- Print Friendly - Help

Nitrates and nitrites in our food

Nitrates and nitrites are chemical compounds that occur naturally in the environment and are important plant nutrients, but can also be added to some food products as a preservative. Nitrates and nitrites have been used to preserve food for hundreds of years but there is concern that they may be linked to cancers.

In some circumstances, drinking water can be a significant source of nitrate and, occasionally, nitrite. In the case of bottle-fed infants, drinking water may be the major external source of exposure to nitrate and nitrite.

The concentration of nitrite in fresh vegetables is generally low but vegetables may contain variable amounts of nitrate, depending on the method of cultivation, the rate and timing of fertiliser application, light intensity, daytime temperature and soil characteristics.

Vegetables grown in heated glasshouses have higher nitrate contents than those grown outdoors, and hydroponically grown leafy vegetables have higher nitrate levels than conventionally grown.

Both nitrites and nitrates can be added (for example as potassium or sodium nitrite [249, 250] or potassium or sodium nitrate [251, 252]) to meat products including bacon, ham, saveloys (but not sausage or sausage meat), luncheon, salami, corned silverside, and hamburger. Cheese and cheese products usually have only nitrates added.

Nitrates and nitrites help preserve food

• Nitrite may be added to meat products to prevent food spoilage or to maintain the colour of the meat.

• Nitrate is used in meat products as a source of nitrite, which is the agent that prevents spoilage. In cheese, nitrates are used as a preservative.

Effects of nitrates and nitrites on the body

We are exposed to nitrite and nitrate when we eat vegetables and processed meats. Celery, lettuce and potatoes have been found to contain relatively high concentrations of nitrate.

The human body is able to convert 5% to 20% of the nitrate in food into nitrite (known as endogenous nitrite). The small quantities of permitted added nitrates or nitrite are described as exogenous (originating externally) nitrates and nitrites.

In infants nitrite may interact with haemoglobin in the red blood cells resulting in a condition known as methaemoglobinaemia, causing blood to be less efficient in transporting oxygen. This condition, which occurs almost exclusively in infants under 3 months of age, has occurred extremely rarely in New Zealand. A significant number of epidemiological studies have been carried out on the association of nitrate intake with primarily stomach cancers. Although the data are inadequate to allow definitive conclusions to be drawn regarding all cancers, there is no convincing evidence of causal association with any cancer.

Acceptable amounts of nitrates and nitrites in the daily diet

A safe daily limit, known as the Acceptable Daily Intake (ADI), has been set for the amount of nitrite we eat. Because some nitrate from food is converted to nitrite in our body, there is also an ADI for the amount of nitrate we eat.

• The current acceptable amount of nitrite in a daily diet is up to 0.07 mg of nitrite per kg of body weight per day. For a person weighing 70 kg, this would be about 5 mg per day.

• The acceptable daily limit of nitrate is up to 3.7 mg per kg of body weight per day, or 260 mg per day for a 70 kg person.

Levels of nitrates and nitrites allowed in food

• Vegetables

As the exposure to nitrates and nitrites has largely been from natural sources which are difficult to separate from that which has been deliberately added, and also has not been found to be a significant health risk to date, there are no limits for the amount of nitrate allowed in vegetables consumed in New Zealand. In Europe the limits in winter and summer are 3000 and 2500 mg nitrate per kg fresh spinach. Preserved or frozen spinach may contain up to 2000 mg per kg spinach. Lettuces eaten in Europe may contain between 2000 and 4500 mg nitrate per kg of lettuce depending on whether they are grown in the winter or summer and under cover or in the open air. New Zealand lettuce and spinach samples tested were within the limits set for Europe. The amounts of nitrate in New Zealand spinach ranged from 100 to 1560 mg per kg of cooked spinach and the amounts in New Zealand lettuces were between 83 and 3420 mg per kg of fresh lettuce.

• Meat and cheese

Bacon, ham, saveloys, luncheon sausage, salami, pizza, corned silverside, and hamburger eaten in New Zealand may contain up to 125 mg of total nitrite and nitrate per kg of the food. Cheese and cheese products may contain up to 50 mg of nitrate per kg of food.

Sausage, sausage meat and mince are not allowed to contain nitrate or nitrite.

The amount of nitrates and nitrites we eat

An average adult New Zealander eats about 0.01 mg per kg of body weight per day or 14% of the ADI of nitrite and 0.7 mg per kg of body weight per day, or 18% of the ADI of nitrate.

When we allow for some of the nitrate from food being converted to nitrite in the body, approximately 10% of people with an average rate of conversion and half of all people with a high rate of conversion are estimated to exceed the ADI.

Who is most at risk from consuming nitrates and nitrites?

Those people who eat a lot of lettuce and those who have a high rate of conversion of nitrate to nitrite are potentially most at risk to health damage from nitrate but to date there has been no evidence that this is a problem. At this time we do not know how many of the population are high converters of nitrate to nitrite but we do know that conditions related to overexposure remain rare.

Health benefits of vegetables outweigh nitrate/nitrite low risks

Vegetables are the major source of total exposure to nitrates and nitrites. Since vegetables are good for health it is important to maintain these in our diet. The contribution of nitrite used to keep processed meats and cheese appealing and safe is small and there is currently no evidence that it poses a health risk.

Last updated March 2009