falls are the leading cause of injury and deaths among older adults worldwide with an estimated 424,000 cases reported each year ( 1 ) . over 30% of those aged over 65 or older and 4050% of those over 80 currently are treated for fall - related injuries ( 2 ) . recurrent falls among older adults have a significant financial , social , psychological , and health - related burden on society , particularly on the health care system . since falls and fall - related injuries result in the loss of over 17 million disability - adjusted life years ( dalys ) , they are considered to be a major public health challenge across the world that calls for global action . in this context , the rapidly increasing number of older adults and the associated risk of fall - related injuries underlines ongoing concerns about the quality of life , costs of care , and demands for support services and preventive programs for vulnerable populations . serum vitamin d insufficiency has been implemented as a major risk factor for osteoporosis , muscle weakness ( 3 ) , falls(2 , 4 ) , fractures(5 , 6 ) and even mortality ( 79 ) . the association between vitamin d insufficiency and the risk of fracture and injuries has been estimated in several studies ( 5 , 6 , 10 , 11 ) . most of the studies have investigated the effect of serum 25-hydroxyvitamin d ( 25(oh)d ) concentration , which is the best indicator of vitamin d status , on bone mineral density ( bmd ) changes ( 6 , 12 , 13 ) . therefore , it has been suggested that vitamin d is a major determinant of bone health . it also has been indicated that low 25(oh)d levelshave been associated with low bmd in older white adults ( 12 , 14 ) . in this regard , further investigations indicated a positive association between serum 25(oh)d and bmd of the hip(5 , 6 , 11)and spine in men . some other studies have suggested that vitamin d has a protective effect on fractures by improving muscle functions and reduced risk of falling ( 24 , 8) . in these studies , low 25(oh)d was found to be associated with poor grip strength , an indicator of muscle strength , balance , and increased risk of mortality in elderly patients . despite its well - documented protective effects , serum 25(oh)d concentration is likely to be one of the most globally - considered contributing factors to bmd changes , muscle strength , fractures , and falls . serum 25(oh)d supplementation has been prescribed repeatedly as a preventive drug for older people , yet there are surprising small number of well - documented randomized , controlled trials measuring its efficacy and potential to reduce the risk of fractures and falls ( 15 ) . prescription of vitamin d supplementation for older people is based on clinical experience rather than well documented , randomized trials that involve an extensive population with different outcomes ( 15 ) . while a great body of the literature suggests vitamin d supplementation as the major contributing factors for reducing the risk of falls and fractures in elderly people , it is unclear whether its efficacy and potential performance leads to better results . therefore , further efforts are needed to investigate the effect of serum 25(oh)d concentration on the risk of falls in older populations . recent data have failed to find any protective effect of 25(oh)d on the risk or rates of falling in older people , yet the association between 25(oh)d concentration level and the risk of falling in older adults has been a topic of heavy debate among healthcare professionals , and , therefore , more investigations are needed to provide evidence of how 25(oh)d status is associated with the risk of recurrent falls . in an attempt to address these challenges , the present study aimed to conduct a preliminary investigation of the association between serum 25(oh)d levels and the risk of recurrent falls in the elderly iranian population . this cohort study was conducted in the emergency departments ( eds ) of rasoul akram and sina hospitals during march 2012january 2013 . a cohort of elderly participants over 60 who suffered from an unintentional episode of falling was evaluated six months after of their first ed visit . of all 120 patients invited to participate in the study exclusion criteria were the use of vitamin d supplements , anti - seizure medications , or glucocorticoids . a structured , self - administered checklist was developed to obtain the participants demographic and clinical information . the questionnaire included demographic information ( age , gender , level of education , marital status ) , past medical history , and serum 25(oh)d concentration of included participants at the time of hospitalization . this checklist was completed during admission and in a six - month of follow up through telephone calls to the patients , their family , or caregivers who were aware of the patients conditions . we also asked about any recurrent fall experience during the six - month follow - up . a valid serum 25(oh)d sample was obtained from all of the patients who participated in the study . non - fasting blood samples were collected from participants during their first visit to the clinic . the serum concentration of 25(oh)d was measured by separating the serum from 5 cm3of clotted blood taken from the participants . the serum 25(oh)d concentration was measured using the enzyme - linked immunosorbent assay ( elisa ) method . data analysis was performed using stata version 12 ( stata corp . , college station , tx ) . descriptive statistics ( mean , median , sd and range ) were used to present the overall characteristics of the participants . spearman s regression coefficient was used to measure the associations between the quantitative variables . in order to compare the mean serum 25(oh)d concentration between different categorical variables , this cohort study was conducted in the emergency departments ( eds ) of rasoul akram and sina hospitals during march 2012january 2013 . a cohort of elderly participants over 60 who suffered from an unintentional episode of falling was evaluated six months after of their first ed visit . of all 120 patients invited to participate in the study exclusion criteria were the use of vitamin d supplements , anti - seizure medications , or glucocorticoids . a structured , self - administered checklist was developed to obtain the participants demographic and clinical information . the questionnaire included demographic information ( age , gender , level of education , marital status ) , past medical history , and serum 25(oh)d concentration of included participants at the time of hospitalization . this checklist was completed during admission and in a six - month of follow up through telephone calls to the patients , their family , or caregivers who were aware of the patients conditions . we also asked about any recurrent fall experience during the six - month follow - up . a valid serum 25(oh)d sample was obtained from all of the patients who participated in the study . non - fasting blood samples were collected from participants during their first visit to the clinic . the serum concentration of 25(oh)d was measured by separating the serum from 5 cm3of clotted blood taken from the participants . the serum 25(oh)d concentration was measured using the enzyme - linked immunosorbent assay ( elisa ) method . data analysis was performed using stata version 12 ( stata corp . , college station , tx ) . descriptive statistics ( mean , median , sd and range ) were used to present the overall characteristics of the participants . spearman s regression coefficient was used to measure the associations between the quantitative variables . in order to compare the mean serum 25(oh)d concentration between different categorical variables , the mean ( sd ) age of the study population was 75 ( 8) . over half of the participants table 1 presents the participants characteristics according to the three levels of serum 25(oh)d studied . the mean ( median ) serum 25(oh)d concentration was 38 ( 34 ) ng / ml . mean serum 25(oh)d levels varied little according to gender groups , men had higher levels of 25(oh)d rather than women ( 39.1 vs. 36.8 , respectively , p=0.450 ) . in addition , mean serum 25(oh)d levels differed between the age groups , ranging from 15.3 ng / ml in those aged over 90 to 43.4 ng / ml in those aged 7180 . according to this finding , an inverse , but insignificant , association was found between the age of participants and their serum 25(oh)d levels ( r=0.03 , p=0.7 ) . table 1 indicates that the mean serum 25(oh)d levels decreased according to bmi categories ( from 42.7 to 33.6 ng / ml , p=0.986 ) . mean serum 25(oh)d level was significantly higher in the group with physical activity of more than 80 min per week ( p=0.03 ) . however , the mean serum 25(oh)d level was found to have no significant association with muscle weakness(p=0.979 ) or dynamic balance scores(p=0.90 ) . figure 1 indicates the distribution of serum 25(oh)d according to recurrent falls and gender categories . according to this figure , besides , the median serum 25(oh)d concentration was decreased insignificantly in line with the increasing number of recurrent falls . however , in women , the median of the serum 25(oh)d concentration followed a different pattern , in which women who experienced recurrent falls had higher scores of serum 25(oh ) than others ( p=0.643 ) . according to these findings , a small but insignificant association was found between the mean serum 25(oh)d level and the number of recurrent falls in elderly patients irrespective of their age , gender , or physical activity groups ( or=1.008 , p=0.992 ) . the mean ( sd ) age of the study population was 75 ( 8) . over half of the participants table 1 presents the participants characteristics according to the three levels of serum 25(oh)d studied . the mean ( median ) serum 25(oh)d concentration was 38 ( 34 ) ng / ml . mean serum 25(oh)d levels varied little according to gender groups , men had higher levels of 25(oh)d rather than women ( 39.1 vs. 36.8 , respectively , p=0.450 ) . in addition , mean serum 25(oh)d levels differed between the age groups , ranging from 15.3 ng / ml in those aged over 90 to 43.4 ng / ml in those aged 7180 . according to this finding , an inverse , but insignificant , association was found between the age of participants and their serum 25(oh)d levels ( r=0.03 , p=0.7 ) . table 1 indicates that the mean serum 25(oh)d levels decreased according to bmi categories ( from 42.7 to 33.6 ng / ml , p=0.986 ) . mean serum 25(oh)d level was significantly higher in the group with physical activity of more than 80 min per week ( p=0.03 ) . however , the mean serum 25(oh)d level was found to have no significant association with muscle weakness(p=0.979 ) or dynamic balance scores(p=0.90 ) . figure 1 indicates the distribution of serum 25(oh)d according to recurrent falls and gender categories . according to this figure , besides , the median serum 25(oh)d concentration was decreased insignificantly in line with the increasing number of recurrent falls . however , in women , the median of the serum 25(oh)d concentration followed a different pattern , in which women who experienced recurrent falls had higher scores of serum 25(oh ) than others ( p=0.643 ) . according to these findings , a small but insignificant association was found between the mean serum 25(oh)d level and the number of recurrent falls in elderly patients irrespective of their age , gender , or physical activity groups ( or=1.008 , p=0.992 ) . in this prospective cohort study of elderly people that were treated in emergency rooms for injuries from falls , no significant association was observed between their serum 25(oh)d concentration and recurrent falls . in addition , mean serum 25(oh)d concentration was not associated with muscle weakness and balance in older adults . in this study , no significant association of 25(oh)d was found with incidence of one or more recurrent falls . in contrast to previous reports , our findings did not support the argument that vitamin d concentration reduces the risk of recurrent falls in elderly people . , the relationship between serum concentration of vitamin d metabolites and falls in older women in the united states was examined , and it was reported that the risk of falling only decreased with high serum 1,25(oh)2d3 concentration , whereas higher 25(oh)d level was not associated with lower risk ( 16 ) . serum 1,25(oh)2d3 concentration was not assessed in participants in our study because of laboratory limitations , but our findings confirmed the second result of this study in that is showed that there was no association between 25(oh ) d levels and falls . in a meta - analysis of randomized controlled trials , the efficacy of the administration of vitamin d and calcium supplements in elderly people to reduce the frequency of falls was examined , but the results found no efficacy ( 10 ) . the findings of previous studies have suggested that low vitamin d status is associated with increased risk of falling and fractures . therefore , vitamin d supplementation has been implemented as a strategy in increasing bmd and reducing the risk of fractures or falls in older people . vitamin d concentration has been suggested repeatedly to be the contributing factor for bmd changes , falls , fractures , and physical performance in older people , but emerging evidence highlights ongoing debates on the protective effect of vitamin d concentration on falls and fractures . while prescribing vitamin d for preventing unfavorable outcomes of bone resorption and turnover is based on clinical practice and cohort studies , there is now evidence that failed to identify any protective effect of vitamin d supplementation on the risk or rate of falling in older people ( both in healthcare facilities or hospitals and in the community ) ( 15 , 17 , 18 ) . our findings also indicated no significant association of 25(oh)d concentration and muscle weakness in older adults . this result was consistent with the findings of a systematic review and meta - analysis that examined the effect of vitamin d concentration on muscle strength in adults ( 19 ) . according to this evidence , vitamin d supplementation showed no significant effect on grip strength , knee flexion strength , or knee extension strength in adults with baseline 25(oh)d > 25 these results provided further evidence that the function , metabolism , and absorption of vitamin d may differ among individuals and even across diverse populations ( 15 ) . however , limited early investigations have suggested an increase in proximal muscle strength in adults with vitamin d deficiency ( 3 ) . in this context , universal recommendations on the use of vitamin d supplementation to improve muscle strength and physical performance of older adults require further evidence . first , the design of our study did not allow us to investigate the causality effect of vitamin d and recurrent falls . also , we did not consider important covariates , including body mass index , education , smoking , use of alcohol , and health status when we analyzed the potential associations between serum vitamin d concentration and recurrent falls in older people . in addition , a single baseline measurement of serum vitamin d , was used to categorize the participants , and this could have led to misclassification of the participants , because single baseline measurements may not have reflected their long - term biochemical status . we excluded those subjects who took vitamin d supplements during the six - month follow - up . the efficacy of vitamin d supplements in reducing recurrent falls was not investigated in our study . despite these limitations first , this is the first population - based study to examine the incidence of recurrent fractures with serum vitamin d concentration in the iranian population . therefore , these findings provide further evidence of the effect of vitamin d on recurrent falls in people with diverse ethnic backgrounds . second , this study used direct serum measures of vitamin d instead of other indirect measures , including questionnaire - based scales or food frequency intakes of vitamin d - rich foods . in summary , our study findings failed to support the argument that vitamin d concentration is associated with the reduced risk of falling in older adults . no significant association of vitamin d was found with incidence of recurrent falls , muscle activity , and balance . the association between vitamin d insufficiency and the risk of fracture and injuries has been investigated repeatedly , but the results remain controversial across different populations . therefore , this study aimed to investigate the protective role of vitamin d concentration against falls in the elderly iranian population . by using serum vitamin d concentration as a direct measure of vitamin d , this study failed to support the argument that vitamin d concentration is associated with the reduced risk of falling in older adults . according to our findings , no significant association was observed between serum vitamin d concentration and recurrent falls , muscle activity , and balance . our findings provided further evidence that the function , metabolism , and absorption of vitamin d may differ among individuals and even across diverse populations . yet , the results are still incomplete , and further trials are needed to reach conclusive decisions .
introductionserum vitamin d concentration is a major contributing factor for increasing the risk of fall and fall - related injuries in older adults . however , 
 when prescribed and supplemented for these populations , the outcomes are controversial , and in several cases no improvement has been reported in reducing the risk of recurrent falls . 
 this study aimed to examine the association between serum vitamin d concentration and recurrent falls in iranian older adults.methodsthis cohort study was conducted in the emergency departments of two university hospitals . 
 a cohort of 82 elderly participants aged over 60 and suffered from an unintentional episode of falling was evaluated six months after their first ed visit . 
 a structured , self - administered checklist was developed to obtain the participants demographic and clinical information . 
 participants also were asked about any recurrent fall experience during follow-up.resultsthe mean ( sd ) age of the study population was 75 ( 8) . 
 over half of the participants were male ( 57.3% ) . 
 the mean ( median ) serum 25-hydroxyvitamin d ( 25 ( oh)d ) concentration was 38 ( 34 ) ng / ml . mean serum 25(oh)d levels varied slightly between gender groups ( p=0.450 ) . 
 an inverse but insignificant association was found between the age of participants and their serum 25(oh)d levels ( r=0.03 , p=0.7 ) . 
 a small but insignificant association also was found between the mean serum 25(oh)d level and the number of recurrent falls in elderly patients irrespective of their age , gender , or physical activity groups ( or=1.008 , p=0.992).conclusionin contrast to previous studies , no significant association of serum 25(oh)d concentration was found with recurrent falls in iranian older adults .