Aim of the study The aim of this paper was to conduct a systematic review of cost-of-illness studies for overweight and adiposity in Germany. Methods We conducted a PubMed search to identify relevant studies. To increase comparability, all cost data were inflated to 2014 prices. For bottom-up studies, we additionally calculated relative cost-differences between normal weight and overweight, as well as adiposity. These relative differences were pooled using meta-analytical techniques and extrapolated to the German population. Results We identified 15 bottom-up studies, 6 top-down studies and 2 Markov simulations. On average, top-down studies reported direct costs of 7.9 billion Euros and indirect costs of 3.6 billion Euros. Due to between-study heterogeneity, we were not able to pool absolute costs reported in bottom-up studies. The pooled relative cost-differences for studies conducted with adult persons were +22% for the difference between normal weight and overweight and +53% for the difference between normal weight and adiposity. The corresponding effect sizes were 0.07 (- 0.05; 0.19) and 0.15 (0.02; 0.28), respectively. In studies conducted with children and adolescents, relative cost-differences were considerably smaller with corresponding effect sizes being close to zero. Extrapolation of relative pooled cost-differences from bottom-up studies to the German total population yielded direct and indirect excess costs of 22.2 billion Euros for overweight and 23.0 billion Euros for adiposity. Conclusion We found substantial heterogeneity of cost findings between studies for top-down and bottom-up studies as well, which points to substantial uncertainty and strongly hampers clear statements about the costs of overweight and adiposity. Our findings imply that costs are underestimated by top-down studies, whereas overestimated by our extrapolation. The true costs presumably lie between the findings of both approaches.
