Finally, the smoking status, an important determinant of ADMA levels (as well as other variables, such as: hyperhomocysteinemia, hypertension, coronary artery disease, heart failure, and administration of the following drugs: antioxidants, estrogen, vitamin A, angiotensin converting enzyme inhibitors, angiotensin AT1 receptor antagonists, and beta-adrenoreceptor blocking drugs), could not be considered in this meta-analysis due to lack of data. This evidence concerns the gene ACE and heart failure.