Age and gender differences in the association between body mass index and all-cause mortality among older Japanese

Archived Abstract of Former PSC Researcher

Murayama, Hiroshi, Jersey Liang, Benjamin A. Shaw, Anda Botoseneanu, Erika Kobayashi, Taro Fukaya, and Shoji Shinkai. 2018. "Age and gender differences in the association between body mass index and all-cause mortality among older Japanese." Ethnicity & Health, 0(0): 1-14.

Objective: Increasing evidence suggests a reverse J-shaped association between body mass index (BMI) and all-cause mortality among the older population. However, findings from non-Western societies including Japan are still sparse. Furthermore, little evidence regarding variation by age and gender in the BMI-mortality relationship in old age exists. This study aimed to examine age and gender variations in the relationship between BMI and all-cause mortality among older Japanese.Design: Data came from a national representative sample of community-dwelling Japanese aged 60 years and older at baseline (n = 4,869). Participants were followed for up to 25 years. We categorized BMI into seven categories: < 18.5, 18.5-19.9, 20.0-21.4, 21.5-22.9, 23.0-24.9, 25.0-26.9, and ≥ 27.0. Cox proportional hazards models were used to assess the relative mortality risk associated with BMI categories.

Results: Lower BMI (< 18.5 and 18.5-19.9) was associated with higher mortality, compared to the mid-normal weight category (BMI: 21.5-22.9), after adjusting for covariates. In contrast, high-normal weight (BMI: 23.0-24.9) and overweight (BMI: 25.0-26.9 and ≥ 27.0) were not associated with mortality. Relative to old-old (aged ≥ 75 years), the higher mortality risk associated with lower BMI (< 20) appeared to be more prominent among young-old (aged 60-74 years). A moderately increased mortality risk associated with low BMI (18.5-19.9) was identified among men but not among women.

Conclusion: Among older Japanese, low BMI (< 20.0) was associated with higher mortality, while high BMI (≥ 27.0) was not. The increased mortality risk associated with low BMI is more apparent among young-old and men. These age and gender differences need to be considered in assessing healthy body weight in old age.

10.1080/13557858.2018.1469737

Keywords:
Japan older adults mortality Body mass index effect modification

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