Document Type


Date of Degree

Fall 2018

Access Restrictions

Access restricted until 01/31/2021

Degree Name

PhD (Doctor of Philosophy)

Degree In


First Advisor

Wallace, Robert

First Committee Member

Torner, James

Second Committee Member

Bao, Wei

Third Committee Member

Carter, Knute

Fourth Committee Member

Baquero, Barbara


While the role of obesity in health outcomes has been well described, the role of low body mass index (BMI), body weight relative to height, has largely been ignored. Those with low BMI are commonly excluded completely or combined with the normal BMI category in BMI studies. However, there have been some studies indicating poorer health outcomes among those with lower BMI, particularly that of increased risk of mortality. The purpose of this study is to explore the role of low BMI throughout the lifespan.

Data from the Health and Retirement Study was used to evaluate 1) the association between childhood health and socioeconomic status (SES) exposures and low BMI in midlife adulthood, 2) the association between low BMI and health related outcomes in midlife adulthood (ages 50 to 65), and 3) the association between low BMI in midlife and health related outcomes, including mortality, over a longer follow-up (maximum of 20 years). To increase sample size, two low BMI definitions were used: the traditional

Few significant results were found. Low BMI status was consistently associated with older age and female gender as well as current smoking status. Childhood exposure of respiratory disease and greater SES disadvantages was more common among those with low BMI in adulthood. In midlife adulthood, low BMI status was associated with increased difficulties with activities of daily living with either definition of low BMI. Increased risk of fracture was associated with a low BMI definition of <18.5. Increased risk of lung disease and decreased risk of high blood pressure was associated with a low BMI definition of ≤20. An analysis of those 30 years old or older found low BMI to be associated with increased risk of mortality and decreased risk of diabetes regardless of low BMI definition. When low BMI was defined as <18.5, those with low BMI were also more likely to experience difficulty with one or more activities of daily living. When low BMI was defined as ≤20, low BMI status was associated with greater risk of lung disease and decreased risk of high blood pressure.

Further research is needed to fully characterize the role of low BMI on health outcomes as well as the role of SES on low BMI. Additionally, there is a need for greater understanding of the potential biological mechanisms of low BMI for health outcomes. Currently, there are few studies evaluating health outcomes and SES of low BMI. Limiting studies to the extreme upper end of the BMI spectrum limits the overall understanding of the role of BMI in health and may overlook unique characteristics and challenges those with low BMI may face.


BMI, HRS, life-course, underweight


xi, 93 pages


Includes bibliographical references (pages 87-93).


Copyright © 2018 Andrea Lee Holcombe

Available for download on Sunday, January 31, 2021