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Date
Jun
06
2006

Is Being Overweight A Big Deal? Body Mass Index and Health Dynamics of Elderly Americans

Presenter:

Zhou Yang

Authors:

Zhou Yang

Chair: Don Kenkel; Discussant: TBA Tue June 6, 2006 15:30-17:00 Room 121

Abstract

There is much debate about whether being overweight is a serious concern of the health among American people recently. Up to the end of 1990s the general conclusion is the relationship between Body Mass Index (BMI) and mortality rate from all reasons is in a concave shape where the highest and lowest mortality rates are observed among people in the lowest and highest BMI level, and the optimal weight associated with lowest mortality rate was determined to be between 23.5 to 24.9 in men, and between 22.0 and 23.4 in women.

However, there has been much debate recently concerning the health risk related to obesity. The center of the debate is the publication on JAMA (Flegal et al.. ,2005 ) This study shows that the relative risk of death among obese people with BMI 30 or higher is significantly higher than the normal weight people (BMI 18.5 to 25), but the relative risk of death of overweight people with BMI between 25 and 30 is the same as the normal weight people. Other researchers questioned the results and methods of Flegal’s research, and specifically pointed out that the relationship between BMI and mortality is complicated with smoking, chronic diseases and natural aging process which involves loss of bone density and muscularity, and calls for longitudinal behavior research that could investigate the changes in weight, health care behaviors and health outcomes.

This study used a dynamic behavior model to explain that weight is a choice variable of each individual that relates to her health status, health care services consumption, personal habit, and life expectancy. At the same time, weight itself changes over time in a dynamic pattern.

A jointly estimated equation system is then developed based on the theoretical framework to estimate different aspects of dynamic changes of weight and health conditions. Longitudinal data of Medicare Current Beneficiary Survey from 1992 to 1998 was used in the empirical estimation. Discrete random error term was adopted in the maximum likelihood estimation to control for unobserved individual heterogeneity. Both a short-term simulation over the entire sample over 5 year, and a long-term simulation over 35 years on one cohort from 65 were conducted. The results showed that the econometric tools adopted in this study significantly controlled the possible estimation bias caused by unobserved individual heterogeneity. The highest mortality rate is observed among the obese and underweight cohort. The elderly who are overweight does experience higher mortality than the normal weight cohort. Survivors in all age of both the obese and overweight cohort have higher disability rate than the normal weight group. The average weight among the survivors in all age cohorts converge to BMI 24 over time. The obese cohort experienced the worse health outcomes, but highest health care expenditures in total, while the normal weight cohort have the best health and lowest health care expenditures. The optimal weight for the elderly is still suggested to be lower than, and close to 25 up to age 65 in this study.

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