured by immunochemoluminometric assay (Immulite2000; normal range= 0.5-76.6 pmol/L. The intra- and inter-assay precisions were 7% and 5% respectively. Serum calcium,albumin and creatinine were determined using automatedstandard laboratory methods. Because of the high prevalence ofhypoalbuminemia in older adults, the serum concentration ofalbumin and calcium were used to correct the calcium value(calcium corrected value = Ca + 0.8 [40-albumin]). Thecalcium corrected value was used in the subsequent analysis.The clearance of creatinine was calculated from the Cockcroftformula ([(140-age in years) x weight (Kg)/ 72 x creatininemol/l]). All measurements were performed at the NepeanHospital, Penrith, Australia.

Clinical covariates – Age at baseline evaluation,mininutritional assessment (MNA), geriatric depression scale(GDS), and use of calcium supplementation were used asclinical confounders in data analysis. BMI was calculated as

weight (kg)/[height (m)]2. Weight was measured with a set ofcalibrated weigh scales and height with a digital stadiometer.

Statistical analysis – The subjects’ characteristics weresummarized using means and standard deviations orfrequencies and percentages, as appropriate. The normality inthe distribution of variables was verified with skewness andkurtosis tests. Serum 25(OH)D3 and PTH concentration,clearance and BMI were successfully normalized using alogarithmic transformation. Subjects were separated into threeconventional groups based on serum 25(OH)D3 concentration[20] with the following cut-off values: Deficient= < 30 nmol/l,Insufficient= 30-50 nmol/l, and normal= > 50 nmol/l. Firstly,comparisons were performed using the independent samplestest, the Kruskal-Wallis test, one-way analysis of variance(ANOVA) or Chi-square test, as appropriate. Adjustment wasperformed with subjects’ baseline characteristics.Subsequently, Pearson or Sepearman’s (for non-parametricvariables) correlation coefficients were used to determine theassociations between demographic, biochemical, posture andgait parameters. p-values < 0.05 were considered as statisticallysignificant. All the statistics were performed using SPSSSoftware version 19.

Results

Demographic, anthropometric, and health characteristics ofthe participants by their vitamin D status are described in Table1. Amongst the 145 participants (73-88 years old), 21% werevitamin D deficient, 19% were insufficient and 40% showednormal serum concentrations of 25(OH)D3. No differenceswere found between the three groups regarding age, gender,BMI, MNA, albumin, creatinine clearance, PTH, correctedcalcium, grip strength and GDS. A significant difference in thenumber of falls was found between deficient versus theinsufficient and normal vitamin D groups (7 ± 2, 2 ± 1 and 3 ±1 respectively, p = 0.01).

Table 1Characteristics of the study participants by vitamin D status

Variables Vitamin D Vitamin D ≥ 30 Control Group P value*< 30 nmol/L and ≤50 nmol/L >50 nmol/L

(n = 38) (n =28) (n =79)

Age (years) 79.7 ± 7 78.5 ± 7 79.2 ± 9 NSGender (% women) 57 57 64 NSBody Mass Index (Kg/m2) 30 ± 5 29 ± 7 26 ± 4 NSMini-nutritional 15 ± 4 14 ± 4 16 ± 4 NSAssessment (score)Albumin (g/L) 41.8 ± 2 41.8 ± 4 42.3 ± 2 NSVitamin D (nmol/L) 22 ± 5 41± 5 81 ± 22 a, bParathyroid hormone 7.5 ± 2.7 6 ± 3.5 6 ± 5.2 NS(pmol/L)Corrected Calcium 2.3 ± 0.1 2.4 ± 0.1 2.3 ± 0.1 NS(mmol/L)Falls (last 6 months) 7 ± 2 2 ± 1 3 ± 1 bGrip strength (Kg) 17 20 15 NSGDS (score/15) 6 5 5 NS

Figures are means ± SD; * independent sample t test. a P<0.05 for deficient vs. insufficientgroup; b P<0.05 for insufficient vs normal group.

We then evaluated the differences in posture and gaitparameters according to the levels of serum 25(OH)D3. Only



272


273



those parameters that have been associated with increased riskof falls (7) were selected for further analysis. Figure 1 showsthe mean difference between deficient, insufficient and normalindividuals. The vitamin deficient group showed significantalterations in LOS (90 +/- 18), ECF (25 +/- 10) and GV (55 +/-7) as compared with the insufficient and normal groups(p<0.05). Furthermore, the effect of 25(OH)D3 concentrationon GV, grip strength, MNA, GDS, BMI, and parameters ofpostural stability was investigated (Table 2). We observed aninverse relation between 25(OH)D3 concentration and ECF (r= –0.188) and BMI (r = –0.325), and a significant correlationbetween serum 25(OH)D3 and GV (0.316) and LOS (0.305).All this correlations were confirmed by both univariatemultivariate analyses (Table 2).

Table 2Regression analysis of serum concentrations of vitamin D,subjects’ clinical characteristics and markers of postural

stability and gait

Univariate Multivariate 1

Coefficient P Coefficient P

BMI -0.325 <0.001 -0.173 0.048Grip strength -0.118 NS -0.61 NSMNA 0.068 NS 0.12 NSGait velocity 0.316 <0.001 0.26 0.045GDS -0.153 NS -0.08 NSLimits of stability 0.305 <0.001 0.42 0.029ECF -0.188 0.040 -0.16 0.044

1. Covariates considered were sex, age, body mass index (BMI), geriatric depression scale(GDS), mininutritional assessment (MNA), serum parathyroid hormone (PTH) and 25-hydroxyvitamin D.

Figure 1Comparison between means ± SD for balance and gait

parameters according to vitamin D status. Deficient subjects(<30 nmol/L) have significantly lower limits of stability (LOS)

(A) and higher sway in the eyes closed on foam (ECF)condition (B). In addition, deficient subjects show slower gait

velocity (GV). No differences were found in the subjects’ COP.for visual vestibular conditions (average of three different

conditions). * P<0.05, ** P<0.01

Furthermore, after adjustment for demographic andanthropometric variables, slow GV significantly correlated withlow LOS (r2 .58, p=0.001) and high ECF (r2 .42, P=0.01).Finally, COP for visual vestibular condition was found normalin the three groups.

Discussion

People aged over 65 years are at greatest risk of sustainingan injury from a fall. Vitamin D deficiency, a condition ofcommon occurrence in older persons, has been associated withchanges in gait, muscle strength, and neuromuscular integrationthus predisposing to falls (3). However, the relationshipbetween vitamin D deficiency and postural changes remainspartially assessed. Using a novel and reliable technique toassess posture and balance, in this study we have found thatvitamin D deficiency is associated with PI and slow GV, whichmay explain the high occurrence of falls in a particularpopulation of subjects with vitamin D deficiency but withnormal nutritional status, absence of other major risk factors forfalls and normal grip strength.

Impaired balance has been associated with nutritional status,muscular weakness and PI in older fallers (7, 21). Consideringthe physiological role of vitamin D in the neuromuscularsystem, the relationship between low vitamin D and alterationsin postural control under normal muscular strength conditionsshould be apparent, however the evidence supporting thisrelationship is scarce. In fact, there is a particular subset ofvitamin D deficient subjects whom, such as the presentpopulation, suffer frequent falls while showing either noabnormalities in their grip strength or any neurological orsensorial deficits. Based on this subpopulation, we thenhypothesized that a comprehensive clinical and posturalassessment of ambulatory dwelling older fallers woulddemonstrate a new role of vitamin D deficiency in thepathogenesis of PI and falls in older persons, independently oftheir nutritional status and grip strength.

Overall, PI has been closely associated with higher risk forfalls and fractures (7, 22). Nguyen et al (23) have reported anassociation between PI and fractures amongst the participantsof the Dubbos osteoporosis study. In their report, the authorsindicated that a woman with a bone mineral density in thelowest quartile in the hip, together with high body sway had a8.4% probability of fracture per annum representing an almost14-fold increase in risk of fracture compared with a woman inthe highest bone mineral density quartile with low posturalsway.

In terms of identification of PI, posturography constitutes themost reliable test for the diagnosis of PI at the clinical settingwhen combined with comprehensive clinical history andphysical examination (13, 24). Some of the advantages ofposturography include: (a) makes an appropriate differentialdiagnosis in patients presenting with falls or balanceimpairment; (b) reliably identifies those subjects who are at risk


of falling; (c) objectively and quantitatively documents theoutcome of therapeutic interventions; and (d) could provide abetter pathophysiological understanding of PI and falls, as abasis for the development of improved treatment strategies toprevent falling. In each of these fields, posturography offersseveral theoretical advantages and, when applied correctly,provides a useful tool to gain a better understanding ofpathophysiological mechanisms in patients with balancedisorders, at the group level.

For the purposes of this study, we used a recently validatedand reliable method to assess PI that includes variablesomatosensory, visual and vestibular conditions (12-14). Inaddition, despite recent reports on the association betweenalterations in GV and vitamin D deficiency (25), in our studywe complemented this evidence by also assessing theassociation between PI, slow GV and vitamin D deficiency,which combined may have a significant effect on increasing fallrisk in older persons. Our data indicate that subjects withvitamin D deficiency not only suffer of a higher number of fallsbut also showed two of the major parameters of PI namely lowLOS and high COP under ECF condition. In addition, vitaminD deficient individuals showed slower GV as compared withinsufficient and normal individuals, which correlates withalterations in postural control. Interestingly, the high prevalenceof PI in the vitamin D deficient individuals was independent ofany other demographic, anthropometric, functional ornutritional parameters suggesting a clear association betweenvitamin D deficiency and PI in this particular population.

One of the challenges of the present study was thedetermination of normal levels of LOS and ECF in thisparticular population of older fallers. The majority of previousstudies using BRU (12-15) have been performed in youngerindividuals whose parameters of normality could be higher thanour older population. To solve this issue, further studies lookingat a higher number of normal older individuals should beperformed in the future. Nevertheless, our data clearlydemonstrate that subjects with normal concentrations ofvitamin D performed much better in their BRU assessment ascompared with the deficient group.

A major strength of our study is the use of an accuratemethod to perform postural assessment in older fallers in a safeenvironment. The relationship between alterations in posturalcontrol and nutritional status has been partially assessed in onecross sectional (26) and one double blind randomizedcontrolled trial (5). In those studies, balance and posture controlwere assessed using indirect methods such as Berg BalanceTest and postural/dynamic tasks respectively. Although bothstudies conclude that there is a correlation between nutritionalstatus (including vitamin D) and balance performance, thelimited reliability of the assessing methods affects the validityof their conclusion.

A major limitation of our study is that self report was used tocalculate the number of falls, which is limited by a potentialrecall bias. However, our findings agree with previous reports

on the prevalence of falls in vitamin D deficient individuals(27). A second potential limitation is that institutionalized andcognitively impaired subjects, two populations at higher risk offalls, were not included in this study. This limitation is due tologistical issues since mobility and good cognition areimportant requirements to use our virtual reality system.Finally, and due to the cross sectional nature of this study andthe studied population, an alternative explanation for the data isthat subjects with PI have more disability due to this condition.Nevertheless, the demographic characteristics shown in table 1and the use of limited mobility as an exclusion criteria suggestthat all our three groups are very homogeneous with theexception of having significant differences in their serumvitamin D, GV and PI, which were the variables of interest inthe present study.

In conclusion, we have found that PI is associated with lowconcentrations of vitamin D in community dwelling olderfallers independently of their nutritional or functional status.The mechanisms explaining this association and the effect ofcorrecting vitamin D concentrations in patients with PI shouldbe subject of future studies. Considering that PI could be aconcealed risk factor for falls and fractures in older persons,appropriate assessment and effective interventions for PI arehighly needed.

Acknowledgements: This study was supported by a research grant from the NepeanMedical Research Foundation. A/Prof. Duque holds a Fellowship from the University ofSydney Medical Research Foundation. Dr Demontiero holds a scholarship from TheRebecca Cooper Medical Research Foundation.

References

1. O'Donnell S, Moher D, Thomas K, Hanley DA, Cranney A (2008) Systematic reviewof the benefits and harms of calcitriol and alfacalcidol for fractures and falls. J BoneMiner Metab. 26:531-542

2. Montero-Odasso M, Duque G (2005) Vitamin D in the aging musculoskeletalsystem: an authentic strength preserving hormone. Mol Aspects Med. 26:203-219

3. Rossat A, Fantino B, Nitenberg C, Annweiler C, Poujol L, Herrmann FR, Beauchet O(2010) Risk factors for falling in community-dwelling older adults: which of themare associated with the recurrence of falls? J Nutr Health Aging. 14:787-791.

4. Bischoff-Ferrari HA, Dawson-Hughes B, Staehelin HB, Orav JE, Stuck AE, TheilerR, Wong JB, Egli A, Kiel DP, Henschkowski J (2009) Fall prevention withsupplemental and active forms of vitamin D: a meta-analysis of randomisedcontrolled trials. BMJ. doi: 10.1136/bmj.b3692

5. Bischoff-Ferrari HA, Conzelmann M, Stähelin HB, Dick W, Carpenter MG, AdkinAL, Theiler R, Pfeifer M, Allum JH (2006) Is fall prevention by vitamin D mediatedby a change in postural or dynamic balance. Osteoporos Int. 17:656-663.

6. Delbaere K, Close JC, Menz HB, Cumming RG, Cameron ID, Sambrook PN, MarchLM, Lord SR (2008) Development and validation of fall risk screening tools for usein residential aged care facilities. Med J Aust. 189:193-196.

7. Horlings CG, van Engelen BG, Allum JH, Bloem BR (2008) A weak balance: thecontribution of muscle weakness to postural instability and falls. Nat Clin PractNeurol. 4:504-515.

8. Djaldetti R, Lorberboym M, Melamed E (2006) Primary postural instability: a causeof recurrent sudden falls in the elderly. Neurol Sci. 27:412-416.

9. Espy DD, Yang F, Bhatt T, Pai YC (2010) Independent influence of gait speed andstep length on stability and fall risk. Gait Posture. 32:378-382

10. Robinson K, Dennison A, Roalf D, Noorigian J, Cianci H, Bunting-Perry L, MobergP, Kleiner-Fisman G, Martine R, Duda J, Jaggi J, Stern M (2005) Falling risk factorsin Parkinson's disease. NeuroRehabilitation. 20:169-178.

11. Minasyan A, Keisala T, Zou J, Zhang Y, Toppila E, Syvälä H, Lou YR, Kalueff AV,Pyykkö I, Tuohimaa P (2009) Vestibular dysfunction in vitamin D receptor mutantmice. J Steroid Biochem Mol Biol. 114(3-5):161-166.

12. Suarez H, Geisinger D, Suarez A, Carrera X, Buzo R, Amorin I (2009) Posturalcontrol and sensory perception in patients with Parkinson's disease. Acta



274


Otolaryngol. 129:354-360.13. Suarez H, Arocena M, Suarez A, De Artagaveytia TA, Muse P, Gil J (2003) Changes

in postural control parameters after vestibular rehabilitation in patients with centralvestibular disorders. Acta Otolaryngol. 123:143-147.

14. Suarez H, Muse P, Suarez A, Arocena M (2000) Postural behavior responses tovisual stimulation in patients with vestibular disorders. Acta Otolaryngol. 120:168-172.

15. Suarez H, Geisinger D, Suarez A, Carrera X, Spiller P, Lapilover V (2008) Posturalstrategies in normal subjects and in patients with instability due to central nervoussystem diseases after sudden changes in the visual flow. Acta Otolaryngol. 128:398-403.

16. Suarez H, Arocena M, Suarez A, De Artagaveytia TA, Muse P, Gil J (2003) Changesin postural control parameters after vestibular rehabilitation in patients with centralvestibular disorders. Acta Otolaryngol. 123:143-147.

17. Suarez H, Muse P, Suarez A, Arocena M (2000) Postural behavior responses tovisual stimulation in patients with vestibular disorders. Acta Otolaryngol. 120:168-172.

18. Lamb SE, Jørstad-Stein EC, Hauer K, Becker C (2005) Prevention of Falls NetworkEurope and Outcomes Consensus Group. Development of a common outcome dataset for fall injury prevention trials: the Prevention of Falls Network Europeconsensus. J Am Geriatr Soc. 53:1618-1622.

19. Soer R, van der Schans CP, Geertzen JH, Groothoff JW, Brouwer S, Dijkstra PU,Reneman MF (2009) Normative values for a functional capacity evaluation. ArchPhys Med Rehabil. 90:1785-1794.

20. Binkley N, Ramamurthy R, Krueger D (2010) Low vitamin D status: definition,prevalence, consequences, and correction. Endocrinol Metab Clin North Am. 39:287-301

21. Horlings CG, van Engelen BG, Allum JH, Bloem BR (2008) A weak balance: thecontribution of muscle weakness to postural instability and falls. Nat Clin PractNeurol. 4:504-515.

22. Bloem BR, van Vugt JP, Beckley DJ (2001) Postural instability and falls inParkinson's disease. Adv Neurol. 87:209-223.

23. Nguyen T, Sambrook P, Kelly P, Jones G, Lord S, Freund J, Eisman J (1993)Prediction of osteoporotic fractures by postural instability and bone density. BMJ.307:1111-1115.

24. Visser JE, Carpenter MG, van der Kooij H, Bloem BR (2008) The clinical utility ofposturography. Clin Neurophysiol. 119:2424-2436.

25. Annweiler C, Schott AM, Montero-Odasso M, Berrut G, Fantino B, Herrmann FR,Beauchet O (2010) Cross-sectional association between serum vitamin Dconcentration and walking speed measured at usual and fast pace among olderwomen: the EPIDOS study. J Bone Miner Res. 25:1858-1866.

26. Shahar D, Levi M, Kurtz I, Shany S, Zvili I, Mualleme E, Shahar A, Sarid O, MelzerI (2009) Nutritional status in relation to balance and falls in the elderly: a preliminarylook at serum folate. Ann Nutr Metab. 54:59-66.

27. Cherniak EP, Florez H, Roos BA, Troen BR, Levis S (2008) Hypovitaminosis D inthe elderly: from bone to brain. J Nutr Health Aging. 12:366-373.



275


Documents

VITAMIN D STATUS IN RELATION TO POSTURAL ... - mna … · Amongst them, postural instability (PI) is a common and challenging risk factor due to major difficulties in its identification