Nitrates are natural compounds in the nitrogen cycle between air, water, and living organisms. NO3- molecules are relatively safe for humans, are easily formed in our body, are components of saliva, are converted in the liver, and are excreted in the urine. The main sources of nitrates for humans are naturally enriched plants such as beets, spinach, arugula, celery, and other green leafy vegetables. Once in the human body, nitrates are converted into nitrites, NO2-, under the influence of oral bacteria, which then become a source for the formation of nitric oxide.
NO is an important signaling molecule in the body. It relaxes the smooth muscles of the vascular wall, which results in lower blood pressure and improved blood supply. Studies have shown a positive effect of nitric oxide on the duration and strength of physical labor, kidney function, and aging processes.
In the presence of amino acids and at high temperatures, nitrites can form nitrosamines, substances that WHO has classified as carcinogens. Such conditions are created in meat when it is marinated with subsequent smoking, grilling, and in the production of sausages, when nitrates are added as preservatives (nitrates prevent the growth of pathogenic bacteria, including the pathogen botulism) and to improve the appearance (red-pink color) and taste (salinity). Some studies have shown that there is a link between high consumption of smoked meat and an increased risk of colon and rectal cancer.
However, a number of other analytical studies have failed to confirm the development of cancer as a result of nitrosamines. U.S. government regulations force producers to use limited amounts of nitrates and nitrites to preserve meat and to add ascorbic acid, which reduces the formation of nitrosamines.
The presence of large amounts of nitrates in drinking water due to excessive soil fertilization and contamination of water with animal feces can cause negative effects on the blood. Nitrites, interacting with hemoglobin, convert it into the form of methemoglobin, which is unable to attach and transport oxygen. Studies have shown that children under 6 months of age are the most sensitive to these changes in hemoglobin, which can cause cyanosis of the skin, vomiting, and known fatalities. In adults, nitrate poisoning will be accompanied by headaches, fatigue, and other symptoms of hypoxia.
WHO reports, relevant European and American institutions indicate the permissible daily intake of nitrates in the range of 0-3.7 mg per kilogram of body weight per day, separately highlighting only the maximum permissible amount of these compounds in water – 10 mg/l for nitrates and 1 mg/l for nitrites. The US Agency for Toxic Substances and Disease Registry, as well as an Australian institution with similar competencies, in their report highlight the content of nitrates (up to 500 mg/kg) and nitrites (up to 200 mg/kg) permissible for their use in the production of meat products and sausages.
The order of the Ministry of Health dated 13.05.2013 contains a large list of vegetables and fruits with the maximum permissible level of nitrates, the Laboratory Center of the Sanitary and Epidemiological Service of Ukraine cites 5 mg as the maximum permissible amount of these compounds per kilogram of human weight per day.
If we recalculate according to the recommended values of the Ministry of Health, then for a person weighing 60 kg, it will be safe to eat 300 mg of nitrates per day. This is, for example, 5 kg of watermelon, or 10 kilograms of spinach, or one and a half kilograms of smoked meat or sausages that are produced or grown in accordance with state safety requirements.
Every year, Ukrainians are urged to consume watermelons and melons with caution due to the presence of nitrates. Journalists and experts warn against eating early vegetables and emphasize dangerous levels of nitrates in cabbage and cucumbers. Government officials and the public are trying to control the nitrate content of crop products on their own. Instead, in Western countries, when writing about nitrates, they emphasize the maximum permissible dose for humans, the testing of drinking water and soil as the main source of excess nitrates, and the refusal to consume meat products containing potentially dangerous nitrosamines, without ignoring the powerful positive effects of nitrates on the cardiovascular system.