INTRODUCTION
Older adults with type 2 diabetes mellitus (T2DM) are at risk of experiencing disease-associated complications such as cognitive impairment and falls.1,2 Falls negatively impact overall quality of life, as they often lead to declines in mobility, avoidance of activities, and institutionalization. In older adults, diabetes is an independent risk factor for falls with risk differing based on disease management, as those with poor glycemic control who require insulin have a higher fall risk and incidence than those who are non–insulin-dependent.3,4 Fall risk is further complicated by the presence of cognitive impairment in older adults, as those with impaired cognition fall more often than their cognitively intact peers.5
Older adults with diabetes are twice as likely to develop Alzheimer disease or vascular dementia as compared with age-matched peers.1,3,6–8 The increased incidence of cognitive impairment in those with diabetes is believed to be attributed to accelerated brain aging, which is often associated with and confounded by insulin dysregulation.9,10 Structural changes within the brain in those with diabetes include the presence of white matter lesions, subcortical and cortical ischemic changes, and general atrophy within the brain that present clinically as impaired memory (eg, recall), orientation, processing speed, and executive function.11 Declines in the cognitive domains of recall and executive function result in overall poor management of T2DM and associated sequelae. In addition, mismanagement of blood glucose levels in the way of hypoglycemia increases the risk of cognitive dysfunction, confusion, dizziness, and poor coordination and contributes to falls and fall-related injuries in this population.9,10
Beyond the risk factors associated with the presence of cognitive impairment or impaired glycemic control, the problem of falls in older adults with T2DM is further confounded, as fall risk is multifactorial and includes both internal and external risk factors.8 An accelerated loss of lower extremity muscle strength in the form of sarcopenia, along with decreased skeletal muscle mass, has been reported in those with T2DM that contributes to increased frailty and falls.12 This loss of strength likely influences physical activity levels, as older adults with diabetes are twice as likely to be unable to walk a quarter of a mile, climb stairs, or complete housework as compared with those without diabetes.13 Changes in gait that contribute to falls have also been identified in this population, and they include decreased gait speed, a wider base of support, shortened step length, and increased double stance time.14 Finally, the presence of distal sensory impairments in the form of peripheral neuropathy, vestibular dysfunction, and visual impairment also contribute to falls.15–17 A number of studies have examined these fall risk factors in older adults with T2DM, but a gap in the literature exists describing the specific cognitive processes that contribute to falls in this population.
A growing body of evidence supports associations between cognitive impairment and falls,6 with a greater emphasis more recently on identifying and then addressing the roles that specific cognitive processes, such as executive function, play in falls.18 Declines in the cognitive domains of recall, executive function, orientation, and processing speed have been reported in those with diabetes in cross-sectional studies, with greater cognitive impairment reported over time.19 However, the cognitive domains that influence falls in older adults with T2DM are currently unknown. Therefore, the aim of this study was to first describe the impact of cognitive function on falls in older adults with T2DM. Then, because cognition has been reported to become more impaired with advanced age and falls more prevalent, a second aim was to describe the contributions of cognition on fall incidence by age group, comparing a younger and older group of adults older than 65 years with T2DM.
METHODS
A cross-sectional analysis was completed using data from the 2010 wave of the Health and Retirement Study (HRS). The HRS is a prospective longitudinal study sponsored by the National Institute on Aging and completed by the University of Michigan Institute for Social Research.20 Every 2 years, the HRS surveys a representative sample of approximately 20 000 community-dwelling people 50 years or older in the United States and includes economic, social, cognitive, and health-related data.20 A detailed description of the HRS and study data sets can be accessed at http://hrsonline.isr.umich.edu.20 This study was approved through the institutional review board of the University of Michigan–Flint. All respondents provided informed consent, and their anonymity was preserved in the process.
The baseline interview took place between February 2010 and November 2011 and comprised 22 034 individuals whose information was provided by the respondent or their proxy. HRS respondent data were included if respondents were older than 65 years, had a self-reported diagnosis of diabetes after the age of 40 years, and did not have Alzheimer disease, dementia, or a history of stroke. From the sample, respondents who had incomplete demographic, disease, or cognitive information were excluded. This resulted in a total sample of 1171 older adults with T2DM.
Demographic data extracted from the data set included age (years), marital status, gender, and education. Diabetes-related variables included the time (years) since diagnosis, use of oral medications or insulin for diabetes, and the presence of kidney disease from diabetes. Other health-related variables included the reported frequency of engaging in mild, moderate, or vigorous physical activity at least once per week and anthropometric measures for calculation of body mass index (BMI) in kg/m2. Fall data extracted included fall incidence, number of falls, and injury from the fall (yes/no). Incidence was reported when asked whether the respondent had fallen in the 2 years prior to the survey. If the respondent had fallen, he or she was asked to recall the total number of falls as well as whether an injury had occurred from the fall.
Physical performance data extracted from the 2010 wave of the HRS data set included gait speed, strength, and balance data. Gait speed was measured over 2 trials, and the time in seconds needed to cover an 8-foot distance was recorded, which was then converted to meters per second for analyses. Grip strength measurement with a handheld dynamometer was performed as a general measure of overall strength. Respondents were asked to identify their hand dominance and then 2 measures of grip strength were performed for each hand, alternating between measurement trials. The average of the measures (in kilograms) was recorded for each hand. Tandem balance was assessed by recording the amount of time (in seconds) respondents were able to stand in a full tandem position. Respondents were required to hold the full tandem position for 30 seconds. The total amount of time to hold tandem stance was recorded.
Cognitive data extracted from the same 2010 wave of the HRS data set included assessments of memory (immediate [IWR] and delayed word recall [DWR]), orientation, and executive function, of which each of these has been reported to decline over time in adults with diabetes.11,19 Immediate word recall was tested by the interviewer by having the respondent recall as many words as possible in any order from a randomly assigned list of 10 nouns immediately after they were read by the interviewer. Then, after a period of 5 minutes had passed and during which the respondent was engaged in other tasks, DWR was tested which required respondents to name as many of those original 10 words. For both recall measures, the number of correctly recalled words was recorded as the total score. Orientation was assessed by the respondent being able to accurately give the correct day of the week, month, day, and year, with a total score possible of 4 for this measure. Executive function was assessed using a semantic verbal fluency test that required respondents to name as many animals as one could in 60 seconds, with the total number of named animals to comprise the score. The verbal fluency task requires the use of strategic search, set-shifting, and semantic memory and is considered a measure of executive function.21
Although age has been reported to influence both cognition and falls,4,22 the sample was split on the basis of the mean age of the sample creating a younger group (age 65-74 years) and older group (age 75+ years). All respondent characteristics were first described in the whole sample and then for each group. Characteristics were compared by group assignment using analysis of variance for continuous variables and χ2 for categorical variables. Logistic regression analyses were performed to examine associations between cognitive function and falls, initially for the full sample and then for each group. The cognitive predictor variables included executive function, IWR, DWR, and orientation. The outcome variable was falls (yes/no, coded as 1 or 0) within 2 years prior. Covariates controlled for in regression models were those that were significantly different between groups and included age, time since diabetes diagnoses, marital status, BMI, grip strength, gait speed, and physical activity (mild intensity). All data were analyzed using Statistical Package for the Social Sciences (SPSS) version 24 (IBM Corp, Armonk, New York), and a significance level was set at P < .05.
RESULTS
Overall, 1171 individuals met inclusion criteria and comprised the study population. The mean age was 74.3 years (SD = 6.1), 62% were married, 50.7% were female, and, on average, 10.8 years (SD = 6.9) had passed since the diagnosis of diabetes. Falls were reported by 37.5% of respondents, with an average of 2.9 falls (SD = 3.0) reported per participant with a history of falls and of which 28.5% were injurious falls. Average physical mobility variables included a mean gait speed of 0.73 m/s (SD = 0.22) and tandem stance time of 21.1 seconds (SD = 11.0) out of a total of 30 seconds. Mean scores on the cognitive measures included 5.3 (SD = 1.5) words and 4.3 (SD = 1.7) words for immediate and delayed recall measures, respectively, an orientation score of 3.8 (SD = 0.5), and 15.6 (SD = 5.9) animals named for the semantic verbal fluency executive function measure.
Within the sample, 43% (N =509) were 75 years or older and were assigned to the older group whereas the other 662 were assigned to the younger group. Significant differences between groups existed across multiple demographic variables including age, years since diabetes diagnosis, marital status, BMI, oral medications for diabetes management, and physical activity. Education was not different between groups, nor was the use of insulin for disease management. On average, those in the older group had a lower grip strength, walked slower, and were not able to hold a tandem stance position as long as those in the younger group, as each of these variables were statistically different between groups. Fall incidence differed between groups, with 44.3% of the older group members reporting a fall in the 2 years prior to the survey versus 32.3% of the younger group. However, the average number of falls and injuries from falling did not differ between groups.
Cognitive function was significantly different between groups on all measures. Recall was more impaired in the older group for both IWR (4.8 words, SD = 1.6) and DWR (3.9 words, SD = 1.6) tasks than in the younger group (IWR = 5.6, SD = 1.4; DWR = 4.7, SD =1.7). Executive function as measured with the semantic verbal fluency test was more impaired in the older group (14.8 animals named, SD = 5.5) than in the younger group (16.4, SD = 6.2). Orientation to the day of the week, month, day, and year differed by group, with those in the older group with lower mean scores of 3.7 (SD = 0.5) for this measure. Full demographic, mobility, and cognitive variable information can be found in Table 1.
Table 1. -
Demographic, Mobility, and Cognitive Data of the Sample and by Group Assignment
| Variable |
Total Sample (N = 1171) |
Younger Group (n = 662) |
Older Group (n = 509) |
P
|
| Mean (SD) or % |
Range |
Mean (SD) or % |
Range |
Mean (SD) or % |
Range |
| Age, y |
74.3 (6.1) |
65-97 |
70.0 (2.8) |
65-74 |
80.0 (4.4) |
75-97 |
.00a |
| Years since diabetes diagnosis |
10.8 (6.9) |
2-43 |
10.1 (6.3) |
2-32 |
11.7 (7.7) |
2-43 |
.00a |
| Gender, % female |
50.7 |
... |
52.4 |
... |
48.5 |
... |
.19b |
| Marital status, % married |
62 |
... |
67 |
... |
55 |
... |
.00b |
| Education, y |
12.8 (2.8) |
1-17 |
12.8 (2.8) |
1-17 |
12.7 (2.8) |
1-17 |
.52a |
| Oral diabetes medication, % |
78.8 |
... |
80.7 |
... |
76.3 |
... |
.03b |
| Taking insulin, % |
7.9 |
... |
9.9 |
... |
5.3 |
... |
.57b |
| Kidney disease, % |
10.0 |
... |
10.7 |
... |
9.2 |
... |
.43b |
| Fallen in previous 2 y, % |
37.5 |
... |
32.3 |
... |
44.3 |
... |
.00b |
| Number of falls |
2.9 (3.0) |
1-30 |
2.9 (3.2) |
1-30 |
2.9 (2.8) |
1-20 |
.79a |
| Injury due to fall, % |
28.5 |
... |
27.7 |
... |
29.3 |
... |
.71b |
| Body mass index, kg/m2
|
32.2 (5.8) |
17.3-52.5 |
33.3 (5.8) |
17.3-49.6 |
31.0 (5.5) |
19.0-52.5 |
.00a |
| Grip strength, kg |
28.4 (9.9) |
0-57.5 |
29.6 (10.1) |
0-57.5 |
26.9 (9.5) |
5.0-52.3 |
.00a |
| Gait speed, m/s |
0.7 (0.2) |
0.2-1.4 |
0.8 (0.2) |
0.3-1.4 |
0.7 (0.2) |
0.2-1.4 |
.00a |
| Tandem stance time, s |
21.1 (11.0) |
0-30 |
21.2 (10.6) |
0-30 |
21.1 (11.3) |
0.1-30 |
.88a |
| Immediate word recall |
5.3 (1.5) |
1-10 |
5.6 (1.4) |
2-10 |
4.8 (1.6) |
1-10 |
.00a |
| Delayed word recall |
4.3 (1.7) |
0-10 |
4.7 (1.7) |
1-10 |
3.9 (1.6) |
1-10 |
.00a |
| Orientation |
3.8 (0.5) |
0-4 |
3.8 (0.4) |
1-4 |
3.7 (0.5) |
1-4 |
.00a |
| Executive function |
15.7 (5.9) |
2-46 |
16.4 (6.2) |
2-46 |
14.8 (5.5) |
4-35 |
.03a |
| Physical activity at least once a week, % |
| Mild intensity |
31.2 |
... |
29.9 |
... |
32.9 |
... |
.00a |
| Moderate intensity |
16.8 |
... |
17.4 |
... |
16.1 |
... |
.03a |
| Vigorous intensity |
6.7 |
... |
7.4 |
... |
5.9 |
... |
.04a |
aAnalysis of variance.
bChi-square test.
Associations between cognition and falls from logistic regression analyses of the whole sample revealed that executive function was associated with fall incidence (odds ratio [OR] = 1.06; 95% CI, 1.02-1.09; P < .05). None of the other cognitive predictor variables were significantly associated with falls after controlling for age, years since diabetes diagnosis, marital status, BMI, strength, gait speed, and physical activity.
When associations between cognition and falls were considered relative to group assignment, the relationships differed. In the younger group, executive function was the only significant predictor of falls (OR = 1.06; 95% CI, 1.01-1.11; P < .05) and of which the association was similar to those found in the full sample. Recall and orientation were not significant predictors of falls in the younger group. Executive function was also a significant predictor of falls in the older group (OR = 1.07; 95% CI, 1.01-1.13, P < .05). However, delayed recall was a stronger predictor of falls (OR = 1.28; 95% CI, 1.03-1.59; P < .05) in this group. In those older than 75 years with T2DM, results indicated that neither immediate recall nor orientation was a significant predictor of falls. Regression results can be found in Table 2.
Table 2. -
Cognitive Predictors of Falls in Older Adults With Type 2 Diabetes in the Whole Sample and by Group Assignment
a
| Cognitive Variable |
Total Sample (N = 1171) |
Younger Group (Age 65-74 y) (n = 662) |
Older Group (Age 75+ y) (n = 509) |
| Odds Ratio |
95% CI |
P
|
Odds Ratio |
95% CI |
P
|
Odds Ratio |
95% CI |
P
|
| Immediate recall |
1.1 |
1.0-1.3 |
.11 |
1.2 |
0.9-1.5 |
.17 |
1.1 |
0.9-1.4 |
.24 |
| Delayed recall |
1.2 |
1.0-1.3 |
.06 |
1.1 |
0.9-1.3 |
.47 |
1.3 |
1.0-1.6 |
.03 |
| Orientation |
1.2 |
0.8-1.8 |
.48 |
1.1 |
0.6-2.1 |
.73 |
1.3 |
0.7-2.4 |
.50 |
| Executive function |
1.1 |
1.0-1.1 |
.00 |
1.1 |
1.0-1.1 |
.02 |
1.1 |
1.0-1.1 |
.02 |
Abbreviation: CI, confidence interval.
aAdjusted for age, years since diabetes diagnosis, marital status, body mass index, and physical activity.
DISCUSSION
This study describes relationships between cognitive function and falls in a national sample of older adults with T2DM. Using simple cognitive screening measures, delayed recall and executive function were found to be significant predictors of falls. Because cognitive function as well as physical function differed between groups with more impairment in those older than 75 years, both cognitive and physical functions should be measured when completing a fall risk assessment in older adults with T2DM.
A greater percentage of falls were reported in the older group (44.3%); however, the number of falls did not differ between groups. Previous research has reported that fall risk increases with age in diabetes and with disease management, with a 94% greater risk for falling in insulin-treated older adults with diabetes.4 In both groups, less than 10% reported using insulin despite having diabetes for an average of 10.8 (SD = 6.9) years, indicating that the sample population may have a lesser severity of disease with better glycemic control and thus limit the generalizability of the results. Future study is needed to examine the role of cognitive function on falls in insulin-treated older adults with diabetes.
Decreased gait speed is associated with impaired cognition and a greater fall risk in community-dwelling older adults.22–26 General gait changes reported in those with diabetes include a slowed speed, decreased stride length, and a wider base of support.14 As compared with the younger group, in the older group, gait speed was slower, a greater percentage of falls were reported, and cognition was more impaired across all 4 measures. These findings would suggest that cognitive function may influence not only falls but also gait in older adults with T2DM, specifically in those older than 75 years; however, further research is needed.
This is the first study to recognize delayed recall as a significant predictor of falls in adults older than 75 years with T2DM. Delayed recall has been reported to be more impaired in older adults with diabetes than in those without the disease.19 Impaired recall contributes to poor disease management and when present with a slowed gait, mortality risk increases.27 Given that delayed recall contributes to diabetes management and that fall risk increases when DWR is impaired, clinicians should consider screening delayed recall when determining fall risk, specifically in those older than 75 years.
Declines in executive function are associated with falls in older adults after controlling for age, sex, health status, education, and a history of falls.22 Executive function was consistently associated with falls across the whole sample and within both groups; however, ORs in this study were much lower than what has been previously reported in community-dwelling older adults.28,29 Differences in ratios may be accounted for by the measures used, as a more comprehensive measure of executive function was used compared with the verbal fluency test.28 Nevertheless, assessing executive function is necessary, as impaired executive processes contribute to poor performance on dual-task gait activities and also result in more pronounced changes in gait such as slowed walking speeds and a longer stance time in diabetes.30 Furthermore, impaired executive function has been reported to influence mismanagement of blood glucose levels and contribute to falls and fall-related injuries.10 Despite the low OR, the importance of screening executive function as a part of a fall risk assessment cannot be dismissed. Nevertheless, more studies should be conducted with other measures of executive function to expand upon these findings.
Orientation is one of the most commonly performed cognitive screens within a fall risk assessment.31 In this study, orientation was not associated with falls in older adults with diabetes within the total sample or when considered relative to age group after adjusting for multiple covariates. Given that there is a paucity of literature describing relationships between orientation assessments and fall incidence, these findings suggest that orientation should not be the only cognitive screening measure used. Other cognitive measures should be considered that have been suggested for use in older adults with T2DM such as the Mini-Cog, which is a screening tool for cognitive impairment,32 or the Montreal Cognitive Assessment tool, which is a screening tool for mild cognitive impairment,30 in order to gather additional cognitive data that have been associated with falls and falls-associated mobility.
Strengths of the study include using a national sample of older adults with T2DM and the use of simple cognitive and physical mobility screening measures that can be easily implemented in clinical settings. However, limitations to the study should be considered. First, respondent or proxy data regarding having a diagnosis of T2DM were gathered as a “yes/no” response and verification of medical history was not performed. In addition, the sample included only those who were diagnosed with diabetes after the age of 40 years to limit analyses to those with T2DM; however, the question asked by the HRS interviewer may have been misinterpreted and some may have had diabetes insipidus instead. Just one measure for each of the cognitive domains was used, and other more comprehensive measures should be considered when examining cognitive function and falls in those with T2DM. The use of a large data set for a secondary analysis allows for the comparison of different variables, but problems with missing data and inaccurate data provided by proxy respondents may result in inaccurate responses. Impaired recall data regarding the diagnosis of dementia or other components of their social or medical history (such as falls) may not be accurate. Therefore, the results of this study of the relationship between cognitive function and falls in older adults with T2DM should be used conservatively. The presence of other factors that contribute to falls in those with diabetes, such as sensory impairments, was not assessed and therefore not controlled for in regression analyses. Finally, this was a cross-sectional study that prevents determining the causality relationship between cognitive performance and falls in older adults with T2DM.
CONCLUSIONS
A growing body of literature has indicated that cognitive function plays a role in falls and that specific cognitive functions contribute to falls differently or more often than others. This study extends that literature to include older adults with T2DM in whom cognitive function is associated with falls after controlling for demographic and physical mobility- and strength-related variables. At a minimum, clinicians should screen executive function and both executive function and recall in those older than 75 years when assessing fall risk in older adults with T2DM.
ACKNOWLEDGMENTS
The author thank the older adult respondents of the HRS 2010 wave and Mary Guyette for assistance with the literature review for the manuscript.
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