The relationship between healthy life expectancy and smoking, hypertension and body mass index in a Japanese population: A multistate life table method using Nippon Data90

Abstract

Introduction Healthy life expectancy (HLE) is an important measure for describing population health. Human factors such as smoking, hypertension, and obesity can reduce overall HLE in a population. Little is known about the relationship between HLE and cardiovascular risk factors in Asian populations. Our study aimed to estimate HLE in various combinations of cardiovascular risk factors in a Japanese population using a multistate life table approach. Methods Data were obtained from NIPPON DATA90, which is a nationwide cohort study of nine thousand Japanese people that was established in 1990. From among the NIPPON DATA90 participants, our analysis focused on people who were aged 60 years or older at the baseline survey and had received activities of daily living (ADL) assessment. Participants underwent a two-wave interview survey process using the Katz ADL index in 1995 and 2000. The participants were queried on five items of the Katz ADL index, and any participant who answered that they were “not independent” for at least one item was designated “disabled” in the multistate life table. Smoking status was categorized into non-smokers (never-/ex-smokers) and current smokers. Blood pressure (BP) was categorized into four groups (optimal, normal, stage 1 hypertension, and stage 2 hypertension). Obesity was defined using body mass index (BMI), which was categorized into three groups (thin: 18.5; normal: 18.5–24.9; and overweight/obese: ≥ 25). All HLE calculations were performed using iMaCh version 0.98r7 (A Maximum Likelihood Computer Program using Interpolation of Markov Chains). Results The study sample comprised 6676 participants (2840 men and 3836 women). Among all the BMI and BP groups, HLE at age 60 in current smokers was shorter than that of non-smokers. Among obese men with optimal BP, HLE in current smokers was 20.0 years, whereas that of non-smokers was 17.7 years. Among obese current smokers, HLE at age 60 decreased linearly as BP increased in men (optimal BP: 19.8 years, normal BP: 19.3 years, stage 1 hypertension: 18.1 years, stage 2 hypertension: 17.7 years) and women (optimal BP: 23.1 years, normal BP: 22.6 years, stage 1 hypertension: 21.4 years, stage 2 hypertension: 21.0 years). Among thin current smokers, HLE at age 60 also decreased linearly as BP increased in men (optimal BP: 18.3 years, normal BP: 17.8 years, stage 1 hypertension: 16.6 years, stage 2 hypertension: 16.3 years) and women (optimal BP: 21.8 years, normal BP: 21.2 years, stage 1 hypertension: 19.9 years, stage 2 hypertension: 19.6 years). The distribution of HLE at age 60 showed a slight inverted U-shape as BMI increased in both sexes. Conclusions We examined the relationship between HLE at age 60 and combinations of BMI, BP, and smoking status using a nationwide cohort study of the Japanese population. HLE at age 60 was clearly shorter in smokers and individuals with higher BP. Furthermore, both thin and obesity has a slight impact on HLE at age 60.