This study indicated that a higher level, but not a basic level, of health literacy was associated with healthy lifestyle behaviors. Reports have demonstrated an association between health literature and health-related behaviors. Limited health literacy has been shown to be associated with unhealthy lifestyle behaviors [45–48]. Other studies have demonstrated that higher health literacy is related to increased exercise and fruit and vegetable consumption [29, 49, 50]. However, not all studies on health literacy have found such a relationship. Additionally, studies tended to investigate disease populations, such as patients with diabetes, rather than the general population. Showing the association between higher level, not basic level of health literacy, and wide spectrum lifestyle behaviors among people who do not have specific diseases in this study expands the scientific knowledge. In particular, individuals who had gained knowledge and skills of health promotion in line with HJ21 as the target population were directed toward future actions for national health promotion.
While both the EU-HLS-Q47-J and CCHL explained health-related lifestyle behaviors statistically significantly, the NVS-J was not associated with health-related lifestyle behaviors in this study. Various instruments have been developed to improve health literacy. The NVS-J primarily measures the functional level of health literacy, assessing basic reading and writing skills to function effectively in everyday situations. The EU-HLS-Q47-J and CCHL assess more complex health literacy, including communicative and critical health literacy, for practical application in everyday life. Progression from basic and functional health literacy to communicative and critical health literacy requires multiple factors such as advanced cognitive skills, literacy, social and communication capacity, and self-efficacy [26]. Thus, the functional level of health literacy may not be adequate to change behaviors in terms of health. This is supported by the results that only communicative and critical health literacy, but not functional literacy, were associated with health-related lifestyle behaviors in the study.
There are several hypothesized mechanistic links between health literacy and health actions and outcomes in prior studies [51–53]. However, most of these target limited health literacy and patients with certain diseases. None of them provide a clear causal link between health literacy and healthy lifestyle behaviors among populations that are not restricted to narrow disease entities. Baker proposed that health literacy is causally linked to improved health outcomes through several factors, such as new knowledge, positive attitudes, self-efficacy, and behavior change [52]. Paasche-Orlow and Wolf illustrated the causal pathway between limited health literacy and health outcomes, where patient and extrinsic factors—including motivation, self-efficacy, problem-solving skills, resources, and support technology—mediate this relationship [51]. Studies on health literacy interventions reported improved health outcomes. While a causal pathway between health literacy and health-related lifestyle behaviors is needed to determine how and what factors affect the relationship, our finding—that a higher level of health literacy is related to health-related lifestyle behaviors—implies that future interventions should target improvements in levels of health literacy. Whether a functional level of health literacy underpins a higher level of health literacy, and is necessary for acquiring higher levels, is of scientific interest considering effective health literacy interventions for a larger population.
Health literacy seems to be the key target for national health promotion, based on existing evidence and our results. The World Health Organization recognized the efforts to raise health literacy as crucial in the 2030 agenda for sustainable development [54]. Many countries, including Japan, emphasize the importance of health literacy in their action plans for national health promotion in an aging environment [55, 56]. There is ample evidence that a healthy lifestyle prevents many diseases such as obesity, diabetes, cardiovascular disease, stroke, or cancers. In addition to the causal relationship between healthy lifestyle and disease prevention, our finding—that higher health literacy helps people improve health-related lifestyle behaviors—supports the national health promotion program that incorporates health literacy intervention into the core target.
This study has several strengths. First, it measured the different types and categories of health literacy. Many studies have emphasized the importance of the method of health literacy measurement due to lack of robustness in previous health literacy studies [32, 57]. All categories of health literacy, including functional, communicative, and critical health literacy in the study, as well as the different effects on lifestyle, are scientifically important evidence. Second, the measurements are in line with the national health promotion policy, which potentially allows us to apply the effect of health literacy to a large population.
This study has a few limitations as well. First, the sampling method did not involve random sampling of the population. While the study’s participation rate was relatively high (42.4%), convenience sampling, which was used here, does not allow application of the results to the general population. Generalizability to other populations or the general population requires a more robust sampling methodology, which is our future target. Second, the measurements were self-administered and may have included report bias.