Endothelial function and cardiovascular risk: The preservation of the structural and functional integrity of the endothelium plays a critical role in the prevention of atherosclerotic damage and cardiovascular risk. Endothelial dysfunction has been identified as a surrogate physiological biomarker for cardiovascular risk prediction as well as a target of nutritional and pharmacological interventions (1). This prominent role is mechanistically explained by the selective activity of endothelial cells in regulating cellular and molecular trafficking between circulating fluids and interstitial space and several physiological functions via the secretion of molecules with paracrine and endocrine signalling properties. One of the most important secretory endothelial products is nitric oxide (NO), a gasotransmitter with paracrine and endocrine actions involved in the regulation of vascular resistance, immunity, coagulation, memory formation and mitochondrial efficiency (1). Nitric Oxide Pathway: NO can be synthesised in humans through an enzymatic and non-enzymatic pathway. The endothelial isoform of Nitric Oxide Synthase (eNOS) uses arginine and molecular oxygen as precursors to tonically release NO. The efficiency of the enzymatic pathway is dependent on the availability of several cofactors including flavin adenine dinucleotide (FAD), flavin mononucleotide (FMN), heme, tetrahydrobiopterin (BH4) and calmodulin. The non-enzymatic pathway is based on the progressive reduction of inorganic nitrate into nitrite (NO2-) and NO in a complex system involving the recovery of circulating plasma nitrate through the salivary glands (entero-salivary circulation), reductase activity of saprophytic oral bacteria and reductase-specific activity of enzymes in conditions of low pH and oxygen tension (2, 3). Nutrition and the NO pathway: Nutritional strategies to increase NO production can target the different elements of the NO pathway by increasing the bioavailability of the NO precursor (arginine) and co-factors (antioxidants, folic acid) and/or raise the non-enzymatic generation of NO (inorganic nitrate). L-Arginine appears to dilute the intracellular levels of asymmetric dimethylarginine (ADMA), an endogenous inhibitor of eNOS. Levels of ADMA are determined by the balance between synthesis and degradation regulated by two enzymes, i.e., protein arginine methyltransferases (PRMT) and dimethylarginine dimethylaminohydrolases (DDAH), respectively. The effects of inorganic nitrate derive from increased non-enzymatic and enzymatic generation of NO in environments with higher acidity and lower oxygen tension and specific host enzymes with NO2- reductase activity (i.e., xanthine oxido-reductase (XOR), deoxy-Hb) (2,3). Nutrigenomics of the NO pathway: The close mechanistic links between nutritional factors, enzymatic synthesis and degradation of NO represent an ideal feature for a multi-candidate gene-nutrient approach based on the following characteristics: 1) genes involved in NO metabolism are responsive to nutritional interventions; 2) genes are characterised by important functional variations; 3) genes can influence the synthesis and function of NO and have downstream, multi-systemic effects and 4) the prevalence of functional gene polymorphisms in the general population is meaningful and 5) the function of the genes can be directly assessed by measuring gene expression or direct (systemic NO production) and indirect biomarkers (nitrate, nitrite, cGMP, ADMA, flow mediated dilation) of NO production (4). The nutrigenomic approach to the NO pathway is gaining momentum and recent data from epidemiological and clinical studies have investigated the association of several single nucleotide polymorphisms (SnPs) in the genes involved in the regulation of the NO pathway including eNOS, arginase, DDAH, PMRT and XOR with health outcomes (4,5,6). For example, eNOS (G894T (Glu298Asp, rs1799983) in exon 7 and T786C (rs2070744) in the promoter region) and XOR polymorphisms (- 337GA, 565+64CT) have been associated with raised blood pressure (5,6). In addition, eNOS Glu298Asp genotype appeared to differentially affect vasodilation and ex vivo lipoprotein oxidation after consumption of fruit and vegetables in humans (7).Future Directions: The effects of the individual allelic variants for each SnPs in the various genes involved in the regulation of the NO pathway are far from being elucidated. In addition, there is currently limited evidence on the effects of nutritional factors acting on the two synthetic mechanisms of NO production (enzymatic and non-enzymatic) and their potential cross-interaction. The understanding of the differential responses of candidate genes to specific nutrients targeting the NO pathway may form the basis for a risk-stratified approach to nutritional treatments of chronic metabolic and cardiovascular disorders.