Nitrates & nitrites (preservatives)
Nitrates and nitrites are chemicals found naturally in some foods, or added to others as a preservative. But there is concern that foods containing nitrite, particularly cured meats, may be linked to cancers. Learn more about these chemicals, where they're found, and how they may affect your health.
What are nitrates and nitrites?
Nitrates and nitrites are chemical compounds that occur naturally in the environment and are important plant nutrients. They have also been used to preserve food, especially meats, for hundreds of years.
Foods that contain nitrates and nitrites
Sources of nitrates and nitrites include:
- fresh vegetables, where they occur naturally – amounts are generally low, but can be higher depending on the type of vegetable and how it's grown. Hothouse vegetables and hydroponically grown leafy vegetables have higher nitrate levels. Celery, spinach, silverbeet, lettuce and potatoes contain the highest levels.
- drinking water – can be a significant source of nitrate and, sometimes, nitrite. For bottle-fed infants, it's the main external source
- meat – both nitrites and nitrates are used to improve the colour of processed meat products or as a preservative. It's used in products including bacon, ham, saveloys (but not sausage or sausage meat), luncheon, salami, corned silverside, and hamburgers
- cheese and cheese products – nitrates are added as a preservative.
Food code regulates use
The use of nitrate or nitrites as additives is regulated by Food Standards Australia New Zealand (FSANZ). They can only be added to specified foods, and can't exceed the maximum levels given in the Australia New Zealand Food Standards Code.
Acceptable daily intakes for nitrates and nitrites
The acceptable daily intake (ADI) tells you how much of a specific food additive you can safely eat each day, over the course of your life.
The average adult New Zealander eats about:
- 14% of the ADI of nitrite, and
- 18% of the ADI of nitrate.
Health concerns about nitrites and nitrates
Eating high levels of nitrite may pose a risk to your health, and eating high levels of nitrates can also be a risk, because your body converts 5% to 20% of nitrates you eat into nitrites. People who convert nitrates to nitrites at a rate of 20% are called high converters, and are more at risk of an adverse health effect.
However, your chances of eating unsafe amounts of nitrates and nitrites are very low – the average New Zealand adult eats less than 20% of the ADI over their lifetime.
About 10% of people with an average rate of nitrate to nitrite conversion, and half of all “high converters”, are estimated to sometimes exceed the ADI.
Cancer link not proven
Many studies have investigated if there is a link between nitrite and nitrate intake and – primarily stomach – cancers. This research is ongoing, but to date there is no convincing evidence showing that nitrate/nitrite consumption leads to cancer.
The World Health Organization has looked at the effects of nitrates and nitrites, and concluded they are not carcinogenic.
Nitrites effect on infants
In infants, nitrite may interact with haemoglobin in the red blood cells and cause methaemoglobinaemia, a condition that reduces the ability of blood to transport oxygen. This condition mostly affects infants under 3 months old, and is very rare in New Zealand.
Should you limit your intake?
Vegetables are New Zealanders' largest source of nitrates, and a major source of nitrites. However, the benefits of eating vegetables outweighs any risk, particularly because processes such as washing, boiling, and steaming will significantly reduce levels. Some countries – including those in Europe – have set limits for nitrate levels in specific vegetables. New Zealand has no set limits for vegetables, but spinach and lettuce tested were within European limits.
In 2015, the World Health Organization's International Agency for Research on Cancer (IARC) identified processed meat as carcinogenic to humans. However, it didn't look at what aspect of processed meats (for example, preparation or components) was the likely carcinogen.
Until we have more information on these issues, you may wish to limit your intake of processed meats.