Kuo Hsu-Ko, Leveille Suzanne G, Yu Yau-Hua, Milberg William P
Division of Gerontology Research, National Health Research Institutes, Taipei, Taiwan, ROC.
Gerontology. 2007;53(2):102-10. doi: 10.1159/000096792. Epub 2006 Nov 6.
Both cognitive function and gait speed are important correlates of disability. However, little is known about the combined effect of cognitive function and gait speed on multiple domains of disability as well as about the role of gait speed in the association between cognitive function and late-life disability.
To investigate (1) how cognition and habitual gait speed are related to late-life disability; (2) the role of habitual gait speed in the cognitiondisability association; and (3) the combined effect of cognitive function and habitual gait speed on late-life disability.
Participants (>60 years, n = 2,481) were from the National Health and Nutrition Examination Survey 1999-2002. Disability in activities of daily living (ADL), instrumental ADL (IADL), leisure and social activities (LSA), and lower extremity mobility (LEM) was obtained by self-report. Cognitive function was measured by a 2-min timed Digit Symbol Substitution Test (DSST), an executive function measure from the Wechsler Adult Intelligence Test. Habitual gait speed was obtained from a 20-foot timed walk. Multiple logistic regression was used to assess the association between cognitive function and disability.
Cognitive function was associated with decreased likelihood for disability in each domain. The odds ratios (ORs) for disability in ADL, IADL, LSA, and LEM for each standard deviation (SD) increase in the DSST score were 0.47 (95% confidence interval [CI] = 0.34-0.64), 0.53 (95% CI = 0.42-0.67), 0.61 (95% CI = 0.47-0.79), and 0.73 (95% CI = 0.61-0.86), respectively, in the multi-variable models. After additional adjustment for habitual gait speed in the cognition-disability relationship, DSST score was no longer a significant correlate for LSA and LEM disability. The strength of the association between DSST score and disability in ADL/IADL was also diminished. The attenuated association between cognition and disability implies that limitation in gait speed likely mediates the association between cognitive function and disability. We found additive effects of cognition and habitual gait speed on late-life disability. The OR of disability in respective domains were lowest among participants with high-DSST score (high executive function) and with high gait speed. In contrast, the OR tended to be highest among participants with low-DSST score (low executive function) and low gait speed.
Cognitive function was associated with multiple domains of disability. There was a joint effect of cognitive function and gait speed on late-life disability. This study also suggested that habitual gait speed partially mediated the inverse association between cognitive function and late-life disability, providing a mechanistic explanation in the context of disablement process.
认知功能和步速都是残疾的重要相关因素。然而，关于认知功能和步速对残疾多个领域的综合影响，以及步速在认知功能与晚年残疾关联中的作用，我们知之甚少。
探讨（1）认知与习惯性步速如何与晚年残疾相关；（2）习惯性步速在认知与残疾关联中的作用；（3）认知功能和习惯性步速对晚年残疾的综合影响。
参与者（年龄>60岁，n = 2481）来自1999 - 2002年国家健康与营养检查调查。通过自我报告获取日常生活活动（ADL）、工具性ADL（IADL）、休闲和社交活动（LSA）以及下肢活动能力（LEM）方面的残疾情况。认知功能通过2分钟定时数字符号替换测验（DSST）进行测量，这是韦氏成人智力量表中的一项执行功能测量指标。习惯性步速通过20英尺定时步行获得。采用多元逻辑回归评估认知功能与残疾之间的关联。
认知功能与各领域残疾可能性降低相关。在多变量模型中，DSST分数每增加一个标准差（SD），ADL、IADL、LSA和LEM残疾的优势比（OR）分别为0.47（95%置信区间[CI]=0.34 - 0.64）、0.53（95%CI = 0.42 - 0.67）、0.61（95%CI = 0.47 - 0.79）和0.73（95%CI = 0.61 - 0.86）。在认知与残疾关系中进一步调整习惯性步速后，DSST分数不再是LSA和LEM残疾的显著相关因素。DSST分数与ADL/IADL残疾之间关联的强度也有所减弱。认知与残疾之间减弱的关联意味着步速受限可能介导了认知功能与残疾之间的关联。我们发现认知和习惯性步速对晚年残疾有累加效应。在DSST分数高（执行功能高）且步速快的参与者中，各领域残疾的OR最低。相比之下，在DSST分数低（执行功能低）且步速慢的参与者中OR往往最高。
认知功能与多个残疾领域相关。认知功能和步速对晚年残疾有联合作用。本研究还表明，习惯性步速部分介导了认知功能与晚年残疾之间的负向关联，为残疾过程提供了一种机制性解释。
