Midlife Predictors of Old Age Functioning: Insights from Longitudinal Cohort Studies

Addressing the challenges posed by aging populations is a primary focus of publichealth efforts worldwide. Central to this effort is the enhancement of functionalability among older adults, as good functional ability promotes maintainingindependence, autonomy, and a high quality of life. Moreover, supporting healthyaging not only benefits individuals and communities but also carries profoundimplications for the demands placed on social and healthcare systems.The process of developing and maintaining functional ability throughout olderage is influenced by various factors experienced across one's lifetime. This studyseeks to contribute to the understanding of these factors. Through the adoption ofa life course perspective, the aim is to investigate the effects of mid-life predictors,including education level, occupational physical activity, and the presence of lowback pain on functioning in old age. Instead of a single-point assessment, this studyincorporates the developmental trajectories of low back pain and occupationalphysical activity from mid-working life to retirement, providing a broader history ofexposure to these factors. Furthermore, the mechanisms through which educationalattainment influences functioning are investigated.This study utilizes data from three different cohort studies that have trackedindividuals from their mid-working years to old age. These cohorts include theFinnish Health 2000 and 2011 Studies (with an 11-year follow-up period), theFinnish Longitudinal Study of Ageing Municipality Employees (FLAME) (spanningfrom 1981 to 2009), and the Health and Retirement Study (HRS) in the USA(covering the period from 1992 to 2016). At baseline, the participants included inthe analysis were aged 55 years and older in the Finnish 2000 Study, 44 to 58 yearsin FLAME, and 50 and older in the HRS.The overall outcome of the study, functioning, comprises both objectivelymeasured and self-reported data. In Study I, the maximum walking speed of Finnisholder adults aged 55 years and older was measured at baseline and again at an 11-year follow-up. The outcome variable, the decline in maximum walking speed, wascalculated as the difference between these two measurements. In Studies II and III,the outcome variables were self-reported mobility limitations and disability. Theseoutcomes were assessed 28 years after the baseline in FLAME (in 2009) and 24 yearsviiiafter the baseline in HRS (in 2016). The outcomes were assessed with self-reportedlimitations in walking and stair climbing collected through questionnaires (FLAME)or phone interviews (HRS). Any level of difficulty was considered as having mobilitylimitations. Similarly, any level of difficulty in performing basic activities of dailyliving was considered as having a disability. Data on the main predictors (educationlevel, occupational physical activity, and low back pain), and the covariates werecollected through questionnaires (Finnish Health 2000 Study and FLAME) orinterviews (HRS).Study I focused on educational disparities in walking speed decline over an 11-year follow-up among Finnish general population aged 55 years and older. Generallinear model was employed to investigate variations in the decline of maximumwalking speed across different education groups. Mediation analyses, utilizing theproduct method, were carried out to dissect the overall effect of education on thedecline in maximum walking speed into direct and indirect effects mediated throughintermediaries. The findings indicated that lower education levels were associatedwith a more rapid decline in maximum walking speed, with the differences betweeneducation groups widening as individuals aged. Additionally, the results indicatedthat higher lifetime exposure to physical workload and higher body mass indexamong individuals with lower education levels contributed significantly to theeducational differences observed in mobility decline.The results of Study II also underscore the role of midlife physical workload inincreasing the risk of functional limitations in old age. The study investigated thedevelopmental profiles of occupational physical activity in Finnish and U.S. agingworkers, and their associations with mobility limitations and disability two decadeslater. Repeated measurements of self-reported occupational physical activity werecollected during approximately an 11–12-year period using harmonized data fromFLAME and HRS. Latent class growth analysis was used to identify the profiles, andrisk ratios with 95% confidence intervals for the associations of the profiles and laterlife mobility limitations and disability were estimated using Poisson loglinearregression analyses. The results showed that perceived occupational physical activityremained relatively stable among the workers during the follow-up, particularlyamong workers reporting high or low occupational physical activity at baseline,whereas people reporting moderate level occupational physical activity had higherfluctuation in their exposure level. Notably, consistently high occupational physicalactivity significantly increased the risk of self-reported mobility limitations in old age.In Study III, low back pain emerged as another crucial determinant of old agefunctioning. Using data from FLAME, the study investigated low back painixtrajectories from midlife to retirement among Finnish municipal workers, and theassociation of these trajectories with mobility limitations and disability at old age.Latent class growth analysis was used to identify the low back pain trajectories andadjusted logistic regression analysis to investigate the associations of the derived LBPtrajectories with the outcomes. The results showed three distinct trajectories of lowback pain: high-decreasing, intermediate-stable, and low. Members of the highdecreasing and the intermediate-stable trajectories exhibited markedly more mobilitylimitations and disability in old age compared with those in the low trajectory.Moreover, individuals working in physically demanding occupations (“blue-collar”workers) were more likely to belong to the high-decreasing low back pain trajectorythan those working in physically lighter occupations, suggesting that low back painmay be an important mediator between physical workload and late-life functionallimitations.In summary, the results of the study showed that all the investigated mid-lifepredictors - educational level, occupational physical activity, and presence of lowback pain, were significantly associated with old age functioning, thus highlightingtheir importance for healthy aging. This study pinpointed several modifiable riskfactors acting during a sensitive period spanning from mid-working life to old agethat profoundly impact functioning beyond retirement. The research underscoresthe importance of mitigating physical work demands, in particular among lesseducated individuals, and managing mid-life low back pain to enhance functionalability and ensure quality of life in old age. These insights contribute tounderstanding the sensitive period in late working life as pivotal for interventionsaimed at supporting sustained functional independence among the aging population.