1. Introduction

For more than 30 years, falls have been a leading cause of death among older persons in the United States, and elsewhere ^[1,2]. Among those who survive, many, previously unimpaired, may experience mobility and independence losses, plus a greater risk of premature mortality ^[3].

Fortunately, cumulative evidence indicates several potentially modifiable factors can influence the risk of falling and sustaining a disabling injury. These include, but are not limited to deficient muscle strength, confusion, sensory losses, and poor postural control or balance impairments ^[1,3,4,5].

In particular, among recent discussions concerning falls risk factors among the elderly, the question of whether there is a possible link between any increased risk of falling as a result the influence vitamin D on balance capacity has been raised. If it can be shown that vitamin D, a hormone associated with many important body functions ^[2,4] and that can be delivered in the form of a daily supplement, or via and intramuscular injection, the ingestion of certain foods, and/or sunlight exposure is a powerful mediating force that influences balance capacity, this may have a highly positive influence on reducing falls risk among the elderly ^[6].

That is, in addition to converging research that implies optimal levels of vitamin D, potentially impact muscle function, bone quality, cartilage metabolism, pain, depression, and comorbid health conditions favorably, the presence of optimal levels of vitamin D may play an important role in impacting balance capacity, thus reducing the risk of falls attributable to balance related impairments. This does not contradict or negate the use of supervised physical activity programs- or multi-component programs or selected therapies such as whole body vibration training ^[1] or environmental modifications ^[4] as being beneficial to reducing falls risk among the elderly, but suggests that instead of costly multidimensional approaches that may still fail to produce the desired outcomes-if the individual is vitamin D deficient, and/or is on psychoactive drugs for depression, and has poor balance capacity, regardless of improved footwear, and dietary practices, vitamin D intake might be favorably modified to influence balance and falls risk in a favorable way.

Consider too, the problems of adhering to recommendations to carry out progressive resistance exercises on a consistent basis, in addition to aerobic, and flexibility exercises, as a falls risk prevention strategy ^[1], among the older adult, especially those who are already health compromised. In addition, older persons at risk for falling may already be vitamin D deficient, thus rendering muscle intervention outcomes suboptimal at best. Moreover, falls can actually occur during exercise if the individual is weak, or if exercise is fatiguing, or if balance is suboptimal due to structural problems. Finally, even if the individual falls and fractures a bone, it is accepted they will be more likely to achieve a better outcome if they do not have any prevailing vitamin D deficiency if compared to those who have a prevailing deficiency.

Even though many researchers have attempted to examine the role of multiple measures applied concurrently to reduce falls risk among the elderly-how these can be applied in real life circumstances with fidelity and what specifically is required in this regard-remains quite vague. There is also no convincing evidence that single measures will not be as effective as multiple measures in efforts to prevent falls among older persons. In addition, what the active ingredient is in multiple directed interventions is not readily discernable in related reports, eg., Palvenen et al. ^[7] and how well these studies control for attention is unclear.

There is further controversy as to the influence of vitamin D supplementation on falls risk [references 8 versus 9], and specifically as to whether balance is positively affected in the presence of adequate vitamin D serum levels ^[6,9]. Also in question are the mechanisms that account for improvements in some balance measures following vitamin D supplementation ^[10] While Muir et al. ^[11] concluded that supplemental vitamin D of approximately 800-1000 IU has consistent balance benefits in older adults, only 7/12 studies in a 2015 a meta-analysis of multifactorial studies to reduce falls reported this to be a fact ^[9]. Before continuing to base recommendations made in the clinic on highly conflicting data, it is our view that the current as well as the past literature should be carefully examined, and some explanation for the conflicting results should be forthcoming.

---

1.1. Aims

This review aimed to access and examine the available information related to the claim that an appropriate daily supplement of vitamin D or efforts to ensure optimal vitamin D serum levels via other methods may go a long way to reducing the risk of falls due to poor balance capacity among older adults. That is, the paper specifically examines if vitamin D supplementation is likely to positively affect balance capacity among older individuals, if they present with any deficiency or insufficiency.

---

1.2. Implications

The question addressed in this review was deemed important to resolve because if proved efficacious, vitamin D supplementation is likely to be highly advantageous clinically because it is easy to adhere to, as well as economically feasible, and practical, when compared to exercise and cognitive approaches employed in falls prevention efforts that are often challenging, time consuming, and carried out inconsistently.

---

2. Materials and Methods

To address the topic highlighted in this present review, a very brief summary of the traditional approaches to falls prevention, followed by the research on vitamin D is discussed. Thereafter, studies that have specifically examined vitamin D levels and their association to balance capacity in older adults are described. To this end, data in primary repositories on the topic at hand were sought using key words such as falls, vitamin D, balance, postural control. Excluded from the detailed descriptive analysis were studies of subjects younger than 60 years of age, those with neurological diseases, research studies conducted prior to 2011, as these have been detailed in Muir et al. ^[11]. Others were excluded if they did not focus on the topic of interest, or were written in a language other than English or were not complete articles. A sample of the extent of the findings conducted in Scopus. Academic Search Complete, Web of Science, PUBMED and Cinahl is shown below and includes the time period of 1980-June, 2016. Both cross sectional, as well as prospective studies, along with observational and controlled studies were deemed acceptable, and only a narrative review of these data was attempted.

---

3. Search Results

Using the search term Falls Prevention, there were 12070 possible PUBMED articles; 7598 in last 10 years; and 4190 in the last 5 years. The search term Vitamin D yielded 68265 articles; 30815 in the last 10 years, and 19462 in the last 5 years. The combination of Vitamin D and Falls Prevention yielded 685 articles, 485 in last 10 years, and 236 in last 5 years. The combined terms Vitamin D and Balance yielded 679 articles in the last 10 years and 391 in the last 5 years. Many articles did not however focus on the topic at hand. Thus one can say that very few articles in addition to those 13 presented by Muir et al. ^[11] prevail, however, all are included in some way in this report.

---

3.1. Falls prevention programs and vitamin D

A number of review articles and stand-alone reports have concluded that it is important to utilize a multifactorial program approach in the context of preventing falls among older adults ^[7] given the multiple determinants of falls risk. While there is reasonable support for this idea, there is a limited understanding of which strategies will yield the desired outcomes most effectively, and why. Among the observations made in this realm Bischoff-Ferrari et al. ^[12] demonstrated a significant impact of vitamin D plus calcium on falls injury rates that was attributable in part to improvements in static and dynamic balance. Kormaz et al. ^[13] too, found vitamin D to be necessary for enhancing muscle strength, range of motion, and balance, which could potentially reduce falling rates among postmenopausal women with osteoporosis.

Thus, similar to exercise, often applied in the context of falls prevention programs, some research shows vitamin D supplementation, may impact positively on several factors often associated with falls risk, including physical and cognitive health in older non-demented individuals ^[14], muscle strength and function ^{[4,15,16,17,18]}, chair rising time ^[4], muscle mass and contractile capacity ^[19], navigational and cognitive performance ^[20]), postural adaptations ^[21], postural sway, and lower extremity and physical performance ^[18] in the elderly ^[22]. Other research shows low vitamin D levels, in contrast, are associated with decreases in muscle mass, strength and contractile capacity, as well as physical performance in older people ^[20] and balance ^[23], and possibly on increased falls risk, but the association between vitamin D and balance performance is not always consistent.

---

3.2. Balance and vitamin D

A fair number of research studies show balance is a strong predictor of falls in later life ^[24], and that balance impairments are associated with increased falls rates ^[25]. Thus treatments than can optimize balance capacity are of high potential import to the well-being of older adults as outlined by Takata ^[22].

But what is the extent of the evidence for this claim? Below are some recent studies categorized as observational versus intervention studies and their findings.

---

3.2.1. Observational studies

Contrary to studies that show a relationship between vitamin D levels and various functional parameters, Mathei et al. ^[26] who investigated the baseline relationship between muscle function and vitamin D status among 367 frail elderly 80 years and older in a prospective study found no significant vitamin D, balance relationship. Only 12.8% of the sample had sufficient vitamin D levels, yet this did not translate into any meaningful association of balance. The static tandem stance balance test-which was assessed as a dichotomized variable may have been too insensitive for assessing challenges or proficiencies in balance capacity during actual functional tasks however, and may warrant more study. Dividing the cohort in to 4 groups of unequal subject numbers based on vitamin D serum levels that may have been less than optimal and who were said to be similar but had somewhat divergent gait scores and hand grip scores may have affected the nature of the associations examined and their observed relationships that did not concur with previous work.

In another study that recently assessed the relationships among vitamin D levels, balance, falls, muscular strength, and quality of life in 46 women with postmenopausal osteoporosis and 46 healthy women, Korkmaz et al. ^[13] reported that vitamin D has a direct effect on balance. In this study, the balance tests used included the Timed Up and Go and Chair Raising test, and the Berg Balance Test, and although there were no group differences observed, after subdividing the patient group, it was shown those with vitamin D levels greater than 15 ng/ml had significantly better balance than those with vitamin D levels lower than 15 ng/ml as shown by the longer chair rise time and rise times in the group with low vitamin D levels.

In support of the aforementioned study findings, Boersma et al. ^[27] who examined 145 community dwelling adults over age 65 with at least one recent falls injury or episode noted their measures of postural instability assessed using a computerized virtual reality system that assessed limits of stability and center of pressure under eyes closed on foam and visio-vestibular stimulation were negatively correlated with prevailing levels of vitamin D after adjusting for demographics, biochemical and anthropometric variables. Similarly Krause et al. ^[28] found postural body sway of 342 older individuals was higher in those with vitamin D deficiency.

Akdeniz et al. ^[29] who evaluated the association between vitamin D and the risk of falling, balance capacity, and lower extremity neuromuscular function among women aged 60 or older also found those with serum vitamin D levels greater than 50.0 nmol/l to have superior balance control. This group used an instrument known as Tetrax posturography, and they classified 200 women based on their vitamin D levels into a hypo-vitaminosis group (less than 50.0 nmol/l) and a normal group (50.0 nmol/l or more). Their data revealed a significant association between the subject’s serum vitamin D levels and their stability scores as well as their lower extremity functional scores, and falling risk.

Menant et al. ^[31] however, found slightly different results in that the presence of a vitamin D deficiency or insufficiency reduced leaning balance, but not postural sway. The results of this study involving a sample consisting of 463 community-dwelling older men and women 70-90 years of age also showed that after controlling for age and body mass, these vitamin D levels and leaning balance measures were more strongly related in men than women.

In related basic research, an important finding that may help to resolve the issue of whether a vitamin D deficiency may indeed affect balance is the observation of the impact of vitamin D on increasing the risk for developing otolith dysfunction of both the utricle and saccule of the inner ear. This was suggested by a study that showed a high prevalence of abnormal ocular vestibular-evoked myogenic potentials (oVEMP) and cervical vestibular-evoked myogenic potentials in the context of vitamin D deficiency. ^[30]. If this can be shown to be a robust finding, it further suggests there is at least one powerful mechanism explaining any probable vitamin D - balance association.

---

3.2.2. Intervention and prospective studies

Among controlled or prospective studies that have examined vitamin D and balance associations, Dukas et al. ^[15] who studied 237 participants with a mean age of 75.9 years who received daily treatment of a form of vitamin D known as alfacalcidol found that when controlling for age, gender and body mass, treatment with vitamin D significantly increased balance performance at 3 months. This effect increased after six months of therapy and was accompanied by a decrease in the absolute number of fallers and falls, compared to the six months before starting the therapy.

Bogaerts et al. ^[1] who compared the effect of a regular dosage versus a higher dosage of vitamin D on 113 older individuals randomized to a vibration exercise group or control group found contrary results. Studying only healthy adults 70 years, they measured dynamic balance along with falls risk before and after six months. No differences in any outcome were predicted by vitamin D dosages, however, although sway velocity improved in the experimental group. There was no sham control group but it still seemed that a link between vitamin D and balance as reported by the Timed get up and Go Test which improved in both experimental and control groups to the same extent could not be discounted.

The outcomes observed by Bogaerts et al. ^[1] were also dissimilar to those of Annweiler et al. ^[21]where higher serum vitamin D concentrations were associated with better balance among older adults with supra-optimal vitamin D status. These were aligned however, with those of Bird et al. ^[25] who found no association between seasonal vitamin D variations and postural sway measures in independently mobile older adults assessed prospectively.

Moreover, a study by Iwamoto and Saito ^[19] who conducted an open-label randomized controlled trial designed to clarify the effect of a vitamin D derivative on body balance found there was no significant improvement in the uni-pedal standing time measure in the experimental group, compared with the control group, even though chair-rising time decreased significantly in that group compared with the control group. In this study, 106 postmenopausal women with osteoporosis, average age 70.8 years were randomized into two equal size groups: a bisphosphonate group (control group) and a bisphosphonate plus vitamin D group. Biochemical markers, uni-pedal standing time-a measure of balance, and five-repetition chair-rising time (a measure of muscle power) were evaluated before and after the 6-month study period. After the 6-month treatment period, the researchers found the bone turnover markers had decreased significantly from the baseline values but this was similar in the two groups. The present study showed that although the intervention improved the chair-rising time of postmenopausal osteoporotic women treated with bisphosphonates, it had no effect on the functional balance measure.

Uusi-Rasi et al. ^[32] however, concluded vitamin D supplementation and exercise recommended for prevention of falls for older people were not efficacious, but that strength and balance training were more helpful. The cohort were all 70 years and older with a falls history who participated in a 2-year randomized, double-blind, placebo-controlled study. The four study groups included a placebo group without exercise, a vitamin D (800 IU/d) group without exercise, a placebo and exercise group, and a vitamin D (800 IU/d) and exercise group. The main outcome assessed monthly was reported falls. Injurious falls and the number of fallers and injured fallers were reported as secondary outcomes. As well, bone density, physical functioning (muscle strength, balance, and mobility), and vitamin D metabolism were assessed. Vitamin D maintained femoral neck bone mineral density and increased tibial trabecular density slightly. However, only exercise improved muscle strength and balance, and vitamin D had no mediating exercise effect on physical functioning.

As outlined by Anek et al. ^[33], the impact of vitamin D supplementation may be dependent on the extent of the dosage or mode of delivery provided, among other factors. This group showed that high supplementary doses of vitamin D2 improved balance ability at the post test on normal stability surfaces when experimental subjects were compared with a control group (p < 0.05). This group divided post-menopausal women into two equal size groups, 26 who received vitamin D supplementation, and 26 who served as a control group. The experimental group received 20, 000 IU of vitamin D2 per week, for a period of 4 weeks. The control group did not receive vitamin D2.

Similarly in a study by Cangussu et al. ^[34], the authors who applied vitamin D supplementation to postmenopausal women fallers found falls rates were almost 50% higher in the control group. They also found the relative risk for recurrent falls was 2.80 times higher for the control group compared to the experimental group. The experimental group who received the supplementation showed a reduction in body sway in both the antero-posterior and latero-lateral directions, which was taken to indicate a positive independent outcome of isolated vitamin D supplementation on postural balance after 9 months, and the significant falls reduction rate. This body of research seems sound because the researchers used a double-blind, placebo-controlled trial design to examine the post-intervention responses of 160 postmenopausal women randomized into two groups: a vitamin D group of 80 adults that received vitamin D3 supplementation of 1, 000 IU/day/orally and a placebo group of 80 women who partook in the study for 9 months. The subjects’ postural balance was assessed using stabilometry and falls incidents were recorded by interviews. The subjects’plasma concentration of vitamin D was measured by high-performance liquid chromatography and after 9 months, the mean values of these assays showed the vitamin D levels increased in the experimental group and decreased in the control group.

Other data have shown that intra muscular vitamin D applications can have a marked effect on balance in vitamin D deficient elderly women ^[35], and that vitamin D supplementation may improve corticospinal neural transmission in older persons ^[36] as well as gait control ^[5].

---

4. Discussion

The recommendation that optimal levels of vitamin D be employed in efforts to prevent falls among older adults is widespread. The possible contribution of improved balance capacity to explain this potential benefit, while grounded in a fairly strong rationale, is less universally demonstrated. Indeed, there are both supportive and non-supportive findings in the recent literature as to whether balance capacity among older adults is heightened or optimized by vitamin D, but it is not clear what explains this difference as the study samples, duration, design, outcomes assessed, vitamin D analogs, definitions, and dosages, and research goals addressed are strikingly diverse. In addition, even among similar study approaches or among positive affirmative studies it is very hard to link the association between balance and vitamin D levels to falls injury rates, as balance tests are not only diverse, but are largely those that capture elements of balance under static or non-functional conditions unrelated to tripping and slipping-associated with most falls that occur during gait (See Box 1). In other cases, tests such as the sit to stand timed tests are used differentially, sometimes to represent balance capacity, or alternately to represent muscle power. Moreover, when falls rate improvements are noted, the use of other falls reduction strategies applied simultaneously and the failure to control adequately for this possibility, as well as the tools used to verify the extent of any falls related injuries, prevents the attribution of any identified balance improvements specifically to vitamin D supplementation, or any related linkage to falls risk. As well, the type of vitamin D correlate being discussed, the modes of obtaining adequate levels of vitamin D, the methods of measuring vitamin D levels, the definition of vitamin D sufficiency versus insufficiency, as well as dosages of vitamin D employed as a falls prevention strategy are generally quite inconsistent, regardless of study design ^[40]. In many cases too, baseline vitamin D levels, adherence rates, prevailing health status, degree of outdoor vitamin D exposure, intake of food based vitamin D components, plus post treatment vitamin D levels have not always been clearly delineated or controlled for ^[37]. There was also variability in types of assays used to measure baseline vitamin D levels among different study populations, varying use of supplementary dosages, calcium co-supplementation, and duration of follow-up ^[42].

However, in light of several favorable study outcomes implicating low vitamin D levels in balance control ^[44], along with basic research to support both a rationale for these findings as well as a linkage to falls risk, and/or recurrent falls ^[34], further studies that take into account possible confounding factors listed in Box 2 may be helpful for arriving at a consensus. Indeed, it is believed that resolving this lack of consensus concerning the clinical significance of any vitamin D-balance association among older people can help to offset any potential confusion for practitioners with regard to vitamin D supplementation ^[40] and is hence an important public health imperative, rather than one solely of scholarly interest.

---

5. Limitations of This Review

This review has some strengths and weaknesses. One weakness is that it does not include peer reviewed articles that are written in languages other than English, or reside in data bases not examined. Another is that there are very few studies with comparable methodological approaches, thus the reasoning in this review is largely descriptive and presented in narrative form. The search strategy was comprehensive, however, and does represent a fair snapshot of the status of this topic and its variable findings and conclusions.

---

6. Conclusion

This literature review revealed over 40 scientific papers related to discussions pertaining to the possible association between vitamin D and balance capacity. Due to the vast variations in these reported approaches, and samples studied, it is impossible to effectively produce a valid systematic meta analytic report. With as many positive as negative study findings, the question driving this present review must be resolved by careful future work that is mindful of the weaknesses in the prevailing literature.

In light of the immense burden of falls among older adults and the current inability of clinicians to recommend the use of vitamin D supplementation as a viable cost-effective falls prevention or supplementary strategy with a high degree of certainty, the provision of more evidence based practice to clarify the subpopulations that are most likely to benefit from treatment in this regard ^[42] is highly recommended. Such data will also help to further our understanding of the determinants of balance as well as falls risk among the elderly.

---

Conflict of Interest

The authors declare no conflict of interest.

---