The Effect of Body Weight on Mortality: Different countries and age groups

The goals of this dissertation were to examine differences in Body mass index (BMI) distribution among Japanese older adults, American older adults, and the U.S. middle-aged; to investigate which factors predict being underweight, overweight or obese among Japanese older adults and American older adults and how weight is associated with chronic diseases and ADL functioning difficulties; to determine how BMI is associated with all-cause mortality in Japanese older adults and the U.S. middle-aged and older adults; to investigate how different levels of BMI are related to all cause mortality and mortality from specific-causes considering the role of biomarkers indicating physiological risk, nutrition, and health behaviors. I found that Japanese older adults (the Nihon University Japanese Longitudinal Study of Aging) have a lower weight distribution with less dispersion than both American middle-aged (the Health and Retirement Study) and older adults (the Longitudinal Study on Aging). Second, education and income did not have an effect on BMI for older men in both countries. However, as years of education increased, both American and Japanese older women are less likely to be overweight. Also, it is interesting that underweight men and women are more likely to have ADL difficulties in the U.S. Third, for total Japanese older adults, being underweight has greater risk of death than being normal weight. For total American older adults, being overweight was associated with a reduced likelihood of dying although most of the indicators of poor health and behaviors are related to being overweight or obese. For American middle-aged persons, overweight or obese people are less likely to die than normal weight. Last, I found that overweight people had significantly higher levels of risk in many biomarkers than normal weight people (the Third National Health and Nutrition Examination Interview Survey). However, underweight people have significantly worse nutritional status and health behaviors than normal weight people. Underweight people who are 65 years and older have an increased hazard of death from all causes and an increased odds of death from cardiovascular disease than normal weight people.

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