Changes in and Interactions between Physical and Mental Health in Older Japanese: The Nakanojo Study

An age-related decrease in functional capacity is consistently reported, but it is not consistently related to a worsening of health-related quality of life (HRQOL) or psychological adjustment. A poor functional capacity and HRQOL have been associated with anxiety or depression, but the possible causal nature and direction of the relationship remain to be explored using long-term longitudinal data.

The purpose of this study was to examine age-related changes in functional capacity, HRQOL, and scores on the Hospital Anxiety and Depression Scale (HADS), and possible causal interrelationships between these variables.

Study participants were 5,124 Japanese aged ≥65 years. After the baseline study (2003), annual follow-up observations continued for 10 years. Generalized linear mixed models examined age-related changes in Barthel index (BI), Tokyo Metropolitan Institute of Gerontology Index of Competence (TMIG-IC), HRQOL, and HADS. Cross-lagged effects models tested possible causal interrelationships.

With age, functional capacity and HRQOL scores showed similar declines in both sexes. Changes in mental health, anxiety, and depression developed more slowly than decreases in physical health (BI, TMIG-IC, and physical functioning scores). Cross-lagged effects models demonstrated that functional capacity had positive effects on psychological adjustment, and that psychological adjustment had positive effects on functional capacity 5 years later. Interactions between functional capacity and psychological adjustment showed no sex differences. A decline in functional capacity negatively affected psychological adjustment, but reduced psychological adjustment had no significant impact on functional capacity 5 and 10 years later. Moreover, functional capacity and poor psychological adjustment showed no interactions in either sex.

Functional capacity and mood state are interrelated. Greater function could sustain vitality and mental health, possibly reducing anxiety and depression.