Birth Order, Family Size, and Their Association with Obesity and Chronic Disease in U.S. Adults Restricted; Files Only

Abstract

Objective:

This study investigates the association between birth order and family size with chronic diseases, including obesity, in U.S. adults. The relationship between birth order and adult health outcomes is multifactorial and reflects aggregate and accumulative changes in family, behavioral, and environmental factors with increases in family size over time. Studying the impact of birth order and family size on adult health provides valuable insights into whether early-life factors and family dynamics shape long-term health outcomes.

Data Sources/Study Setting:

I used the nationally representative, cross-sectional data from the 2021 Panel Study of Income Dynamics (PSID) survey, to analyze 1,543 adults with biological siblings and 740 adults who were only children, all aged 20+ years in 2021.

Study Design:

I examined associations between birth order and: obesity and the presence of 1+disease among type-2-diabetes, hypertension, or heart disease. Fixed effects models adjusted for age and sex were used to analyze the differences in outcomes among siblings within families; and survey weighted linear probabilities regression models adjusted for age, sex, race/ethnicity, and income was used for analyses comparing only-children and first-borns with siblings.

Principal Findings:

Second or later-born adults were significantly less likely to have obesity (5.13% point) and to have at least one chronic disease (5.32% point) compared to first-born adults. Only-children were not significantly different in the probability of obesity or chronic disease.

Conclusions:

Birth order is associated with adult health outcomes, with later-born adults exhibiting lower likelihood of obesity and chronic diseases compared to first born individuals in adulthood. This could be attributed to a number of early life factors such as prenatal nutrition, parental attention and investment, and other factors over the course of their lives such as behavioral and environmental factors that contribute to chronic stress. While only-children were not significantly different compared to first-born adults with siblings, this null effect could be attributed to one or a combination of the following: a true null finding where only-children and first-born adults face the same odds of obesity and chronic disease, a limitation of the modest sample size, or the interplay of various health protective and risk factors over the course of their lives that potentially counter each other’s effects.

Table of Contents

Contents

Chapter I. Introduction .................................................................................................... 1

Chapter II. Background and Literature Review ................................................................... 2

Obesity and chronic disease among U.S. adults ............................................................... 2

Implications of birth order ............................................................................................ 3

Importance of studying birth order effects on adult health outcomes ................................... 4

Current literature and gaps............................................................................................ 5

Main research questions ............................................................................................... 6

Chapter III. Methodology ................................................................................................ 7

Conceptual framework ................................................................................................. 7

Focal relationship 1 ..................................................................................................... 8

Mediators and causal pathways ..................................................................................... 9

Moderators/cumulative inputs ..................................................................................... 11

Other factors: ........................................................................................................... 12

Focal relationship 2 ................................................................................................... 14

Mediators and causal pathways: .................................................................................. 16

Early life inputs/exposures: ........................................................................................ 17

Testable hypotheses ................................................................................................... 19

Data ........................................................................................................................ 20

Analytic sample derivation ......................................................................................... 21

Outcomes and covariates ............................................................................................ 22

Analytic plan ............................................................................................................ 26

Chapter IV. Results ....................................................................................................... 29

Descriptive statistics .................................................................................................. 29

Model A results ......................................................................................................... 31

Results summary: Model A ..................................................................................... 31

Model B results ........................................................................................................ 33

Results summary: Model B ..................................................................................... 34

Sensitivity analysis .................................................................................................... 34

viii

Chapter V. Discussion ................................................................................................... 37

Mechanisms ............................................................................................................. 40

Implications ............................................................................................................. 41

Study strengths and limitations .................................................................................... 41

Future direction ........................................................................................................ 42

Conclusion ............................................................................................................... 43

References................................................................................................................... 44

Appendix .................................................................................................................... 51

About this Master's Thesis

Rights statement

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School	Rollins School of Public Health
Department	Health Policy and Management
Degree	M.S.P.H.
Submission	Master's Thesis
Language	English
Research Field	Health Sciences, Public Health
关键词	Birth order Obesity Life course health development Developmental origins of disease Chronic disease
Committee Chair / Thesis Advisor	Chehal, Puneet Kaur, Emory University
Committee Members	Huang, Ying, University of Texas at San Antonio Cunningham, Solveig Argeseanu, Emory University

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