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Determinants of the population health distribution: an illustration examining body mass index

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posted on 10.10.2019 by David Bann, Emla Fitzsimons, Will Johnson
Most epidemiological studies examine how risk factors relate to average difference in outcomes (linear regression) or odds of a binary outcome (logistic regression); they do not explicitly examine whether risk factors are associated differentially across the distribution of the health outcome investigated. This paper documents a phenomenon found repeatedly in the minority of epidemiological studies which do this (via quantile regression); associations between a range of established risk factors and body mass index (BMI) are progressively stronger in the upper ends of the BMI distribution. In this paper, we document this finding and provide illustrative evidence of it in the 1958 British birth cohort study. Associations of low childhood socioeconomic position, high maternal weight, low childhood general cognition and adult physical inactivity with higher BMI are larger at the upper end of the BMI distribution, on both absolute and relative scales. For example, effect estimates for socioeconomic position and childhood cognition were around three times larger at the 90th compared with 10th quantile, while effect estimates for physical inactivity were increasingly larger from the 50th-90th quantiles, yet null at lower quantiles. We provide potential explanations for these findings and discuss implications. Risk factors may have larger causal effects amongst those in worse health, and these effects may not be discovered when health is only examined in average terms. In such scenarios, population-based approaches to intervention may have larger benefits than anticipated when assuming equivalent benefit across the population.. Further research is needed to understand why effect estimates differ across the BMI outcome distribution and investigate whether differential effects exist for other physical and mental health outcomes.

Funding

Economic and Social Research Council (grant number ES/M001660/1)

Academy of Medical Sciences/the Wellcome Trust “Springboard Health of the public in 2040” Award [HOP001\1025].

Medical Research Council (MRC) New Investigator Research Grant (MR/P023347/1)

History

School

  • Sport, Exercise and Health Sciences

Published in

International Journal of Epidemiology

Volume

49

Issue

3

Pages

731–737

Publisher

Oxford University Press (OUP)

Version

VoR (Version of Record)

Rights holder

© the Authors

Publisher statement

This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted reuse, distribution, and reproduction in any medium, provided the original work is properly cited.

Acceptance date

22/11/2019

Publication date

2020-01-13

Copyright date

2020

ISSN

0300-5771

Language

en

Depositor

Dr Will Johnson

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