Safety and efficacy of dietary freshwater clam (Corbicula fluminea) extract in clinical research

Background: The freshwater clam (Corbicula spp.) is a popular edible bivalve mollusk that is commonly eaten in East Asia. Freshwater clam extract (FCE) is known to have various effects. For example, it has anti-inflammatory effects and improves cholesterol metabolism. Often used as a folk remedy, FCE might be effective against liver disease and at ameliorating liver damage. These results indicate that FCE has preventative or ameliorating effects against steatosis and mild chronic liver damage. Additionally, FCE has a documented neuroprotective effect, potentially improving sleep quality. However, no clinical research into these topic areas have been carried out. Objective: No clinical research has been carried out concerning the action of FCE on liver function. In this study, we conducted a clinical trial involving healthy volunteers with relatively high liver test values to determine the influence of FCE on hepatic function. Moreover, no previous studies have described the effects of FCE on sleep. Thus, we also assessed sleep quality after FCE intake using the Oguri-Shirakawa-Azumi (OSA) sleep inventory middle-aged and aged (MA) version and a Likert scale in a randomized controlled clinical trial. Methods: We performed a prospective randomized controlled trial to assess safety and the effects of freshwater clam extract. Thirty four volunteers were analyzed. The subjects ingested 2 placebo softgels, 2 FCE-containing softgels, or 10 FCE-containing softgels. We tried to clarify 2 issues, safety in the liver and quality of sleep. An assessment of the safety of long-term and excessive FCE intake, especially its actions on hepatic function, was performed by administering 10 FCE-containing softgels (5 times the normal dose) to the subjects in the high FCE dose group for 18 weeks. A sleep evaluation comparing the placebo and normal FCE dose groups was also conducted. We conducted a double-blind parallel clinical trial to evaluate the effects of FCE on sleep quality over 12 weeks. The subjects were assigned to 3 groups (the placebo group, the normal FCE dose group, and the high FCE dose group). Results: Significant reductions in the levels of aspartate aminotransferase (AST), alanine aminotransferase (ALT), and γ-glutamyl transpeptidase (γ-GTP) were observed at 12 and 18 weeks after the consumption of a high dose of FCE capsules. The subjects’ ferritin levels were significantly reduced after 18 weeks’ high-dose FCE intake. Moreover, the consumption of two FCE softgels (normal dose) for 12 weeks resulted in significant better quality in terms of both sleep onset and maintenance compared with that seen after the placebo treatment. FCE intake also resulted in a longer sleep duration than the placebo treatment. The same dose of FCE tended to reduce subjective fatigue. These results suggest that FCE is a safe supplemental food and increases sleep quality.Conclusions: These results suggest that FCE is a safe supplemental food and increases sleep quality.Keywords:  freshwater clam, hepatotoxicity, randomized study, sleep