We found that the higher half of the clustered health-related lifestyle score group showed a statistically significant higher purpose in life than the lower half of the clustered health-related lifestyle score group. The study also highlighted a significant positive association between the clustered health-related lifestyle score and the Ikigai-9 score. To the best of our knowledge, this study was the first to show that a strong sense of purpose in life correlates with clustered health-related lifestyles in the context of a national health campaign. Several studies indicated a positive relationship between purpose in life and health-related lifestyles [1,23-25]. Also, many publications revealed a correlation between a single healthy habit and purpose in life. Therefore, our findings, affirming a positive relationship between purpose in life and clustered health-related lifestyle, were consistent with previously reported results and help broaden the evidence of this association.
Exploring the mechanistic link of purpose in life with a healthy lifestyle may help us understand this relationship. While studies have highlighted the positive relationship between purpose in life and health-related lifestyle, a few studies’ results are inconsistent with our findings. For example, a prospective study did not observe a positive association between purpose in life and healthy sleep patterns . In other studies, the purpose of life was not associated with smoking [27,28]. Notably, the mechanistic link between health-related lifestyle and purpose in life was not well examined. Hooker et al. proposed a hypothesized model linking between purpose in life and health . They summarized the relationship between life purpose and health outcomes utilizing the concept of self-regulation. In the model, they proposed that purpose influenced health through three self-regulatory processes and skills: stress-buffering, adaptive coping, and health behaviors. Health-related lifestyle, one of the self-regulatory processes, is the result of individuals setting goals, monitoring their progress, and using feedback to modify their lifestyle . Thus, a purpose provides a foundation and motivation for engaging in a healthy lifestyle. Kim et al. also suggested that sense of purpose in life enhances the likelihood for engagement in restorative health-related lifestyle practices (e.g., physical activity, healthy sleep quality, use of preventive health care services) from cardiovascular disease to the indirect effect of behavior .
There is an alternative explanation for the mechanistic link between purpose in life and health-related lifestyle. A reverse causality model also suggested that engaging in healthy lifestyle practices could predict a greater purpose in life [29,31]. Our results denoted that the group with a higher score in purpose in life performed healthier lifestyle practices and behaviors (Table 2), which can be supported by either of the hypothesized models. However, further research is needed to clarify the mechanism and the directionality of the association. The mechanism to explain the causal relationship between life purpose and healthy lifestyle practices helped prepare for healthy aging by preventing diseases, increasing health longevity, and imbuing a health-oriented drive, which are the major goals of the HJ21.
Additionally, the difference in life purpose scores between the two groups (35.3 vs 31.4) shown in Table 2 should be further explored, whilst we found a statistically significant difference and a correlation between healthy lifestyle practices and purpose in life. Rather than being a single concept, purpose in life has several elements and a more comprehensive construct. The majority of measurement tools concerned with purpose in life assess two distinct concepts: the subjective presence of meaning (purpose) and subjective search for meaning (purpose) . Ikigai-9 used in this study has three constructs in the measurement of purpose in life and seems to measure both concepts, but the total score does not distinguish between the association of specific constructs and healthy lifestyle practices. Thus, further methodological sophistication regarding the evaluation of a specific concept encompassed within life purpose needs to be studied. This aspect broadens our understanding of purpose in life and its relation to health. This particular cohort of certified specialists shared many features of high health literacy through the process of professional development and certification combined with life-long learning and activities related to their role health management specialists. Health-related lifestyle practices that the certified specialists were far healthier than the national average. These characters entailed health literacy. Health literacy is considered to represent individuals’ capacity to obtain and understand basic health information and services, and to make appropriate health-related decisions based on this information . Therefore, health literacy is directly associated with disease mortality , overall health status , disease prevention [36,37], as well as health behaviors. These can be attributed to purpose in life .
Thus, both health literacy and health-related lifestyle appear to have a similar relationship with disease prevention and better health outcomes. The mediating effect of health literacy on the relationship between healthy lifestyle and life purpose should be investigated. Such inquiries in a prospective cohort study can better explain the mechanism of the causal link between purpose in life, health-related lifestyle, and health literacy.
There are several limitations to the study. First, all the measurements were self-reported, which can be a source of bias. Second, the real-life meaning of purpose in life has not been determined yet. The Ikigai-9 score, one of the tools used to measure the life purpose score, is validated in a small and a limited population; however, the instrument may not capture it holistically. This limitation was implicated by the previously reported systematic review. Furthermore, Zheng et al. found variability in the strength of correlation among the questionnaire for quality of life, part of which included questions regarding a purposeful life . Lastly, the correlational analysis did not include an adjustment for confounding factors other than age. Hence, little is known about factors influencing the relationship between a healthy lifestyle and purpose in life. We need to establish other potential influencing factors and determine which variables have mediating, moderating, and confounding effects on purpose in life to understand the causal relationship between healthy lifestyle practices and life purpose . This exploration proposes a promising model for future intervention programs.
Despite these limitations, this study has several strengths. First, the study sample size, N = 4820, was large and distributed throughout Japan. This aspect of the study increases generalizability. According to the previous review, numerous studies on purpose in life focused on older adults , whereas only a few were concerned with early or middle-aged adults. In the present study, the majority of the study participants were early and middle-aged adults. Second, previous studies used relatively simple questions or did not employ validated tools to measure purpose in life. However, we used a validated tool, Ikigai-9, in this study. This aspect allows the study results to increase the reliability and validity of the measurement of purpose in life and also hold applicability in other studies. Lastly, study participants were certified specialists in health management who have shown high health literacy. This inclusion criterion provides guidance on improving healthy lifestyle practices through health literacy as an approach to health promotion.