Objective To examine whether occupational physical activity changes predict future body mass index (BMI) changes.
Methods This longitudinal cohort study included adult participants attending ≥3 consecutive Tromsø Study surveys (examinations 1, 2 and 3) from 1974 to 2016 (N=11 308). If a participant attended >3 surveys, the three most recent surveys were included. Occupational physical activity change (assessed by the Saltin-Grimby Physical Activity Level Scale) was computed from the first to the second examination, categorised into persistently inactive (n=3692), persistently active (n=5560), active to inactive (n=741) and inactive to active (n=1315). BMI change was calculated from the second to the third examination (height being fixed at the second examination) and regressed on preceding occupational physical activity changes using analysis of covariance adjusted for sex, birth year, smoking, education and BMI at examination 2.
Results Overall, BMI increased by 0.84 kg/m2 (95% CI 0.82 to 0.89). Following adjustments as described previously, we observed no differences in BMI increase between the occupational physical activity change groups (Persistently Inactive: 0.81 kg/m2, 95% CI 0.75 to 0.87; Persistently Active: 0.87 kg/m2, 95% CI 0.82 to 0.92; Active to Inactive: 0.81 kg/m2, 95% CI 0.67 to 0.94; Inactive to Active: 0.91 kg/m2, 95% CI 0.81 to 1.01; p=0.25).
Conclusion We observed no prospective association between occupational physical activity changes and subsequent BMI changes. Our findings do not support the hypothesis that occupational physical activity declines contributed to population BMI gains over the past decades. Public health initiatives aimed at weight gain prevention may have greater success if focusing on other aspects than occupational physical activity.
- public health
- longitudinal studies
- preventive medicine
- physical work
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Twitter @edvardhsagelv, @Ulf_Ekelund, @lailahopstock, @mariusfimland, @MorsethBente
Contributors EHS, BM, UE and LAH designed the study; EHS carried out statistical analyses; OL and TW provided statistical expertise; EHS drafted the manuscript; all authors interpreted the study results and contributed with manuscript revisions and approved the final version of the manuscript.
Funding The work of EHS is funded by Population Studies in the High North (Befolkningsundersøkelser i Nord: BiN), an internally funded project by UiT The Arctic University of Norway (no grant/award number). The remaining authors are funded by their respective positions/tenures.
Competing interests None declared.
Patient consent for publication Not required.
Ethics approval All participants in Tromsø 4–7 provided written informed consent, and the present study was approved by the Regional Ethics Committee for Medical Research (ref. 2016/758410).
Provenance and peer review Not commissioned; externally peer reviewed.
Data availability statement Data may be obtained from a third party and are not publicly available. The data that support the findings of this study are available from the Tromsø Study, but restrictions apply to the availability of these data, which were used under licence for the current study, and so are not publicly available. The data can be made available from the Tromsø Study upon application to the Data and Publication Committee for the Tromsø Study (see www.tromsostudy.com).
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