Background: The interpretation of research results is affected by how results are presented. We show the importance of presenting the association between body mass index (BMI) and healthcare costs from both the individual perspective and the population perspective.
Material and method: Using measurements of height and weight from the Nord-Trøndelag Health Study (HUNT Study) linked to register data on specialist healthcare costs and demographics, we estimated the association between BMI and specialist healthcare costs by means of regression analyses.
Results: From an individual perspective, the association between BMI and specialist healthcare costs was strongest in people in obesity classes 2 and 3 (BMI ≥ 35 kg/m2). In contrast, from a population perspective, the association was strongest in the case of overweight (BMI ≥ 25 kg/m2) or obesity class 1 (BMI ≥ 30 kg/m2), as there are more people in this BMI range.
Interpretation: The study emphasises the importance of including the population perspective in research studies and policy decision-making processes. People with severe obesity have a high individual risk, but their use of health services has less significance for the overall costs of health care since they are fewer people in this group.