Nitrate with the chemical formula NO₃^- is one of the forms of nitrogen in the environment that plays an important role in the nitrogen cycle. Vegetables, water and meat are important sources of nitrate. Nitrate is made in the body through the arginine-NO pathway and enters the body through various sources. Oral nitrate is converted to nitrite (NO₂^-) by bacteria when it enters the mouth, and nitrite is converted to a carcinogen called nitrosamine after it enters the stomach. Many studies have confirmed the effect of nitrate on carcinogenesis in forty animal species. Nitrate can cause methemoglobinemia, cancers, thyroid diseases and tumors. On the other hand, the positive effect of nitrate on blood vessel health and the muscle-building process has been confirmed. The use of microbial agents and biofertilizers to reduce the residue of chemical fertilizers in agricultural products can be useful. In this article, nitrate sources, its role in the nitrogen cycle and its impact on human health are investigated. Also, the use of plant growth-promoting bacteria to reduce nitrate concentrations in greenhouse crops is described as a practical method.