Cognition Mediates The Relationship Between Sensory Function And Walking Speed In Older Adults

Aim: Walking speed can effectively assess the health status,and declining in walking speed is a risk factor for activities of daily living limitation,falls,disability and mortality in older adults.Evidence from epidemiological studies indicated that sensory function affected walking speed;however,the underlying mechanism is still unclear.The “information-degradation” and “sensory-deprivation” hypothesis clarify from a biological perspective that the association between sensory function and walking speed may be mediated by cognitive.Meanwhile,many observational studies have found that sensory function is linked to cognition,and in turn affects walking speed.However,few observational studies have explored the causal pathways among sensory function,cognition,and walking speed.Here we conducted a cross-sectional study by using a large,population-based sample to assess whether cognitive function may mediate the associations of hearing and vision with gait speed in older adults.Methods: Data were from the English Longitudinal Study of Ageing(ELSA),Wave 7,and we selected the sample of adults aged 60 years and older in this study.Walking speed was assessed by “timed walking test”.Sensory function included vision,hearing,and dual sensory function.Vision was obtained through self-assessment questionnaire survey.Hearing was measured by using a hearing screening device.Dual sensory function was assessed through a comprehensive evaluation of vision and hearing.Participants' cognition were measured using ELSA standardized questionnaires,and included 3 domains,i.e.,memory(immediate and delayed),verbal fluency,and time orientation.Baron and Kenny's causal steps method was used to explore the relationships between sensory function,cognition and walking speed.In addition,we used KHB methods to examine the mediating effect of cognition on the association of sensory function with walking speed.All models were basically adjusted for the potential confounders: age,sex,educational level,cigarette smoking,alcohol drinking,physical activity,cancer,heart attack,hypertension,diabetes,arthritis,osteoporosis and hearing aid.In addition,hearing and vision,as the main independent variables were adjusted mutually in the separate analysis.Results: A total of 7,096 participants aged 60 years or over were included in this study.In this population of community-dwelling older adults,52.5% had poor vision and 59.1% had poor hearing;18.4% had single poor vision,25.9% had single poor hearing and 33.1% had poor dual sensory function.Multiple linear regression and KHB models were used to explore the relationships between sensory function,cognition and walking speed.The results of independent analysis for vision and hearing showed that worse vision(?=-0.052,95%CI:-0.063~-0.037,P<0.001)or hearing(?=-0.053,95%CI:-0.067~-0.039,P<0.001)was associated with slower walking speed;worse vision(?=-2.205,95%CI:-2.637~-1.774,P<0.001)or hearing(?=-1.760,95%CI:-2.231~-1.289,P<0.001)was associated with lower level of global cognition function;after adjusting for all the covariates as well as hearing and vision,the cognition was positively correlated with walking speed(?=0.006,95%CI: 0.006~0.007,P<0.001);after introducing cognition into the models,regression coefficients between vision(?=-0.042,95%CI:-0.054~-0.030,P<0.001),hearing(?=-0.043,95%CI:-0.056~-0.029,P<0.004)and walking speed decreased,indicating the potential mediating effect of cognition on the association between vision,hearing and walking speed;the indirect effect of cognition in the relationship between vision,hearing and walking speed were-0.039 and-0.010,with 23.78% and 19.52% of the total effect being mediated,and the results were statistically significant.The results of combined analysis for vision and hearing found that compared with participants with normal dual sensory function,participants with impaired dual sensory function had slower walking speed(?=-0.028,95%CI:-0.047~-0.008,P=0.005 for single poor vision;?=-0.035,95%CI:-0.053~-0.016,P<0.001 for single hearing and ?=-0.100,95%CI:-0.119~-0.082,P<0.001 for poor dual sensory function);participants with impaired dual sensory function had lower level of cognition(?=-1.530,95%CI:-2.188~-0.873,P<0.001 for single poor vision;?=-1.325,95%CI:-1.954~-0.697,P<0.001 for single hearing and ?=-3.746,95%CI:-4.365~-3.126,P<0.001 for poor dual sensory function);the cognition was positively correlated with walking speed(?=0.006,95%CI: 0.006~0.007,P<0.001);after introducing cognition into the models,regression coefficients between dual sensory function and walking speed decreased(?=-0.019,95%CI:-0.038~ 0.000,P=0.052 single poor vision;?=-0.026,95%CI:-0.044~-0.008,P=0.004 for single hearing and ?=-0.079,95%CI:-0.097~-0.061,P<0.001 for poor dual sensory function),indicating the potential mediating effect of cognition on the association between dual sensory function and walking speed;the indirect effect of cognition in the relationship between single poor vision,single poor hearing and poor dual sensory function walking speed were-0.010,-0.008,-0.022,with 32.33%,22.91%,21.71% of the total effect being mediated,and all the results were statistically significant.Sensitivity analysis results showed that the results of this study were relatively stable and high reliability.Conclusions: This study confirmed that cognitive partially mediates the relationship between sensory function and walking speed,which provides a biological mechanism for studying the relationship between sensory function and walking speed,and also supplies a scientific basis for the formulation of interventions to prevent gait disorder and falls in the elderly.