Background: In an intervention study where 221 healthy elderly persons received selenium and coenzyme Q10 as a dietary supplement, and 222 received placebo for 4 years we observed improved cardiac function and reduced cardiovascular mortality. As fibrosis is central in the aging process, we investigated the effect of the intervention on biomarkers of fibrogenic activity in a subanalysis of this intervention study. Material and Methods: In the present subanalysis 122 actively treated individuals and 101 controls, the effect of the treatment on eight biomarkers of fibrogenic activity were assessed. These biomarkers were: Cathepsin S, Endostatin, Galectin 3, Growth Differentiation Factor-15 (GDF-15), Matrix Metalloproteinases 1 and 9, Tissue Inhibitor of Metalloproteinases 1 (TIMP 1) and Suppression of Tumorigenicity 2 (ST-2). Blood concentrations of these biomarkers after 6 and 42 months were analyzed by the use of T-tests, repeated measures of variance, and factor analyses. Results: Compared with placebo, in those receiving supplementation with selenium and coenzyme Q10, all biomarkers except ST2 showed significant decreased concentrations in blood. The changes in concentrations, that is, effects sizes as given by partial eta(2) caused by the intervention were considered small to medium. Conclusion: The significantly decreased biomarker concentrations in those on active treatment with selenium and coenzyme Q10 compared with those on placebo after 36 months of intervention presumably reflect less fibrogenic activity as a result of the intervention. These observations might indicate that reduced fibrosis precedes the reported improvement in cardiac function, thereby explaining some of the positive clinical effects caused by the intervention. (c) 2017 BioFactors, 44(2):137-147, 2018