## 4 The Effect of Reduced N Fertilization on Human Health and Food Quality  
Excessive and often unbalanced N fertilization in agriculture poses significant risks to both human health and environmental sustainability. The lack of guidance on optimal N application often leads to overuse by farmers. The presence of high levels of NO3\({}^{-}\) in crops, particularly leafy vegetables such as spinach, lettuce, and beets, poses potential health risks [105]. When consumed, these NO3\({}^{-}\) can convert into NO2\({}^{-}\), which can form NOCs--carcinogenic compounds linked to an increased risk of cancers, especially in the stomach and esophagus [2; 3; 105; 106]. Managing the levels of NO3\({}^{-}\) and NO2\({}^{-}\) in food is crucial, as prolonged exposure can elevate health threats, particularly when combined with processed meat consumption [106]. Reducing N fertilizer usage has been shown to enhance the quality and weight of food products. [PERSON] et al. [107] conducted studies describing the impact of N fertilization and postharvest treatments on fresh-cut celery, demonstrating that the highest loss of vegetable mass occurred with the highest level of N fertilization; however, as a result of the applied doses of fertilization, the level of vitamin C was improved with N fertilizers. [PERSON] [108] also observed a decrease in the amount of vitamin C due to N fertilization among potatoes, tomatoes, and citrus fruits. Excessive N fertilization in agriculture often leads to a dilution effect, where the increased vegetative growth results in lower concentrations of vitamin C in vegetables [104]; it can therefore be suggested that the increased biomass of the plant does not correspond to a proportional increase in the minerals and vitamins that are essential for human health. Healthy soils that are not overloaded with chemicals promote more effective nutrient absorption by plants. As a result, it can be assumed that crops grown in such environments may not only be more nutritious but may also align with consumer preferences for food perceived as more natural and of higher quality. The environmental consequences of excessive N fertilization are profound, particularly concerning groundwater quality and overall ecosystem health. When NO3\({}^{-}\) is not absorbed by plants, it can leach into groundwater and surface water, leading to significant contamination issues [3]. After the intake of NO3\({}^{-}\), which is present in many plant-based foods and drinking water, it is absorbed in the gastrointestinal tract and undergoes conversion to NO2\({}^{-}\) and NOCs through a series of biochemical reactions, particularly in the mouth and stomach [109; 110]. In the presence of anaerobic bacteria, NO3\({}^{-}\) is reduced to NO2\({}^{-}\). This reaction is catalyzed by bacterial nitrate reductase, which converts NO3\({}^{-}\) to NO2\({}^{-}\)[110]. As a result of this reduction, NO2\({}^{-}\) is absorbed and transported to the stomach, where a highly acidic environment prevails. Under the influence of gastric acid, NO2\({}^{-}\) decomposes into, among other products, nitric oxide (NO), but it can also react with the amines present in food, leading to the formation of NOCs, which are carcinogenic. This process is particularly intense when consuming processed meats, where NO3- and NO2- are added as preservatives, thus increasing the risk of NOC formation in the body [106; 109]. The consumption of nitrate-laden water can lead to methemoglobin, thyroid dysfunction, gastrointestinal cancers, breast cancer, bladder, and neurodevelopmental disorders including neural tube defects [3; 109]. Methemoglobin is a condition where NO3- is converted to NO2- in the body, leading to the formation of methemoglobin. This compound reduces the blood's ability to carry oxygen, which can be particularly dangerous for infants under six months of age, pregnant women, and individuals with certain genetic conditions or health issues [109; 111].