Occurrence in food
Nitrate (nitrate ion NO 3-) is a naturally occurring compound involved in the nitrogen cycle. Nitrate occurs naturally in plants. It is also made up of nitrogen compounds in food in the human body and is custom
Nitrate is mainly obtained from natural sources such as vegetables. Leafy vegetables , for example, are naturally nitrate-rich.
Nitrate content in vegetables varies depending on the species. There is also variation between different parts of the vegetable. Nitrate moves towards the leaves with water and nutrients in the plant. This is why the highest levels are usually found in green leafy vegetables, while levels in seeds and stems are lower. In potatoes, the highest nitrate content is in the skin, but in carrots and beetroot in the middle. The nitrate content of lettuce is highest in the outermost leaves. In addition, plant age affects the nitrate content: the youngest leaves contain less nitrate than the older leaves.
Nitrate levels are affected by both agricultural practices and environmental factors. Fertiliser, soil moisture, the amount of light, temperature and variety are factors that affect plant nitrate levels. Abundant light reduces nitrate levels. A dry growing season, in turn, increases nitrate levels in vegetables. Planting density, substrate and irrigation are also important. The cold chain and market speed prevent the products from drying out and the nitrate content from rising.
Adverse health effects
High nitrate intake causes methemoglobinemia. Methaemoglobin is a form of haemoglobin that has poor ability to carry oxygen. Higher-than-normal levels of methaemoglobin may manifest as cyanosis, a bluish discolouration of the skin. Methemoglobinemia can be dangerous, especially in young children. Nitrate is a water-soluble compound and most of the intake from food is removed from the body by the kidneys.
Nitrite formed from nitrate in metabolism has been suspected to increase the risk of diabetes, coronary heart disease and cancer, but research findings are somewhat contradictory and no direct causal link has been established to date.
The Joint Expert Committee on Food Additives (JECFA) of the FAO and WHO has determined an Acceptable Daily Intake (ADI) of nitrate of 3.7 mg/kg bw/d. The European Food Safety Authority EFSA has also used this ADI in its assessments.
Maximum levels in food
EU legislation ((EC) No 1881/2006 as amended) sets maximum levels for nitrate in spinach, fresh lettuce, iceberg lettuce, rocket, processed cereal-based foods and baby foods for infants and young children.