This study examined the 1-year incidence and persistent prevalence of MetS among the nationwide screening program during the fiscal year of 2008 to 2014 (6 years). As a whole, the 1-year incidence was 9.6% in men and 3.5% in women, and the persistent prevalence of MetS was 49.6% in men and 43.3% in women, respectively. Significant differences in sex and age group were evident in both the 1-year incidence and persistent prevalence of MetS. Men and the elderly group (age≥65) population were at risk of higher 1-year incidence and persistent prevalence of MetS. According to the abridged life table from the Ministry of Health, Labour and Welfare, the life expectancy was78.4 years in men and 85.3 years in women in 2002, and it increases to 81.4 in men and 87.5 years in 2019, respectively. The gender discrepancy of life expectancy remains high at 6 years, yet the reasons are not clear.
Subjects with MetS have a significant impact on the incidence of CKD2, 3, 4, diabetes mellitus (DM)5, 6, and mortality7-10. Accordingly, when diagnosed MetS, they are entitled to further examination and lifestyle intervention. Lifestyle per se is a significant modifier of CKD11, CVD12, and mortality12-13. Recently, we confirmed that MetS was a significant risk factor of mortality14. Therefore, early intervention in overweight/obese adults, namely MetS subjects is necessary to prevent the progression of CKD16, 17 and death.
The dipstick proteinuria test for CKD detection was shown to be cost-effective18, 19, however not yet shown for the diagnosis of MetS at the general screening. The key strategy for the prevention of MetS is to keep body weight within the normal range by nutritional management and adequate exercise. in particular aged populations. Intervention through this screening program was shown to be very effective for the reversal of MetS15. However, the proportion of people attending the program as low as 11%. The trends in the 1-year incidence and persistent prevalence of MetS have not been well studied. Such information would be helpful for the future modification of the protocol of screening among the Japanese population.
Lifestyle modification if convinced by the screened participants would prevent the overall incidence of MetS and reduce the prevalence of MetS. Other than the weight reduction in overweight and obese subjects, excess alcohol intake, in particular, men, is frequently observed with MetS. Alkerwi A et al recommended restricting alcohol consumption of less than 20 g/day among women, and of less than 40 g/day among men20. Other lifestyles such as depression21 and self-reported sleep duration22 are reported to the associated with MetS. These observations need to be confirmed among the Japanese but are suggesting the importance of further questionnaires among apparently healthy people.
MetS were defined as waist circumference (men≥85cm, women≥90cm) plus two or three abnormal values in blood sugar metabolism, lipid, and blood pressure14. Waist circumference is a surrogate of central obesity but is often variable by body size, gender, and race. We reported the significance of “a body shape index (ABSI)” on all-cause mortality among screened subjects10. ABSI seemed to be a better predictor of death than that of the body mass index (BMI). However, the presence of CKD affected differently on mortality between men and women.
Strengths and limitations
The strength of the present study is that we have followed a large number of participants of the nationwide screening program. We believe that this cohort represents the currently available database for the analysis of the changes in MetS status in Japan.
There are several limitations in the present study. First, participants in this analysis were those who had an interest in lifestyle and their health condition. The participation rate was 38.9% (2008) and 51.4% (2016) of the target population. (Ministry of Health, Labour and Welfare) Therefore, it would not be representative of the whole Japanese population. We have no data on whether the MetS (+) individuals had attended the intervention program or not. A previous study showed that men and relatively younger (age<65 years) had a lower participation rate compared to their counterparts19. Second, other socio-economic factors related to the incidence and prevalence of MetS are unknown in this screening program. The number of family members, the presence of a spouse, and the location of residence might influence the lifestyle. Third, factors other than the differences in lifestyles and history of CVD, stroke, and renal failure at baseline may explain the results of the present study. Long-term lifestyle would be difficult to change by single intervention, in a particular elderly population. Fourth, we have no data of those aged 75 and over. The medical care system for the elderly in the later stage of life has also started in 2009 in Japan. Further studies on transition to this program may be warranted. Finally, other limitations on the diagnosis of MetS have been discussed in the previous paper14.