Developing Mobility Disability Research Articles

COGNITIVE RESERVE AND RISK OF MOBILITY DISABILITY IN OLDER ADULTS

Abstract Background Cognitive Reserve (CR) protects against cognitive decline and dementia but its relation to mobility disability has not been established. To address this important gap in the literature, we conducted a longitudinal investigation to test the hypothesis that higher baseline CR was associated with a lower risk of developing mobility disability in older adults. Methods Participants were dementia-free older adults who received a brain magnetic resonance imaging and had gait speed assessments during follow-up. Using the residuals approach, CR was derived from the modified-Mini-Mental Status Examination (3MS) total score by removing variance accounted for by measures of structural brain integrity, education and race. Mobility disability was defined using a validated cutoff score in gait speed of 0.8 m/s. Logistic regression models using General Estimating Equations (GEE) were utilized to examine longitudinal associations between baseline CR and the risk of developing of mobility disability across repeated assessments. Results Of the participants (n=237; mean age=82ys; %female=56%) who were free of mobility disability at baseline, 103 developed mobility disability during follow-up (mean=3.1ys). Higher CR at baseline was associated with lower risk of developing incident mobility/disability [odds ratio (OR)=.819, 0.67 to 0.98, p=.038 (unadjusted); OR=.815, 0.67 to 0.99, p=.04 (adjusted for socio-demographic variables and depression); OR=.819, 0.68 to 0.88, p=.035 (adjusted for illness history); OR=.824, 0.68 to 0.99, p=.045 (adjusted for white matter hyperintensities); OR= .795, 0.65 to 0.95, p=.016 (adjusted falls history)]. Conclusion We provided first evidence that higher CR was associated with lower risk of developing mobilitydisability in older adults.

The effect of sex and physical frailty on incident disability after 2 years among community-dwelling older adults: KFACS study

BackgroundThis study investigated the impact of physical frailty on the development of disabilities in mobility, activities of daily living (ADL), and instrumental activities of daily living (IADL) according to sex among community-dwelling Korean older adults.MethodsWe used data of 2,905 older adults aged 70-84 years from the Korean Frailty and Aging Cohort Study (KFACS) at baseline (2016-2017) and Wave 2 (2018-2019). Fried’s physical frailty phenotype was used to identify frailty.ResultsAfter adjustment, frailty showed a higher impact for women than men on developing mobility disability (odds ratio [OR]=14.00, 95% confidence interval [CI]=4.8–40.78 vs. OR=9.89, 95% CI=4.28–22.86) and IADL disability after two years (OR=7.22, 95% CI=2.67–19.56 vs. OR=3.19, 95% CI=1.17–8.70). Pre-frailty led to mobility disability for women and men (OR=2.77, 95% CI=1.93–3.98 vs. OR=2.49, 95% CI=1.66–3.72, respectively), and IADL disability only for women (OR=3.01, 95% CI=1.28–7.09). Among the IADL components, both men and women who were prefrail or frail showed increased disability in ‘using transportation’. Among men, pre-frailty was significantly associated with disability in “going out” and “shopping”. In women, frailty was significantly associated with disability in “doing laundry,” “performing household chores,” “shopping,” and “managing money”.ConclusionsPhysical frailty increased disability over 2 years for women more than men. Physical frailty increased disability in outdoor activity-related IADL components in men and household work-related IADL components in women. This study highlights the need for gender-specific policies and preventative programs for frailty, particularly restorative interventions that focus on women who are physically frail.

How Does Diabetes Accelerate Normal Aging? An Examination of ADL, IADL, and Mobility Disability in Middle-aged and Older Adults With and Without Diabetes

ObjectivesTo build an age norm to quantify and compare the different progression rates of disability in people with and without diabetes. MethodsData were extracted from 5,131 adults aged 50 and older from the Taiwan Longitudinal Study in Aging (TLSA) conducted in 1996. Using multilevel mixed models, the disabilities were measured in 1999, 2003, and 2007. ResultsDiabetes accelerated the occurrence and progression of disabilities during aging. Participants with diabetes developed to mobility, IADL, and ADL at the age of 55, near the age of 60, and near the age of 70, respectively. Diabetes accelerated the onset of disabilities of mobility by 3 years, IADL by 7 years, and ADL by 11 years. In the fully adjusted model, diabetes remains a robust predictor for levels of disability (MobilityβDM = 1.668, p < 0.001, IADLβDM = 1.031, p < 0.001) (IADβDM = 0.690, p < 0.001), and rate of change for developing mobility disability (MobilityβDM*age = 0.088, p < 0.001). ConclusionsThis study showed that diabetes accelerated the occurrence and progression of disabilities starting in middle age. A three to eleven years of acceleration on disability development on mobility, IADL, and ADL was observed.

Incident mobility disability, parkinsonism, and mortality in community-dwelling older adults.

Mobility disability and parkinsonism are associated with decreased survival in older adults. This study examined the transition from no motor impairment to mobility disability and parkinsonism and their associations with death. 867 community-dwelling older adults without mobility disability or parkinsonism at baseline were examined annually. Mobility disability was based on annual measured gait speed. Parkinsonism was based on the annual assessment of 26 items from the motor portion of the Unified Parkinson's Disease Rating Scale. A multistate Cox model simultaneously examined the incidences of mobility disability and parkinsonism and their associations with death. Average age at baseline was 75 years old and 318 (37%) died during 10 years of follow-up. Mobility disability was almost 2-fold more common than parkinsonism. Some participants developed mobility disability alone (42%), or parkinsonism alone (5%), while many developed both (41%). Individuals with mobility disability or parkinsonism alone had an increased risk of death, but their risk was less than the risk in individuals with both impairments. The risk of death did not depend on the order in which impairments occurred. The varied patterns of transitions from no motor impairment to motor impairment highlights the heterogeneity of late-life motor impairment and its contribution to survival. Further studies are needed to elucidate the underlying biology of these different transitions and how they might impact survival.

Plasma proteomic signature of the risk of developing mobility disability: A 9-year follow-up.

IntroductionMobility disability is a powerful indicator of poor health in older adults. The biological and pathophysiological mechanism underlying the development of mobility disability remains unknown. This study conducted a data‐driven discovery phase investigation to identify plasma proteins that predict the incidence of mobility disability in community‐dwelling older adults without mobility disability at baseline.MethodsWe investigated 660 women and men, aged 71.9 ± 6.0 (60–94) years, who participated in the Invecchiare in Chianti, “Aging in the Chianti Area” study and completed the 400‐m walk at fast pace (400‐m walk) at enrollment. Median follow‐up time was 8.57 [interquartile, 3.20–9.08] years. SOMAscan technology was used to measure 1,301 plasma proteins at enrollment. The incident of mobility disability was defined as inability to complete the 400‐m walk. Protein‐specific Cox proportional hazard model was adjusted for sex, age, and other important covariates.ResultsPlasma levels of 75 proteins predicted mobility disability (p < .05). Significant proteins were enriched for the KEGG “PI3K‐Akt signaling,” “phagosomes,” and “cytokine–cytokine receptor interaction” pathways. After multiple comparison adjustment, plasma cathepsin S (CTSS; hazard ratio [HR] 1.33, 95% CI: 1.17, 1.51, q = 0.007), growth/differentiation factor 15 (GDF15; HR: 1.45, 95% CI: 1.23, 1.72, q = 0.007), and thrombospondin‐2 (THBS2; HR: 1.44, 95% CI: 1.22, 1.69, q = 0.007) remained significantly associated with high risk of losing mobility.ConclusionCTSS, GDF15, and THBS2 are novel blood biomarkers associated with new mobility disability in community‐dwelling individuals. Overall, our analysis suggests that cellular senescence and inflammation should be targeted for prevention of mobility disability.

Associations of Usual Pace and Complex Task Gait Speeds With Incident Mobility Disability.

To assess whether gait speed under complex conditions predicts long-term risk for mobility disability as well as or better than usual-pace gait speed. Longitudinal cohort study. Subsample of Health Aging and Body Composition study with follow-up from 2002 to 2003 to 2010 to 2011, including 337 community-dwelling adults (mean age = 78.5 years, 50.7% female, 26.1% black). Associations of gait speed measured under usual-pace, fast-pace, dual-task, and narrow-path conditions with mobility disability, defined by any self-reported difficulty walking ¼ mile assessed annually, were tested by Cox proportional hazard models adjusted for demographic and health characteristics. Models were fitted for each walking condition, and R2 statistics were used to compare predictive value across models. Models were repeated for persistent mobility disability, defined as at least two consecutive years of mobility disability. Mobility disability occurred in 204 (60.5%) participants over the 8-year follow-up. There was a lower hazard of developing mobility disability with faster gait speed under all conditions. Hazard ratios, confidence intervals, and R2 of gait speed predicting mobility disability were similar across all four walking conditions (R2 range = 0.22-0.27), but were strongest for dual-task gait speed (hazard ratio [95% confidence interval], R2 of fully adjusted models = 0.81 [0.75-0.88], 0.27). Results were comparable for persistent mobility disability (R2 range = 0.26-0.28). Slower gait speed under both usual-pace and complex conditions may be a clinical indicator of future risk of mobility disability. These results support the call for increased use of gait speed measures in routine geriatric care. J Am Geriatr Soc 67:2072-2076, 2019.

Incident Mobility Disability, Mild Cognitive Impairment, and Mortality in Community-Dwelling Older Adults

Background/Aims: Mobility disability and mild cognitive impairment (MCI) are common in aging and both are associated with risk of death. This study tested the hypothesis that risk of death differs by the order in which mobility disability and MCI occurred. Methods: One thousand two hundred and sixty-two community-dwelling older adults were unimpaired at baseline and followed annually. Mobility disability was based on measured gait speed, and MCI was based on cognitive performance tests. A multistate Cox model simultaneously examined incidences of mobility disability and MCI to determine whether the order of their occurrence is differentially associated with risk of death. Results: The average age was 75.3 years and 70% were female. While mobility disability occurred more frequently than incident MCI, the subsequent risk of death was higher in participants who developed MCI alone compared to those who developed mobility disability alone (hazard ratio [HR] 1.70, p = 0.018). Of the participants who initially developed mobility disability, about half subsequently developed MCI that doubled their risk of death (HR 2.17, p < 0.001). By contrast, over two-third who developed MCI subsequently developed mobility disability, which did not further increase their risk of death. Conclusion: Mobility disability occurs more frequently in community-dwelling older adults, but MCI is more strongly associated with mortality.

Gender differences in four-year incidence of self-reported and performance-based functional disability: The International Mobility in Aging Study

ObjectivesTo examine differences in incidence of functional disability between older women and men. Methods2002 participants (65–74 years) were recruited in 2012 from Canada, Brazil, Colombia, and Albania, and re-assessed in 2016. Three measures of functional disability were used (1) Difficulty in any of five mobility-related Activities of Daily Living (ADL disability); (2) Self-reported difficulty climbing a flight of stairs or walking 400 m (mobility disability); and (3) Poor physical performance. We estimated the adjusted gender-specific incidence risk ratios (IRR) for each outcome in 2016. ResultsIn 2016, 1506 participants (52% women) were re-examined, 80% of the surviving cohort. Among those not disabled in 2012, seventy-four (12.9%) men developed ADL disability, while 105 (19.2%) developed mobility disability, and 97 (16.1%) developed poor physical performance. For women, numbers were higher 120 (21.4%) developed ADL disability, 117 (26.5%) developed mobility disability, and 140 (23.0%) developed poor physical performance. Compared to men, women had a higher adjusted incidence of self-reported ADL disability (IRR 1.4; 95% CI 1.04–1.88) and mobility disability (IRR 1.4; 95% CI 1.06–1.77), but not of poor physical performance (IRR 1.03; 95% CI 0.88–1.32). ConclusionsAlthough women have a higher self-reported incidence of ADL and mobility disability than men, there was no significant difference in poor physical performance. Reasons for this discrepancy between self-reported and performance-based measures require further investigation. Understanding gender differences in functional disabilities can provide the basis for interventions to prevent mobility loss and minimize any gender gap.

Metabolites Associated With Risk of Developing Mobility Disability in the Health, Aging and Body Composition Study.

Metabolic pathways that give rise to functional decline and mobility disability in older adults are incompletely understood. To identify metabolic perturbations that may affect functional decline, nontargeted metabolomics was used to measure 350 metabolites in baseline plasma from 313 black men in the Health ABC Study (median age 74 years). Usual gait speed was measured over 20 m. Cross-sectional relationships between gait speed and metabolites were explored with partial correlations adjusted for age, study site, and smoking status. Risk of incident mobility disability (two consecutive reports of severe difficulty walking quarter mile or climb 10 stairs) over 13 years of follow-up was explored with Cox regression models among 307 men who were initially free of mobility disability. Significance was determined at p ≤ .01 and q (false discovery rate) ≤ 0.30. Two metabolites were correlated with gait speed: salicylurate (r = -.19) and 2-hydroxyglutarate (r = -.18). Metabolites of amino acids and amino acid degradation (indoxy sulfate; hazard ratio [HR] = 1.48, 95% confidence interval [CI] = 1.09-2.03, symmetric dimethylarginine; HR = 3.58, 95% CI = 1.57-8.15, N-carbamoyl beta-alanine; HR = 1.91, 95% CI = 1.16-3.14, quinolinate; HR = 2.56, 95% CI = 1.65-3.96) and metabolites related to kidney function (aforementioned symmetric dimethylarginine and indoxy sulfate as well as creatinine; HR = 5.91, 95% CI = 2.06-16.9, inositol; HR = 2.70, 95% CI = 1.47-4.97) were among the 23 metabolites associated with incident mobility disability. This study highlights the potential role of amino acid derivatives and products and kidney function early in the development of mobility disability and suggests metabolic profiles could help identify individuals at risk of functional decline.

The Influence of Physical Activity and Sedentary Behavior on Living to Age 85 Years Without Disease and Disability in Older Women.

Whether physical activity (PA) and sedentary behavior influence the odds of women living to age 85 years without chronic disease or disability is not well described. Participants of the Women's Health Initiative (n = 49,612) were categorized based on health status by age 85 years: (i) lived without developing major chronic disease or mobility disability ("healthy"); (ii) lived and developed mobility disability with or without disease; (iii) lived and developed major chronic disease, but not mobility disability; and (iv) died before their 85th birth year. Multinomial logistic regression models that adjusted for covariates such as age, race/ethnicity, and body size estimated associations of self-reported PA and sitting time on developing major disease or mobility disability or dying before age 85 relative to being healthy. Mean ± SD baseline age was 70.2 ± 3.6 years. Distributions were: 22% healthy, 23% had mobility disability, 26% had major disease, and 29% died. Relative to those with high total PA, the adjusted odds ratios (OR) (confidence intervals [CI]) for mobility disability was 1.6 (1.4-1.7), 1.2 (1.1-1.3), and 1.1 (1.0-1.2) for women with no, low, and moderate total PA, respectively (p-trend < .001). The corresponding covariate-adjusted OR (CI) for mortality was 1.7 (1.5-1.8), 1.2 (1.1-1.3), and 1.0 (1.0-1.1) (p-trend < .001). Total PA was not associated with developing chronic disease before age 85 years. Sitting ≥10 relative to <5 hours per day increased the odds of mobility disability (1.1, CI: 1.0-1.3) and mortality (1.2, CI: 1.0-1.3) prior to age 85 years (p < .001). Increasing PA to recommended levels and reducing sitting time are modifiable behaviors that may improve healthy aging in older women.

Calf circumference predicts mobility disability: A secondary analysis of the Mexican health and ageing study

IntroductionCalf circumference is a surrogate measurement of muscle mass. However, there is scarce evidence on its validity in predicting adverse outcomes such as mobility disability. The aim of this report is to determine if calf circumference could predict incident mobility disability in Mexican 60-year or older adults. MethodsThis is a secondary analysis of the Mexican Health and Aging Study and in particular of its two first waves. Sixty-year or older adults without mobility disability in the first assessment were included and followed-up for two years. Calf circumference quartile groups were compared to test the difference of incident mobility disability. Logistic regression models were fitted to test the independent association when including confounding variables. ResultsA total of 745 older adults were assessed, from which 24.4% of the older adults developed mobility disability at follow-up. A calf circumference>38cm was associated with a higher risk of developing mobility disability, even after adjustment in the multivariate model, with an odds ratio 0.55 (95% confidence interval 0.31–0.99, P=0.049). ConclusionsHigh calf circumference in Mexican older adults is independently associated with incident mobility disability. This could reflect the impact of adverse health conditions such as obesity (with high fat tissue) or edema. Further research should aim at testing these results in different populations.

Sensory and Motor Peripheral Nerve Function and Incident Mobility Disability

To assess the relationship between sensorimotor nerve function and incident mobility disability over 10 years. Prospective cohort study with longitudinal analysis. Two U.S. clinical sites. Population-based sample of community-dwelling older adults with no mobility disability at 2000/01 examination (N = 2,148 [Corrected]; mean age ± SD 76.5 ± 2.9, body mass index 27.1 ± 4.6; 50.2% female, 36.6% black, 10.7% with diabetes mellitus). Motor nerve conduction amplitude (poor <1 mV) and velocity (poor <40 m/s) were measured on the deep peroneal nerve. Sensory nerve function was measured using 10- and 1.4-g monofilaments and vibration detection threshold at the toe. Lower extremity symptoms included numbness or tingling and aching or burning pain. Incident mobility disability assessed semiannually over 8.5 years (interquartile range 4.5-9.6 years) was defined as two consecutive self-reports of a lot of difficulty or inability to walk one-quarter of a mile or climb 10 steps. Nerve impairments were detected in 55% of participants, and 30% developed mobility disability. Worse motor amplitude (HR = 1.29 per SD, 95% CI = 1.16-1.44), vibration detection threshold (HR = 1.13 per SD, 95% CI = 1.04-1.23), symptoms (HR = 1.65, 95% CI = 1.26-2.17), two motor impairments (HR = 2.10, 95% CI = 1.43-3.09), two sensory impairments (HR = 1.91, 95% CI = 1.37-2.68), and three or more nerve impairments (HR = 2.33, 95% CI = 1.54-3.53) predicted incident mobility disability after adjustment. Quadriceps strength mediated relationships between certain nerve impairments and mobility disability, although most remained significant. Poor sensorimotor nerve function independently predicted mobility disability. Future work should investigate modifiable risk factors and interventions such as strength training for preventing disability and improving function in older adults with poor nerve function.

Weight change, body composition, and risk of mobility disability and mortality in older adults: a population-based cohort study.

To examine associations between weight change, body composition, risk of mobility disability, and mortality in older adults. Prospective, longitudinal, population-based cohort. The Health, Aging, and Body Composition Study. Women (n=1,044) and men (n=931) aged 70 to 79. Weight and lean and fat mass from dual-energy X-ray absorptiometry measured annually over 5years. Weight was defined as stable (n=664, reference), loss (n=662), gain (n=321), or cycling (gain and loss, n=328) using change of 5% from year to year or from Year 1 to 6. Mobility disability (two consecutive reports of difficulty walking one-quarter mile or climbing 10 steps) and mortality were determined for 8years after the weight change period. Associations were analyzed using Cox proportional hazards regression adjusted for covariates. During follow-up, 313 women and 375 men developed mobility disability, and 322 women and 378 men died. There was no risk of mobility disability or mortality with weight gain. Weight loss (hazard ratio (HR)=1.88, 95% confidence interval (CI)=1.40-2.53) and weight cycling (HR=1.59, 95% CI=1.11-2.29) were associated with mobility disability in women, and weight loss was associated with mobility disability in men (HR=1.30, 95% CI=1.01-1.69). Weight loss and weight cycling were associated with mortality risk in women (weight loss: HR=1.47, 95% CI=1.07-2.01; weight cycling: HR=1.62, 95% CI=1.15-2.30) and in men (weight loss: HR=1.41, 95% CI=1.09-1.83; weight cycling: HR=1.50, 95% CI=1.08-2.08). Adjustment for lean and fat mass and change in lean and fat mass from Year 1 to 6 attenuated the relationships between weight loss and mobility disability in men and between weight loss and mortality in men and women. Weight cycling and weight loss predict impending mobility disability and mortality in old age, underscoring the prognostic importance of weight history.

Obesity and Late-Age Survival Without Major Disease or Disability in Older Women

The effect of obesity on late-age survival in women without disease or disability is unknown. To investigate whether higher baseline body mass index and waist circumference affect women's survival to 85 years of age without major chronic disease (coronary disease, stroke, cancer, diabetes mellitus, or hip fracture) and mobility disability. Examination of 36,611 women from the Women's Health Initiative observational study and clinical trial programs who could have reached 85 years or older if they survived to the last outcomes evaluation on September 17, 2012. Recruitment was from 40 US clinical centers from October 1993 through December 1998. Multinomial logistic regression models were used to estimate odds ratios and 95% CIs for the association of baseline body mass index and waist circumference with the outcomes, adjusting for demographic, behavioral, and health characteristics. Mutually exclusive classifications: (1) survived without major chronic disease and without mobility disability (healthy); (2) survived with 1 or more major chronic disease at baseline but without new disease or disability (prevalent diseased); (3) survived and developed 1 or more major chronic disease but not disability during study follow-up (incident diseased); (4) survived and developed mobility disability with or without disease (disabled); and (5) did not survive (died). Mean (SD) baseline age was 72.4 (3.0) years (range, 66-81 years). The distribution of women classified as healthy, prevalent diseased, incident diseased, disabled, and died was 19.0%, 14.7%, 23.2%, 18.3%, and 24.8%, respectively. Compared with healthy-weight women, underweight and obese women were more likely to die before 85 years of age. Overweight and obese women had higher risks of incident disease and mobility disability. Disability risks were striking. Relative to healthy-weight women, adjusted odds ratios (95% CIs) of mobility disability were 1.6 (1.5-1.8) for overweight women and 3.2 (2.9-3.6), 6.6 (5.4-8.1), and 6.7 (4.8-9.2) for class I, II, and III obesity, respectively. Waist circumference greater than 88 cm was also associated with higher risk of earlier death, incident disease, and mobility disability. Overall and abdominal obesity were important and potentially modifiable factors associated with dying or developing mobility disability and major chronic disease before 85 years of age in older women.

Chronic Kidney Disease Defined by Cystatin C Predicts Mobility Disability and Changes in Gait Speed: The Framingham Offspring Study

As creatinine-based estimates of renal function are inaccurate in older adults, an alternative is an estimated glomerular filtration rate (eGFR(cys)) based on cystatin C. We examined the prospective association between chronic kidney disease (CKD(cys)) as determined by eGFR(cys) with the primary outcome of incident mobility disability and the secondary outcome of change in gait speed. Framingham Offspring Study participants older than 60 years and free of mobility disability at baseline (1998-2001) were eligible. Baseline CKD(cys) was defined as eGFR(cys) less than 60 mL/min/1.73 m(2). At follow-up (2005-2008), the outcomes of mobility disability, defined as self-reported inability to walk 1/2 mile and/or climb a flight of stairs, and gait speed were measured. Logistic and linear regression models were adjusted for age, sex, body mass index, smoking, diabetes, C reactive protein, and physical activity. Of 1,226 participants, 230 (19%) had CKD(cys) at baseline. After a mean follow-up of 6.6 years, 185 (15%) developed mobility disability. Of those with CKD(cys), 60 (26%) developed mobility disability. Those with CKD(cys) had greater odds of mobility disability in the age- and sex-adjusted (odds ratio [OR] 1.91, 95% CI 1.32, 2.75) and fully adjusted (OR 1.55, 95% CI 1.05, 2.31) models compared with those without CKD(cys). In fully adjusted models, participants with CKD(cys) had greater gait speed declines than those without CKD(cys) (β = 0.07 [SE 0.02], p = .0022). CKD(cys) was associated with higher odds of incident mobility disability and greater decline in gait speed, highlighting the loss of physical independence in elders with CKD.

Relation of Late-Life Social Activity With Incident Disability Among Community-Dwelling Older Adults

We tested the hypothesis that a higher level of social activity was associated with decreased risk of incident disability in older adults. Data came from older adults in the Rush Memory and Aging Project, an ongoing longitudinal cohort study of aging. Analyses were restricted to persons without clinical dementia and reporting no need for help performing any task in the particular functional domain assessed. Participants were followed for an average of 5.1 years (SD = 2.5). Social activity, based on 6 items (visiting friends or relatives; going to restaurants, sporting events, or playing games; group meetings; church/religious services; day or overnight trips; unpaid community/volunteer work), was assessed at baseline. Disability in basic activities of daily living, mobility disability, and instrumental activities of daily living was assessed annually. Proportional hazard models adjusted for age, sex, and education were used to examine the association between social activity and incident disability. Fully adjusted models included terms for depression, vascular diseases and risk factors, body mass index, social networks, and self-reported physical activity. In fully adjusted models, among 954 persons without baseline disability, the risk of developing disability in activities of daily living decreased by 43% (hazard ratio = 0.57, 95% confidence interval = 0.46, 0.71) for each additional unit of social activity. Social activity was also associated with decreased risk of developing mobility disability (hazard ratio = 0.69, 95% confidence interval = 0.54, 0.88) and disability in instrumental activities of daily living (hazard ratio = 0.71, 95% confidence interval = 0.55, 0.93). Social activity is associated with a decreased risk of incident disability in activities of daily living, mobility, and instrumental activities of daily living, among community-dwelling older adults.

The effect of obesity combined with low muscle strength on decline in mobility in older persons: results from the InCHIANTI Study

Both obesity and muscle impairment are increasingly prevalent among older persons and negatively affect health and physical functioning. However, the combined effect of coexisting obesity and muscle impairment on physical function decline has been little studied. We examined whether obese persons with low muscle strength experience significantly greater declines in walking speed and mobility than persons with only obesity or low muscle strength. Community-dwelling adults aged > or = 65 years (n = 930) living in the Chianti geographic area (Tuscany, Italy) were followed for 6 years in the population-based InCHIANTI study. On the basis of baseline measurements (1998-2000), obesity was defined as body mass index (BMI) > or = 30 kg/m(2) and low muscle strength as lowest sex-specific tertile of knee extensor strength. Walking speed and self-reported mobility disability (ability to walk 400 m or climb one flight of stairs) were assessed at baseline and at 3- and 6-year follow-up. At baseline, obese persons with low muscle strength had significantly lower walking speed compared with all other groups (P < or = 0.05). In longitudinal analyses, obese participants with low muscle strength had steeper decline in walking speed and high risk of developing new mobility disability over the 6-year follow-up compared with those without obesity or low muscle strength. After the age of 80, the differences between groups were substantially attenuated. The differences seen in walking speed across combination of low muscle strength and obesity groups were partly explained by 6-year changes in muscle strength, BMI and waist circumference. Obesity combined with low muscle strength increases the risk of decline in walking speed and developing mobility disability, especially among persons < 80 years old.

The effects of social networks on disability in older Australians.

To investigate the effects of total social networks and specific social networks with children, relatives, friends, and confidants on disability in mobility and Nagi functional tasks. Six waves of data from the Australian Longitudinal Study of Ageing were used. Data came from 1,477 participants aged 70 years or older. The effects of total social networks and those with children, relatives, friends, and confidants on transitions in disability status were analyzed using binary and multinomial logistic regression. After controlling for a range of health, environmental, and personal factors, social networks with relatives were protective against developing mobility disability (OR = 0.89; 95% CI = 0.79 to 1.00) and Nagi disability (OR = 0.85; 95% CI = 0.74 to 0.96). Other social subnetworks did not have a consistent effect on the development of disability. The effects of social relationships extend beyond disability in activities of daily living. Networks with relatives protect against disability in mobility and Nagi tasks.