GGT1 and breast cancer: In contrast, Yuvaraj et al. examined the effect of CoQ10 combined with riboflavin and niacin on serum GGT and serum AST in Tamoxifen-treated postmenopausal women with breast cancer[37] and found that the activity of both serum GGT and serum AST decreased in response to exogenous supplementation of CoQ10, niacin and riboflavin.