The following article attributes a causal role in lowering blood pressure for nitrates in fruit and vegetables (I am positive it is more than just that), and the authors of the following article might support the supplementation of diets with nitrate salts alone.
Possibly that would be a mistake – nitrosamines and cancer being the obvious problem.
Could the vitamin C in fruits and green leafy vegetables (which would consume some of the oxygen in the ingested air, said oxygen being that which converts nitrites into the better nitrosating agents, N2O3 and N2O4) help us get the benefits of extra NO production from nitrates via nitrites (using entero-salivary circulation with an assist from facultative anaerobes living on the dorsal surface of our tongues) while reducing the generation of nitrosamines?
And is it not odd that people worry about nitrites in preserved meats, when nitrates in spinach and other vegetables (and fruits) are readily converted to nitrites in our mouths? Clearly spinach has the vitamin C to help protect us from the nitrite production, and if we took grams of vitamin C per day, as Pauling recommended, we would have even less worry about nitrites becoming nitrosamines in our stomachs and intestines.
Here is the article:
Hypertension. 2008 Mar;51(3):784-90. doi: 10.1161/HYPERTENSIONAHA.107.103523. Epub 2008 Feb 4.
Acute blood pressure lowering, vasoprotective, and antiplatelet properties of dietary nitrate via bioconversion to nitrite.
Webb AJ1, Patel N, Loukogeorgakis S, Okorie M, Aboud Z, Misra S, Rashid R, Miall P, Deanfield J, Benjamin N, MacAllister R, Hobbs AJ, Ahluwalia A.
Diets rich in fruits and vegetables reduce blood pressure (BP) and the risk of adverse cardiovascular events. However, the mechanisms of this effect have not been elucidated. Certain vegetables possess a high nitrate content, and we hypothesized that this might represent a source of vasoprotective nitric oxide via bioactivation. In healthy volunteers, approximately 3 hours after ingestion of a dietary nitrate load (beetroot juice 500 mL), BP was substantially reduced (Delta(max) -10.4/8 mm Hg); an effect that correlated with peak increases in plasma nitrite concentration. The dietary nitrate load also prevented endothelial dysfunction induced by an acute ischemic insult in the human forearm and significantly attenuated ex vivo platelet aggregation in response to collagen and ADP. Interruption of the enterosalivary conversion of nitrate to nitrite (facilitated by bacterial anaerobes situated on the surface of the tongue) prevented the rise in plasma nitrite, blocked the decrease in BP, and abolished the inhibitory effects on platelet aggregation, confirming that these vasoprotective effects were attributable to the activity of nitrite converted from the ingested nitrate. These findings suggest that dietary nitrate underlies the beneficial effects of a vegetable-rich diet and highlights the potential of a “natural” low cost approach for the treatment of cardiovascular disease.
Mother was right: eat your vegetables and do not spit! When oral nitrate helps with high blood pressure. [Hypertension. 2008]
PMID: 18250365 PMCID: PMC2839282 DOI: 10.1161/HYPERTENSIONAHA.107.103523
[PubMed – indexed for MEDLINE] Free PMC Article
And of course, this effect is not always observed, and was not observed in at least one study on people who are taking medication for high blood pressure (where ironically, it would be most needed). For example, Am. J. Clin Nutr. 2015, 102:368-375.