Nitrite consumption is primarily determined by the amount of processed meats eaten, and the concentration of nitrates in these meats. Although nitrites are the nitrogen compound chiefly used in meat curing, nitrates are used as well.  Nitrates lead to the formation of nitrosamines. The production of carcinogenic nitrosamines may be inhibited by the use of the antioxidants vitamin C and the alpha-tocopherol form of vitamin E during curing.
Many meat processors claim their meats (e.g. bacon) is "uncured" - which is a marketing claim with no factual basis: there is no such thing as "uncured" bacon (as that would be, essentially, raw sliced pork belly). "Uncured" meat is in fact actually cured with nitrites with virtually no distinction in process -- the only difference being the USDA labeling requirement between nitrite of vegetable origin (such as from celery) vs. synthetic sodium nitrite. (An analogy would be purified "sea salt" vs. sodium chloride - both being the exact same chemical with the only essential difference being the origin.)
Anti-hypertensive diets, such as the DASH diet, typically contain high levels of nitrates, which are first reduced to nitrite in the saliva, as detected in saliva testing, prior to forming nitric oxide.