Metabolic syndrome, which is characterized by excess abdominal fat, elevated blood pressure, abnormal cholesterol levels, and high blood sugar, has become a significant public health concern. This condition significantly increases the risk of cardiovascular events, as indicated in several studies (Zimmet et al., 2005; Grundy, 2006; Kaur, 2014; Grundy, 2016). Nevertheless the proportion of obese individuals is low in Japan compared to international figures, the number of obese men is increasing annually, thereby amplifying the risk of cardiovascular event (Japan National Health and Nutrition Survey, 2019). In response, the Japanese healthcare system has implemented Specific Health Checkup and Specific Health Guidance programs since 2008 (Kohro et al., 2008). These programs target early detection and intervention for individuals at risk, focusing particularly on metabolic syndrome and visceral fat obesity. Aimed at insured individuals and dependents aged 40 to 74, they are pivotal in preventing and improving lifestyle-related diseases. The programs include comprehensive physical examinations to identify individuals needing health guidance, followed by professional lifestyle modification advice for those at risk of metabolic syndrome.

Recently, Tsushita et al. and Nakao et al. assessed the obesity measurements and other cardiovascular risk factors differences between participants and nonparticipants eligible for Specific Health Guidance (Tsushita et al., 2018; Nakao et al., 2018). Their results showed significantly greater improvements in obesity and other risk factors of the cardiovascular event among participants. However, concerns about bias from unobserved confounders and self-selection in participation persist when comparing populations with and without guidance participation. To mitigate these biases, Fukuma et al. and Sekizawa et al. used a quasi-experimental regression discontinuity design, comparing the obesity level and risk factor changes between individuals with and without a greater obesity level than the criteria threshold. Their study suggested that eligibility for guidance modestly reduces obesity, but might not improve other cardiovascular risk factors (Fukuma et al., 2020; Sekizawa, 2023).

The previous studies have evaluated the relationship between guidance interventions and individual cardiovascular risk factors, and there is limited evidence to show that guidance has an impact on actual cardiovascular events. This may be due to the challenge of using actual diagnostic information in studies involving healthy participants. To overcome this issue, we utilized the predictive comprehensive risk consisting of multiple individual risk factors instead of the actual diagnostic information. Furthermore, the previous studies focused on the changes in cardiovascular risk factors after the checkup and guidance; and the estimates of the intervention effects may include bias when the trends before the checkup and guidance vary between the comparison groups. To consider the pre-intervention trends in the estimation, as well as the effect of self-selection of the intervention, our study employed an Interrupted Time Series (ITS) design. In the ITS design, we assessed the trends of the outcomes over time and the change in trends before and after the intervention among individuals who participated in the guidance (Bernal et al., 2017; Wagner et al., 2002; Hategeka et al., 2020). The ITS design is one of the strongest quasi-experimental designs used to accurately estimate the impact of the introduction of an intervention.

In this study, we aimed to examine whether the intervention of Specific Health Guidance mitigates the escalation of the predicted risk of cardiovascular events and its components in Japanese working-age individuals.