Toggle Main Menu Toggle Search

Open Access padlockePrints

Adult obesity and mid-life physical functioning in two British birth cohorts: Investigating the mediating role of physical inactivity

Lookup NU author(s): Professor Rachel CooperORCiD



This work is licensed under a Creative Commons Attribution 4.0 International License (CC BY 4.0).


© The Author(s) 2020.Background: Associations between obesity and physical inactivity are bi-directional. Both are associated with physical functioning (PF, ability to perform physical tasks of daily living) but whether obesity influences PF via inactivity is unknown. We investigated whether mid-adult obesity trajectories were associated with subsequent PF and mediated by inactivity. Methods: Body mass index (BMI; kg/m2) and inactivity were recorded at: 36, 43, 53 and 60-64 years in the 1946 Medical Research Council (MRC) National Survey of Health and Development (1946-NSHD; n=2427), and at 33, 42 and 50 years in the 1958 National Child Development Study (1958-NCDS; n=8674). Poor PF was defined as the lowest (gender and cohort-specific) 10% on the Short-form 36 Physical Component Summary subscale at 60-64 years (1946-NSHD) and 50 years (1958-NCDS). Estimated randomizedinterventional- analogue natural direct (rNDE) and indirect (rNIE) effects of obesity trajectories on PF via inactivity are expressed as risk ratios [overall total effect (rTE) is rNDE multiplied by rNIE]. Results: In both cohorts, most individuals (∼68%) were never obese in adulthood, 16-30% became obese and ≤11% were always obese. In 1946-NSHD, rTE of incident obesity at 43 years (vs never) on poor PF was 2.32 (1.13, 3.51); at 53 years it was 1.53 (0.91, 2.15). rNIEs via inactivity were 1.02 (0.97, 1.07) and 1.02 (0.99, 1.04), respectively. Estimated rTE of persistent obesity from 36 years was 2.91 (1.14, 4.69), with rNIE of 1.03 (0.96, 1.10). In 1958-NCDS, patterns of association were similar, albeit weaker. Conclusions: Longer duration of obesity was associated with increased risk of poor PF. Inactivity played a small mediating role. Findings reinforce the importance of preventing and delaying obesity onset to protect against poor PF.

Publication metadata

Author(s): Pereira SMP, De Stavola BL, Rogers NT, Hardy R, Cooper R, Power C

Publication type: Article

Publication status: Published

Journal: International Journal of Epidemiology

Year: 2021

Volume: 49

Issue: 3

Pages: 845-856

Print publication date: 01/06/2020

Online publication date: 06/03/2020

Acceptance date: 17/01/2020

Date deposited: 12/01/2022

ISSN (print): 0300-5771

ISSN (electronic): 1464-3685

Publisher: Oxford University Press


DOI: 10.1093/IJE/DYAA014

PubMed id: 32142119


Altmetrics provided by Altmetric


Funder referenceFunder name
Department of Health Policy Research Programme
Public Health Research Consortium (PHRC)