Smartphones are essential in mobile health, especially for older people, by offering a cost-effective approach to self-monitoring and managing chronic diseases at home through built-in functions.1 Despite a lower smartphone usage rate among older people compared to younger people, smartphone usage among older people has increased rapidly worldwide. One of the reasons for this may be that the functions and apps built into smartphones have the potential to meet the various health and well-being needs of older people.2

Several studies have reported that older people's smartphone usage can increase social participation, reduce loneliness, improve access to new information, and improve life satisfaction.3,4 Life satisfaction, a crucial aspect of subjective well-being among older people, encompasses the perception of the quality of various dimensions of their lives including health status, housing, finances, leisure activities, and relationships with family, friends, and neighbors.5,6 It was reported that life satisfaction was closely associated with psychological health, including depressive symptoms and cognitive function.7

Depressive symptoms and cognitive function exhibit a close relationship, as shown by previous longitudinal studies revealing that depressive symptoms influence cognitive decline.8, 9, 10 Additionally, smartphone usage is positively associated with a reduction in depressive symptoms,11 and it helps improve cognitive function among older people with and without cognitive decline.12,13 According to the findings of previous studies indicating that depressive symptoms and cognitive function have been shown to mediate the relationship between other factors and life satisfaction, this can be extended to the association between life satisfaction and depressive symptoms and cognitive function.14, 15, 16

However, previous studies have demonstrated fragmentary relationships among smartphone usage, depressive symptoms, cognitive function, and life satisfaction. Few studies have investigated the complex relationships between these concepts. Therefore, this study aimed to explore life satisfaction based on the status of smartphone usage and the mediating effects of depressive symptoms and cognitive function on the relationship between smartphone usage and life satisfaction in older people. Additionally, this study attempted to conduct a sub-analysis to investigate the mediating effects of depressive symptoms and cognitive function on the relationship between smartphone usage level and the life satisfaction of smartphone users included in this study. Each hypothesis (H) of this study was as follows (Fig. 1):

H 1

The status of smartphone usage contributed to lower depressive symptoms and higher cognitive function, which subsequently led to improved life satisfaction (main analysis).

H 2

The level of smartphone usage contributed to lower depressive symptoms and higher cognitive function, which subsequently led to improved life satisfaction (sub-analysis).