Person-Specific Contributions of Brain Pathologies to Progressive Parkinsonism in Older Adults

Update: Descriptive epidemiology of Parkinson disease

We review the descriptive epidemiology of Parkinson disease (PD). PD is a prevalent neurologic disorder in high Socio-Demographic Index (SDI) nations with rising prevalence in low and middle SDI nations. PD became a prevalent disorder in high SDI nations during the 20th century. Population growth, population aging, and increased disease duration are major drivers of rising PD prevalence. Exposure to industrial toxicants may also be a contributor to rising PD prevalence. PD is an age-related disorder with incidence likely peaking in the 8th decade of life and prevalence in the 9th decade of life. PD is notable for significant sex difference in PD risk with greater risk in men. There may be ancestral differences in PD prevalence and risk. PD is associated with moderately increased mortality though this may be underestimated. Despite significant research, there is considerable uncertainty about basic features of PD epidemiology.

Relation of Motor Impairments to Neuropathologic Changes of Limbic-Predominant Age-Related TDP-43 Encephalopathy in Older Adults

BACKGROUND AND OBJECTIVES

Limbic-predominant age-related transactive response DNA-binding protein 43 (TDP-43) encephalopathy neuropathologic change (LATE-NC) is common and is a major contributor to cognitive decline and Alzheimer dementia in older adults. The objective of the current study was to examine whether LATE-NC was also associated with declining motor function in older adults.

METHODS

Participants were from 2 longitudinal clinical pathologic studies of aging who did not have dementia at the time of enrollment. Postmortem pathologic examination included immunohistochemical staining for TDP-43 in 8 brain regions, which was summarized as a dichotomous variable indicating advanced LATE-NC stages at which TDP-43 pathology had accumulated in the hippocampus, entorhinal, or neocortical regions. Annual motor testing included maximal inspiratory and expiratory pressures (summarized as respiratory muscle strength), grip and pinch strength (summarized as hand strength), finger tapping speed and the Purdue Pegboard Test (summarized as hand dexterity), and walking 8 feet and turning 360° (summarized as gait function). The severity of parkinsonism was also assessed and summarized as a global parkinsonism score. Global cognition was a summary of standardized scores of 19 neuropsychological tests. We used linear mixed-effect models to examine the associations of LATE-NC with longitudinal changes of motor decline and used multivariate random coefficient models to simultaneously examine the associations of LATE-NC with cognitive and motor decline.

RESULTS

Among 1,483 participants (mean age at death 90.1 [SD = 6.4] years, 70% women, mean follow-up 7.4 [SD = 3.8] years), LATE-NC was present in 34.0% (n = 504). In separate linear mixed-effect models controlling for demographics and other brain pathologies, LATE-NC was associated with faster decline in respiratory muscle strength (estimate = -0.857, SE = 0.322, p = 0.008) and hand strength (estimate = -0.005, SE = 0.002, p = 0.005) but was not related to hand dexterity, gait function, or parkinsonism. In multivariate random coefficient models including respiratory muscle strength, hand strength, and global cognition as the outcomes, LATE-NC remained associated with a faster respiratory muscle strength decline rate (estimate = -0.021, SE = 0.009, p = 0.023), but the association with hand strength was no longer significant (estimate = -0.002, SE = 0.003, p = 0.390).

DISCUSSION

Motor impairment, specifically respiratory muscle weakness, may be an unrecognized comorbidity of LATE-NC that highlights the potential association of TDP-43 proteinopathy with noncognitive phenotypes in aging adults.

Correlated decline of cognitive and motor phenotypes and ADRD pathologies in old age

INTRODUCTION

Examining motor and cognitive decline in separate models may underestimate their associations.

METHODS

In a single trivariate model, we examined the levels and rates of decline of three phenotypes, sensor-derived total daily physical activity, motor abilities, and cognition in 1007 older adults during 6 years of follow-up. In 477 decedents, we repeated the model adding fixed terms for indices of nine brain pathologies.

RESULTS

Simultaneous rates of decline of all three phenotypes showed the strongest correlations with shared variance of up to 50%. Brain pathologies explained about 3% of the variance of declining daily physical activity, 9% of declining motor abilities, and 42% of cognitive decline.

DISCUSSION

The rates of declining cognitive and motor phenotypes are strongly correlated and measures of brain pathologies account for only a small minority of their decline. Further work is needed to elucidate the biology underlying correlated cognitive and motor decline in aging adults.

Correlates of Person-Specific Rates of Change in Sensor-Derived Physical Activity Metrics of Daily Living in the Rush Memory and Aging Project

This study characterized person-specific rates of change of total daily physical activity (TDPA) and identified correlates of this change. TDPA metrics were extracted from multiday wrist-sensor recordings from 1083 older adults (average age 81 years; 76% female). Thirty-two covariates were collected at baseline. A series of linear mixed-effect models were used to identify covariates independently associated with the level and annual rate of change of TDPA. Though, person-specific rates of change varied during a mean follow-up of 5 years, 1079 of 1083 showed declining TDPA. The average decline was 16%/year, with a 4% increased rate of decline for every 10 years of age older at baseline. Following variable selection using multivariate modeling with forward and then backward elimination, age, sex, education, and 3 of 27 non-demographic covariates including motor abilities, a fractal metric, and IADL disability remained significantly associated with declining TDPA accounting for 21% of its variance (9% non-demographic and 12% demographics covariates). These results show that declining TDPA occurs in many very old adults. Few covariates remained correlated with this decline and the majority of its variance remained unexplained. Further work is needed to elucidate the biology underlying TDPA and to identify other factors that account for its decline.

Neurodegenerative and Cerebrovascular Brain Pathologies Are Differentially Associated With Declining Grip Strength and Gait In Older Adults

BACKGROUND

Understanding the pathological bases underlying the heterogeneity of motor decline in old age may lead to targeted treatments. We examined whether different brain pathologies are related to declining grip strength and gait function.

METHODS

We examined postmortem brains of older adults who underwent annual motor testing. Postmortem exam measured 6 neurodegenerative and 5 cerebrovascular disease (CVD) pathologies. Grip strength was measured twice bilaterally using a hand-held dynamometer, and gait function was a composite measure based on time and steps taken to walk 8 ft and perform a 360° turn twice.

RESULTS

In separate linear mixed-effects models including all autopsied adults (N = 1 217), neurodegenerative pathologies including tau tangles, TDP-43, and nigral neuronal loss were associated with declining grip strength, but not CVD pathologies. In contrast, although both CVD and neurodegenerative pathologies were associated with declining gait function, CVD pathologies accounted for 75% of the variance of declining rate of gait function explained by brain pathologies and neurodegenerative pathologies accounted for 25%. These findings were unchanged in adults (n = 970) without a history of stroke. Restricting analyses to only adults without dementia (n = 661), CVD pathologies continued to account for the majority of the variance of declining gait. However, we failed to detect in this subgroup the variance of declining grip strength explained by neurodegenerative or CVD pathologies.

CONCLUSION

Different pathologies accumulating in aging brains may contribute to the phenotypic heterogeneity of motor decline. Larger studies are needed in older adults without dementia to assess differences in the motor consequences of varied brain pathologies.

Proteome-Wide Discovery of Cortical Proteins That May Provide Motor Resilience to Offset the Negative Effects of Pathologies in Older Adults

BACKGROUND

Motor resilience proteins have not been identified. This proteome-wide discovery study sought to identify proteins that may provide motor resilience.

METHODS

We studied the brains of older decedents with annual motor testing, postmortem brain pathologies, and proteome-wide data. Parkinsonism was assessed using 26 items of a modified United Parkinson Disease Rating Scale. We used linear mixed-effect models to isolate motor resilience, defined as the person-specific estimate of progressive parkinsonism after controlling for age, sex, and 10 brain pathologies. A total of 8 356 high-abundance proteins were quantified from dorsal lateral prefrontal cortex using tandem mass tag and liquid chromatography-mass spectrometry.

RESULTS

There were 391 older adults (70% female), mean age 80 years at baseline and 89 years at death. Five proteins were associated with motor resilience: A higher level of AP1B1 (Estimate -0.504, SE 0.121, p = 3.12 × 10-5) and GNG3 (Estimate -0.276, SE 0.068, p = 4.82 × 10-5) was associated with slower progressive parkinsonism. By contrast, a higher level of TTC38 (Estimate 0.140, SE 0.029, p = 1.87 × 10-6), CARKD (Estimate 0.413, SE 0.100, p = 3.50 × 10-5), and ABHD14B (Estimate 0.175, SE 0.044, p = 6.48 × 10-5) was associated with faster progressive parkinsonism. Together, these 5 proteins accounted for almost 25% of the variance of progressive parkinsonism above the 17% accounted for by 10 indices of brain pathologies.

DISCUSSION

Cortical proteins may provide more or less motor resilience in older adults. These proteins are high-value therapeutic targets for drug discovery that may lead to interventions that maintain motor function despite the accumulation of as yet untreatable brain pathologies.

Mixed pathology as a rule, not exception: Time to reconsider disease nosology

Parkinson's disease is a progressive neurodegenerative disorder that is associated with motor and nonmotor symptoms. Accumulation of misfolded α-synuclein is considered a key pathological feature during disease initiation and progression. While clearly deemed a synucleinopathy, the development of amyloid-β plaques, tau-containing neurofibrillary tangles, and even TDP-43 protein inclusions occur within the nigrostriatal system and in other brain regions. In addition, inflammatory responses, manifested by glial reactivity, T-cell infiltration, and increased expression of inflammatory cytokines, plus other toxic mediators derived from activated glial cells, are currently recognized as prominent drivers of Parkinson's disease pathology. However, copathologies have increasingly been recognized as the rule (>90%) and not the exception, with Parkinson's disease cases on average exhibiting three different copathologies. While microinfarcts, atherosclerosis, arteriolosclerosis, and cerebral amyloid angiopathy may have an impact on disease progression, α-synuclein, amyloid-β, and TDP-43 pathology do not seem to contribute to progression.

Role of endocrine PACAP in age-related diseases

Pituitary adenylate cyclase activating polypeptide (PACAP) is a conserved neuropeptide, which confers diverse anti-aging endocrine and paracrine/autocrine effects, including anti-apoptotic, anti-inflammatory and antioxidant action. The results of the in vivo and in vitro experiments show that increasing emphasis is being placed on the diagnostic/prognostic biomarker potential of this neuropeptide in a wide array of age-related diseases. After the initial findings regarding the presence and alteration of PACAP in different body fluids in physiological processes, an increasing number of studies have focused on the changes of its levels in various pathological conditions associated with advanced aging. Until 2016 - when the results of previous human studies were reviewed - a vast majority of the studies had dealt with age-related neurological diseases, like cerebrovascular and neurodegenerative diseases, multiple sclerosis, as well as some other common diseases in elderly such as migraine, traumatic brain injury and post-traumatic stress disorder, chronic hepatitis and nephrotic syndrome. The aim of this review is to summarize the old and the new results and highlight those 'classical' and emerging clinical fields in which PACAP may become subject to further investigation as a diagnostic and/or prognostic biomarker in age-related diseases.

Mixed Neuropathologies, Neural Motor Resilience and Target Discovery for Therapies of Late-Life Motor Impairment

By age 85, most adults manifest some degree of motor impairment. However, in most individuals a specific etiology for motor decline and treatment to modify its inexorable progression cannot be identified. Recent clinical-pathologic studies provide evidence that mixed-brain pathologies are commonly associated with late-life motor impairment. Yet, while nearly all older adults show some degree of accumulation of Alzheimer's disease and related dementias (ADRD) pathologies, the extent to which these pathologies contribute to motor decline varies widely from person to person. Slower or faster than expected motor decline in the presence of brain injury and/or pathology has been conceptualized as more or less "resilience" relative to the average person This suggests that other factors, such as lifestyles or other neurobiologic indices may offset or exacerbate the negative effects of pathologies via other molecular pathways. The mechanisms underlying neural motor resilience are just beginning to be illuminated. Unlike its cousin, cognitive resilience which is restricted to neural mechanisms above the neck, the motor system extends the total length of the CNS and beyond the CNS to reach muscle and musculoskeletal structures, all of which are crucial for motor function. Building on prior work, we propose that by isolating motor decline unrelated to neuropathologies and degeneration, investigators can identify genes and proteins that may provide neural motor resilience. Elucidating these molecular mechanisms will advance our understanding of the heterogeneity of late-life motor impairment. This approach will also provide high value therapeutic targets for drug discovery of therapies that may offset the negative motor consequences of CNS pathologies that are currently untreatable.

Association of Statins With Cerebral Atherosclerosis and Incident Parkinsonism in Older Adults

BACKGROUND

The burden of cerebrovascular disease pathologies is associated with progressive parkinsonism in older adults. We tested the hypothesis that older adults using statins have a lower risk of developing parkinsonism.

METHODS

We studied older adults with annual clinical testing of four parkinsonian signs and assessment of statin use based on inspection of all medications. Parkinsonism was present if there was clinical evidence of 2 or more parkinsonian signs. Postmortem brain exam collected indices of pathologies including atherosclerosis of the large vessels of the Circle of Willis. We examined if baseline statin use was related to incident parkinsonism. Then in decedents, we examined whether statin use prior to death was related to pathologies and whether pathologies linked the association of statin use with parkinsonism.

RESULTS

Mean age of the participants (n=2841) at study baseline was 76.3 (SD=7.4) years, and 75% were women. During an average follow-up of 6 years (mean=5.6, SD=4.9), 50% (n=1432) of participants developed parkinsonism. Statin use at baseline (n=936) was associated with a lower risk of parkinsonism (HR=0.84, 95%CI: 0.74-0.96, p=0.008) controlling for demographics, vascular risk factors and diseases. Among the decedents [n=1044, age at death (mean=89.2, SD=6.7)], statin-use prior to death was associated with a lower odds of atherosclerosis (OR=0.63, 95%CI: 0.50-0.79, p<0.001). In a mediation analysis, both a direct (OR=0.73, 95%CI: 0.54-0.93, p=0.008) and an indirect (OR=0.92, 95%CI: 0.88-0.97, p=0.002) pathway via less severe atherosclerosis linked statins to parkinsonism indicating that atherosclerosis mediated 17% of the association between statins and parkinsonism.

CONCLUSION

Adults using statins have a lower risk of parkinsonism that may be partially mediated by a lower odds of brain atherosclerosis. These findings highlight the role of cerebrovascular pathologies in late-life parkinsonism and suggest a potential role for statins in decreasing its magnitude.

Neuropathological substrates of cognition in Parkinson's disease

Autopsy validation is still required for a definitive diagnosis of Parkinson's disease (Postuma et al., 2015), where the presence of Lewy bodies and Lewy neurites, composed primarily of alpha-synuclein, are observed in stereotyped patterns throughout regions of the brainstem, limbic, and neocortical regions of the brain (Braak et al., 2003). In spite of these relatively reliable observed patterns of alpha-synuclein pathology, there is a large degree of heterogeneity in the timing and features of neuropsychiatric and cognitive dysfunction in Parkinson's disease (Fereshtehnejad et al., 2015; Selikhova et al., 2009; Williams-Gray et al., 2013). Detailed studies of their neuropathological substrates of cognitive dysfunction and their associations with a variety of in vivo biomarkers have begun to disentangle this complex relationship, but ongoing multicentered, longitudinal studies of well-characterized and autopsy validated cases are still required.

Association of White Matter Hyperintensities With Pathology and Progression of Parkinsonism in Aging

Importance

Progressive parkinsonism is common in older adults without a diagnosis of Parkinson disease and is associated with adverse health outcomes, but its pathologic basis is controversial.

Objective

To examine if the burden of cerebral white matter hyperintensity (WMH), a common manifestation of cerebrovascular disease pathologies, is associated with the rate of progressive parkinsonism.

Design, Setting, and Participants

This community-based cohort study included participants recruited in 3 ongoing cohorts that began enrollment in 1994, 1997, and 2004. Prior to death, participants were observed for a mean of 7.5 years, with annual clinical assessments. From 4427 participants enrolled in the 3 cohorts, 2134 died. Postmortem autopsy was performed in 1725 decedents, and 598 also had ex vivo brain magnetic resonance imaging. Participants were excluded if they were missing any of the 9 postmortem pathology indices (n = 22) or repeated parkinsonism assessment (n = 41) or had received a clinical diagnosis of Parkinson disease at any point before or during the study (n = 19). Data were analyzed from April 2020 to August 2021.

Exposures

WMH burden was assessed using a modified Fazekas rating scale.

Main Outcomes and Measures

Parkinsonism was assessed annually using 26 items of a modified motor portion of the Unified Parkinson's Disease Rating Scale. A summary score was developed from the item scores, with higher scores indicating more severe parkinsonism.

Results

Of 516 included decedents, 364 (70.5%) were female, and the mean (SD) age at death was 90.2 (6.4) years. Higher WMH was associated with faster progressive parkinsonism (estimate, 0.024; SE, 0.008; P = .002). The attenuation of this association was greater when controlling for indices of cerebrovascular disease pathologies than when controlling for neurodegenerative pathologies (cerebrovascular disease: estimate, 0.019; SE, 0.008; P = .02; neurodegenerative: estimate, 0.022; SE, 0.008; P = .003), but both remained significant.

Conclusions and Relevance

In this cohort study, higher levels of both WMH and indices of cerebrovascular disease pathologies in aging brains were associated with more rapid progressive parkinsonism. Further studies are needed to determine if in vivo brain imaging of older adults for evidence of WMH and aggressive medical treatment of vascular risk factors and diseases can reduce the occurrence or severity of late-life parkinsonism.

Association of Lewy Bodies With Age-Related Clinical Characteristics in Black and White Decedents

OBJECTIVE

The associations of Lewy bodies (LBs) with olfactory dysfunction, parkinsonism, and higher odds of dementia were assessed in Black and White community-dwelling elders and racial differences in these associations were tested.

METHODS

Black decedents (n = 81) were matched 2-to-1 by age, sex, years of education, and follow-up time in the study with White decedents (n = 154) from 4 longitudinal studies of dementia and aging. Participants underwent uniform clinical examination and cognitive, motor, and olfactory testing. LBs were detected in 7 brain regions by α-synuclein immunohistochemistry and racial differences in their association with olfaction, parkinsonism, and odds of dementia were determined using regression analyses.

RESULTS

The mean scores of the odor test, global parkinsonism signs, and global cognition were lower in Black than White decedents; the frequency of dementia was similar in both groups. The frequency of LBs was similar in Black and White decedents (∼25%), as was the frequency of LBs in individual brain regions, while the mean LB counts/mm2 were similar in all regions except the cingulate cortex, which showed higher mean LB counts in Black decedents. In regression analyses, LBs were associated with impaired olfaction (-2.23, 95% confidence interval [CI] -3.45 to -1.01) and higher odds of dementia (odds ratio 3.0, 95% CI 1.10-8.17) in both racial groups; an association with parkinsonism was stronger in Black than White decedents.

CONCLUSIONS

The frequency, distribution, and clinical manifestations of LBs are similar in Black and White elders.

Frequency of Parkinsonism and Parkinson Disease in African Americans in the Chicago Community

BACKGROUND

There is paucity of data about African American (AA) patients with Parkinson's disease (PD) and parkinsonism which may precede PD in older adults. Prior studies suggest that there are lower rates of PD in the AA population, with more cognitive impairment in AA with PD. This study aimed to investigate differences in PD, parkinsonism, and cognition between White and AA populations in 3 longitudinal epidemiologic cohort studies of aging.

METHODS

This study examined parkinsonism, PD frequency, and cognition of community-dwelling older individuals in 3 longitudinal epidemiologic cohort studies. Parkinsonism was based on an exam utilizing the modified Unified Parkinson's Disease Rating Scale performed by a nurse. PD was based on self-report, medications used for treatment of PD, and examination findings. Cognition was assessed using 19 performance-based tests that assess 5 cognitive domains.

RESULTS

AA participants were less likely to have parkinsonism compared to Whites, even with age and gender differences. Frequency of PD was not significant between groups. AA were more likely to have lower cognitive scores as compared to Whites. AA were less likely to have parkinsonism even with controlling for cognitive differences between groups.

CONCLUSIONS

Parkinsonian signs are present among AA in the community at lower rates than in White individuals. Cognitive profiles of AA and Whites with parkinsonism may be different, suggesting differing contributions of pathology to cognitive decline and parkinsonism between groups. Additional research is needed to understand the progression of parkinsonism to PD, as well as to understanding the cognitive differences in AA with parkinsonism.

Association of Hemoglobin A1C With TDP-43 Pathology in Community-Based Elders

OBJECTIVE

To test the hypothesis that an inverse association exists between diabetes mellitus (DM) and hemoglobin A1C (A1C) with transactive response DNA binding protein 43 (TDP-43) levels in older adults.

METHODS

We leveraged antemortem and postmortem data of decedents from 3 community-based clinical-pathologic studies. DM status, A1C levels, and medications for DM were documented annually. TDP-43 cytoplasmic inclusions, evaluated in 6 brain regions using immunohistochemistry, were used to obtain a semiquantitative TDP-43 score (0-5) in each region, and scores were averaged across regions to obtain a TDP-43 severity score. We used linear regressions to test the association of DM and A1C with the TDP-43 severity score.

RESULTS

On average, participants (n = 817) were 90 years old at the time of death, three-fourths were women, and one-fourth had DM. The mean A1C was 6.0% (SD 0.6). TDP-43 was observed in 54% of participants, and the mean TDP-43 score was 0.7 (range 0-4.5). A higher level of A1C was associated with a lower TDP-43 score (estimate -0.156, SE 0.060, p = 0.009), while DM had a borderline inverse association with the TDP-43 score (estimate -0.163, SE 0.087, p = 0.060). The association of higher levels of A1C with lower TDP-43 scores persisted after further adjustment by APOE ε4, vascular risk factors, stroke, and hypoglycemic medications. Exclusion of the oldest old participants did not change the results.

CONCLUSION

Overall, the results suggest that a high level of A1C is associated with less TDP-43 proteinopathy in older persons while the relationship of DM with TDP-43 needs further study.

Cortical proteins may provide motor resilience in older adults

Motor resilience proteins may be a high value therapeutic target that offset the negative effects of pathologies on motor function. This study sought to identify cortical proteins associated with motor decline unexplained by brain pathologies that provide motor resilience. We studied 1226 older decedents with annual motor testing, postmortem brain pathologies and quantified 226 proteotypic peptides in prefrontal cortex. Twenty peptides remained associated with motor decline in models controlling for ten brain pathologies (FDR < 0.05). Higher levels of nine peptides and lower levels of eleven peptides were related to slower decline. A higher motor resilience protein score based on averaging the levels of all 20 peptides was related to slower motor decline, less severe parkinsonism and lower odds of mobility disability before death. Cortical proteins may provide motor resilience. Targeting these proteins in further drug discovery may yield novel interventions to maintain motor function in old age.

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

Background

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.

Methods

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.

Results

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.

Conclusion

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.

Motor function is the primary driver of the associations of sarcopenia and physical frailty with adverse health outcomes in community-dwelling older adults

Background

This study tested the hypothesis that sarcopenia and its constituent components, reduced lean muscle mass and impaired motor function, are associated with reduced survival and increased risk of incident disabilities.

Methods

1466 community-dwelling older adults underwent assessment of muscle mass with bioelectrical impedance analysis (BIA), grip strength, gait speed and other components of physical frailty and annual self-report assessments of disability. We used Cox proportional hazards models that controlled for age, sex, race, education and height to examine the associations of a continuous sarcopenia metric with the hazard of death and incident disabilities.

Results

Mean baseline age was about 80 years old and follow-up was 5.5 years. In a proportional hazards model controlling for age, sex, race, education and baseline sarcopenia, each 1-SD higher score on a continuous sarcopenia scale was associated with lower hazards of death (HR 0.70, 95%CI [0.62, 0.78]), incident IADL (HR 0.80,95%CI [0.70, 0.93]), incident ADL disability (HR 0.80 95%CI [71, 91]) and incident mobility disability (HR 0.81, 95%CI [0.70, 0.93]). Further analyses suggest that grip strength and gait speed rather than muscle mass drive the associations with all four adverse health outcomes. Similar findings were observed when controlling for additional measures used to assess physical frailty including BMI, fatigue and physical activity.

Conclusions

Motor function is the primary driver of the associations of sarcopenia and physical frailty with diverse adverse health outcomes. Further work is needed to identify other facets of muscle structure and motor function which together can identify adults at risk for specific adverse health outcomes.