Nitrates are part of the nitrogen cycle in the nature. They are found in air, soil, water and food, and can be produced inside living organisms. Plants need nitrogen-containing substances for growth, such as nitrates and ammonium salts, and utilise the absorbed nitrogen to synthesise amino acids. Farmers apply appropriate amounts of nitrogen-based fertilisers to crops for healthy growth.
Why are nitrates found in processed foods?
Nitrates are added to food mainly for preservation and colour retention. Nitrates and nitrites are applied to common food products such as cheese, cheese products as well as processed meat (e.g. ham and sausages). Upon ingestion, the nitrates and nitrites may be converted into N-nitroso compounds (NOC) during the digestion process in our stomach. Since N-nitroso compounds can induce cancer in experimental animals, the use of nitrates and nitrites in food has raised safety concerns.
Do vegetables contain high levels of nitrates?
Natural foods like fruit and vegetables (e.g. root vegetables), edible meat and drinking water contain trace amounts of nitrates, among which the level of nitrates in vegetables is the highest. Human intake of nitrates occurs mainly through ingestion of vegetables and secondarily through contaminated drinking water and processed foods. The amount of nitrates in vegetables varies across the species, their edible parts, growing seasons, light intensity, temperature, fertilisers, locations of storage and processing. For instance, vegetables like broccoli and eggplant contain less nitrates whereas spinach and amaranth have higher levels of nitrates.
Is there a limit for daily intake of nitrate?
In 2002, the Joint FAO/WHO Expert Committee on Food Additives (JECFA) has set the acceptable daily intake (ADI) of nitrates as 3.7 mg per kilogram of body weight per day (mg/kg bw/day), which is equivalent to 222 mg nitrate per day for an adult weighing 60 kg.
Despite the presence of nitrates, vegetables are essential to human health as a source of dietary fibre, vitamins and minerals. They are an indispensable part of human diet. The European Food Safety Authority (EFSA) has evaluated the risks of exposure to nitrates in vegetables and concluded that “The estimated exposures to nitrate from vegetables are unlikely to result in appreciable health risks; therefore, the recognised beneficial effects of consumption of vegetables prevail”. After all, the public should maintain a balanced diet and avoid eating only one type of food.
Source:
ADI:
https://apps.who.int/food-additives-contaminants-jecfa-database/chemical.aspx?chemID=709
HKCFS:
https://www.cfs.gov.hk/english/multimedia/multimedia_pub/multimedia_pub_fsf_25_01.html
EFSA:
https://www.efsa.europa.eu/en/press/news/080605
011/DIR/DSA/2020
