In terms of controlled or prospective studies that have examined vitamin D and balance associations, Dukas et al. 22 who studied 237 participants, mean age 75.9 years who received daily vitamin D treatments found the supplementary treatment was accompanied by a significantly increased balance capacity at three 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. It was concluded that the supplementary treatment with alfacalcidol containing vitamin D3 was effective in improving muscle strength, and balance, and in reducing falls numbers and rates.

Bogaerts et al. 43 who compared the effect of a regular dosage versus a higher dosage of daily vitamin D 3 (880 IU vs 1600 IU) versus exercise to improve balance among 113 older institutionalized individuals randomized to a vibration exercise group or control group found dosage rates of vitamin D did not impact their measures of balance and gait differentially. Studying only healthy adults, average age 79.6 years, this group measured the subjects dynamic balance along with their falls risk before and after six months. Results showed no differences in any outcome were predicted by the vitamin D dosages, and that there were also no differences in falls risk, regardless of exercise status, nor any postural control differences. These results by Bogaerts et al. 43 were however, not consistent with those of Annweiler et al. 28 where higher serum vitamin D concentrations were associated with better balance among older adults categorized as having supra-optimal vitamin D status. They did align however with those of Bird et al. 32 who found no association between seasonal vitamin D variations and postural sway measures in independently mobile older adults assessed prospectively.

The findings in the literature may however, depend on what is measured. For example, in a study by Iwamoto and Saito 26 designed to clarify the effect of a vitamin D derivative on body balance, these authors found no significant improvement in the unipedal 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, unipedal 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. 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.

To add to the confusion, a two year follow up study by Uusi-Rasi et al. 44 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. 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, but only exercise improved muscle strength and balance. While vitamin D had no mediating exercise effect on physical functioning, those using vitamin D without exercise or exercise alone, showed evidence of lower Hazard ratios for fall injuries. However, the accuracy of monthly falls diary reports, the definition of falls applied, the nature of the balance measures, the method of classifying and analyzing falls incidents, baseline serum levels all above 26 nm/ml, and the exclusion of non-injurious falls in the analysis may have influenced the outcomes observed.

As argued by Anek et al. 45, the impact of vitamin D supplementation may not only depend on what is measured in clinical trials, but may well depend on the extent of the vitamin D dosage or its mode of delivery or both among a multitude of other factors, such as type of vitamin D analog applied. For example, despite some negative findings between balance and vitamin D correlates when vitamin D3 supplementary dosages prevail 44, Anek et al. 45 showed that high supplementary doses of vitamin D2 ^{as opposed to D3} did yield improvements in balance ability at the post test conducted on normal stability surfaces when experimental subjects were compared with a control group. 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. It was concluded that a short-term vitamin D2 supplementation period may reduce the falls risk that prevails among older women.

Similarly in a study by Cangussu et al. 46 the authors who applied vitamin D supplementation to postmenopausal women fallers found falls rates were almost 50% higher in the control group, and 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, indicating a positive independent outcome of D supplementation on postural balance after 9 months, along with a significant falls reduction rate. Cangussa et al. 46 who conducted one of the very few studies that have been designed specifically to evaluate the impact of isolated vitamin D supplementation on falls rates and postural balance among older women fallers using a double-blind, placebo controlled trial design found reductions in both these factors at 9 months. Moreover, the mean vitamin D values over the 9 months increased in the experimental, but not the control groups where they declined and where there were proportionately more falls as deduced through interviews. As well, balance parameters improved only in the supplemented group. Studied were 160 postmenopausal women, ages 50-65 years, with a history of at least one fall in the past 12 months of which 80 received vitamin D3 supplementation of 1,000 IU/day administered orally for nine months. The researchers omitted adults with neurological or musculoskeletal disorders, balance disorders, drugs that could affect balance and those with osteoporosis. The subjects' postural balance was assessed using computerized stabilometry, serum vitamin D was assessed by high performance liquid chromatography, and the numbers of falls incidents were recorded by interviews.

The application of vitamin D to increase a vulnerable older subjects serum levels, as well as potentially impacting fall risk favorably 47, has however, been disputed quite recently as far as its possible influence on musculoskeletal health, including falls prevention by Bolland et al. 48 and Smith et al 49. Vitamin D therapy, may also fail to prevent falls and fractures if delivered in the form of 500,000 IU of oral vitamin D ingested annually to avert declines in vitamin D exposure during the autumn and winter months in older adults who are mostly not vitamin D deficient 50. However, Hillstrom et al. 51 who recently reported on pilot work that attempted to determine if attaining higher than recommended vitamin D levels of > 20 ng/ml believed to foster overall health, plus bone health, and balance would in fact do so, generally found vitamin D to impact favorably on muscle function, balance, and overall muscle size of post menopausal women. Similarly Sahin Alek et al. 52 who strove to verify that vitamin D is not only associated with calcium homeostasis, but skeletal muscle health and some chronic diseases found that vitamin D replacement administered especially to their most deficient cases tended to improve their elderly subject s balance.

Levis and Gomez-Marin 53 however, found no added benefit in this regard post vitamin D supplementation of 4000IU per day for 9 months, nor in regards falls risk among older sedentary men m/ml) ages 65-90 with low vitamin D baseline levels [< 30 nm/ml] in a randomized, double-blinded controlled trial of 130 men. Although vitamin D levels increased markedly, gait and balance did not improve in the experimental group compared to the control group.

In other research involving 68 sarcopenic patients, an 8-week intervention of branched-chain amino acids and vitamin D supplementation with low-intensity resistance training did indeed improve muscle-related outcomes in these older adults 54. Analagous data from Smimeca et al. 55 recently showed that there is a possible clinically relevant relationship between sarcopenia (evaluated in term of fibers atrophy), vitamin D receptor protein expression and TaqI/Cdx2/FokI VDR genotypes in an Italian cohort of older adults with either osteoporosis or osteoarthritis. These data implied that vitamin D sufficiency or its attainment may yet have an indirect bearing on the relationship between sarcopenia measures, vitamin D receptor protein expression and TaqI/Cdx2/FokI VDR genotype measures, and hence on the extent to which balance control impacts falls risk.

Other data have shown that intra muscular vitamin D applications, which are not well studied, can indeed have a marked effect on balance in vitamin D deficient elderly women 56, while more recently, Susuki et al. 57 who evaluated the effects of anti-osteoporosis agents, eldecalcitol, an analog of vitamin D and alendronate, a drug for treating osteoporosis on dynamic and static postural balance in aged patients with osteoporosis in a randomized, open-label, controlled clinical trial of 124 female patients aged 65 or over with osteoporosis found the vitamin D analog to produce favorable results after 24 weeks. The primary endpoint assessed was the change in a postural balance index, adjusted composite equilibrium score of sensory organization test, wherein there was no statistically significant dynamic balance improvements that were noted over time between the two groups, static postural balance was maintained in the vitamin D group, but not in the alendronate group.

In sum, despite efforts to control for extraneous factors, and to undertake follow up studies, on an array of samples, not all researchers concur that there is an association between balance and vitamin D status in older adults that can be mobilized to explain falls risk as well as mobilized to consistently prevent or reduce falls risk (see Table 2).

As outlined in additional clinical studies related to the present topic, vitamin D supplementation may be expected to have a bearing on balance capacity by improving corticospinal neural transmission 60, gait control 21, cognitive function 61 and healing post surgery 6263. As well, recent data show all analyzed human brain regions to contain some level of vitamin D 64, and implying that vitamin D appears to have a bearing on the speed of intracranial processing and cerebellar volume 6566. Vertigo that could impact falls risk negatively due to its possible destabilizing effects may be also be influenced by the prevailing level of vitamin D 67. Other data show vitamin D supplementation can enhance both physical and cognitive health 59, muscle function 222369, muscle strength, 2425, muscle mass, power and contractile capacity 686970, navigational and cognitive performance 2771, postural control 72 postural adaptations 28, and lower extremity function in the elderly 687374. Falls prevention itself also continues to be demonstrated in cases that receive daily vitamin D supplementation 75 as well as bone, muscle, and nerve health 76.

Low vitamin D levels, in contrast, tend to be linked to muscle mass, strength and contractile capacity declines, poor muscle endurance capacity 7778 plus suboptimal physical performance ability 68. The accuracy of motor imagery during gait 59 is also found to be reduced in the presence of insufficient serum vitamin D levels.

Withdrawal of psychoactive drugs

Depression identification and treatment

Vision interventions

Environmental assessments and modifications 848586

In this regard, and for almost two decades, the recommendation that optimal levels of vitamin D be employed as one of the multiple efforts advocated to prevent falls injuries among older adults has been discussed favorably by some 758788, and mentioned by others ^{eg 4}685. However, even though vitamin D supplementation, is emerging, as a potentially safe and well-tolerated falls prevention strategy due to its potential beneficial effects on the musculoskeletal system along with anticipated improvements in muscle strength, balance and navigational abilities 86 when applied to achieve adequate serum levels 87, the question of whether vitamin D can impact muscle-associated falls injury risk favorably in older populations or does not affect falls risk in any way 48 remains in question 89. The negative studies that prevail in this regard ^{eg 90} are also contrary to recommendations for the supplementation of vitamin D where indicated to maintain musculoskeletal health in older adults 91, especially those with low vitamin D levels 92 and in the context of falls prevention efforts among the elderly 78939495. This also includes overall health status, as well as muscle endurance, muscle mass and strength, bone mineralization 95, and neuropsychological functional benefits 37. Yet, despite being quite well grounded in a fairly strong rationale and set of contemporary studies 4252819495, not all authors concur. Indeed, as outlined in Table 1 and Table 2, even though negative or null findings are often not published, there are several non-supportive and basically unanticipated adverse findings in this regard in both the recent and past literature concerning vitamin D and balance and falls risk correlates in the elderly 96. At the same time, as implied in other falls vitamin D reports 7588 some of these observed differences clearly implicate the variations in the nature of the study sample, possible gender issues, the study duration, design and its quality, nutritional status 97, vitamin D dosages 3749, and outcomes assessed. As well, flaws in available studies, especially the aggregation of diverse input and output variables, and the limited power to demonstrate effects that exist may be leading to these competing conclusions 98. Moreover, the impact of medical status, vision, sleep factors, dietary factors, food intake, nutrition and falls education, and other co-intervention effects, plus variations in initial vitamin D status and vitamin D supplementation adherence rates, is often hard to tease out in studies examining falls injury risk, vitamin D and balance attributes. As well the confounding role of falls history, fear of falling, frailty, type of vitamin D analog used, genetic influences of vitamin D receptors on muscles in sarcopenic adults 99, plus mode of vitamin D administration remains relatively understudied 98. According to Thanapleutiwong et al. 75 the results of a prior negative meta-analysis by Bolland et al. 48 may have been due to its focus on vitamin D monotherapy rather than including studies employing vitamin D analogues, plus studies which compared vitamin D plus calcium and placebo.

Moreover, how balance is defined and measured is not standardized in any way between studies, and may include measures of perceived subjective balance perceptions, postural perturbation tests, and static balance tests often conducted indoors that may not emulate those protective responses occurring or needed in actual fall situations. Similarly, how vitamin D intake is assessed may be questionable, as may serum measures of vitamin D over differing seasons, or fluctuations in health states At the same time, balance associated assessments using the sit-to-stand timed tests are often employed differentially, sometimes representing balance capacity, at other times representing muscle power. It is also challenging to account for how vitamin D found to improve vitamin D levels in fallers with vitamin D insufficiency, is observed by some to produce more injurious results than not 4849100, for example Thanapleutiwong et al. 75 implies this might be linked to non-adherence to daily vitamin D supplementation, rather than excess vitamin D intake, but this has not been well studied. At the same time, Burt et al. 101 found no differences in balance control effects after three years, between participants who took either high, medium or low supplementary doses of vitamin D Limitations that have been discussed as explanations for the diverse study findings in the present context, include the use of control groups that are actually receiving vitamin D₃ overtly or inadvertently, per day, rather than a placebo. As well, dose findings may end before the pre-specified thresholds for dose suspension and dose selection are reached 90. High dose application studies also require careful investigation ^{eg 100} to rule out other factors for their generally discordant results. As well, the optimal approach for helping to raise vitamin D serum levels in deficient cases in the older adult population to an optimally beneficial vitamin D level has not been thoroughly examined. Similarly, other possible confounding impacts of prevailing studies that merit study are the role of outdoor vitamin D exposure, food based vitamin D components, supplements that already contain vitamin D, plus prevailing health and medication status.

In the meantime, and in light of several study outcomes implicating low vitamin D levels in balance control 424452, along with basic research to support both a rationale for validating these findings as well as a linkage to falls risk 94104, and/or recurrent falls 34, it is hard to accept the idea that vitamin D administered on an individualized basis 102 should be withheld from older adults who are clearly vitamin D deficient and at high risk for falling. Even if falls are not impacted, health status as well as muscular status may in fact at the very least be potentially improved 3495. Moreover, given the ongoing COVID-19 pandemic and associated health care restrictions, and the fact that fallers who enter the hospital are at high risk for COVID-19 infection, more protective care in this regard appears imperative.

At the same time, researchers who desire to advance this line of research in a meaningful way might consider more careful subgroup analyses along with carefully designed single case studies, case reports, basic laboratory studies, and larger well powered clinical studies that employ more universal agreed upon standardized vitamin D classifications, clear understandings of what constitutes a fall, and balance associated measures that can serve as a proxy for falls risk. The use of more universally agreed upon objective outcome assessment procedures in studies of both short-term as well as of longer duration and that employ more sophisticated technologies to measure falls over time 102, rather than relying on interviews and surveys are strongly encouraged. As per findings of Bischoff Ferrari et al. 103, and in light of current fiscal as well as other health services constraints, dedicated efforts to define what constitutes safe efficacious vitamin D supplementation as well as unsafe levels are also highly desirable. Delineating the role of age, gender, health status, falls history, and environmental factors in this regard is also paramount and may not only greatly help to allay considerable human suffering, but the potentially highly negative consequences of referral to hospitals during COVID-19 due to falls, which seem to have increased in frequency and poor outcomes during the pandemic, rather than decreased 105.