Effect of the type of population on estimates of mean body mass index and prevalence of overweight and obesity: A systematic review of studies of Portuguese adults

Abstract

Background: Prevalence estimates for overweight/obesity vary widely between studies, reflecting true differences across settings and biased sampling.

Aim: To compare mean body mass index (BMI) and prevalences of overweight/obesity in samples of different types of population, in Portugal.

Methods: A systematic review was conducted to identify studies that assessed the distribution of BMI and overweight/obesity in different populations (general population, blood donors, university students, occupational groups, healthcare users and volunteers). Linear regression was used to quantify age-, sex- and survey year-adjusted differences in these outcomes.

Results: When weight/height were measured, BMI was higher among blood donors (+1.4 kg/m²) and lower in occupational groups ( − 0.9 kg/m²), compared to the general population. Overweight prevalence was lower among university students ( − 5.2%). Obesity prevalence was higher among occupational groups (+4.5%) and healthcare users (+8.9%); and lower in volunteers ( − 6.4%). With self-reported data, BMI was lower among university students ( − 0.9 kg/m²), occupational groups ( − 1.2 kg/m²) and volunteers ( − 0.7 kg/m²). Healthcare users had higher overweight (+6.7%) and lower obesity prevalences ( − 4.3%) and occupational groups lower obesity prevalence ( − 5.7%).

Conclusion: Estimates varied largely across population types. Commonly used solutions for an easier assembling of study samples are likely to yield biased estimates of the distributions in the general population.

Keywords::

• Data collection
• health surveys
• epidemiology

Acknowledgements

The authors gratefully acknowledge the collaboration of Catarina Vales and Vânia Rocha who screened the reference lists and extracted data. This study was funded by a grant from Fundação para a Ciência e a Tecnologia (PIC/IC/83006/2007).

Declaration of interest: The authors report no conflicts of interest. The authors alone are responsible for the content and writing of the paper.