Patients with Long COVID experience a significant decrease in their quality of life and the lack of effective treatment represents an unmet need in medical care and patient health. One proposed strategy for treating Long COVID is to increase the ability of the body to restore immune balance by controlling inflammation with anti-inflammatory substances. For this reason, the aim of this double-blind study was to evaluate the supplementation of patients with EchA Marine, a dietary supplement based on sea urchin eggs rich in Echinochrome A. This compound has demonstrated anti-inflammatory and antioxidant properties by activating the metabolism of glutathione and improving mitochondrial mass and performance. The EuroQol 5-Dimension (EQ-5D) is a standardized questionnaire assessing five dimensions of health: mobility, self-care, usual activities, pain/discomfort, and anxiety/depression used as an instrument to measure health-related quality of life in clinical and economic studies. In this multicenter, double-blind, intervention study, we have demonstrated that the dietary supplement EchA Marine can significantly enhance the quality of life of these patients, particularly in pain and discomfort; notably improving their quality of life and ability in daily activities. EchA Marine is an effective treatment option for Long COVID patients and with further research its efficacy could be further strengthened. Clinical trial registration number:NCT05531019. First posted September 7th, 2022.