Nitrates and Nitrites in Food and Vegetables

Capture33Why not have a salad for breakfast, especially when it contains Mom and Dad’s home-grown lettuce? Because they either use no fertilizer or in the odd year composted manure, it’s lower in nitrates ( I measured about 250 ppm, relatively low for lettuce). Fresh manure can contaminate it with both nitrates and bacteria, while most synthetic fertilizer will also increase the concentration of the ion and more significantly.

If the recommended amount of inorganic fertilizer (200 kg·N·ha−1) is used as a standard of comparison, lettuce augmented with organic fertilizers (200 kg·N·ha−1) have significantly longer and wider leaves, higher shoot, and lower concentrations of nitrate.

The amount of nitrate from synthetic Other vegetables and fruits known to be high in nitrates include spinach and strawberries. Here’s more on why nitrates can be harmful and what foods contain them.

  1. Why worry about nitrates (NO3) and nitrites NO2?

Here’s the latest health effect summary(italicized) from the Environmental Protection Agency

A)                 Excessive levels of nitrate in drinking water have caused serious illness and sometimes death. The serious illness in infants is due to the conversion of nitrate to nitrite by the body, which can interfere with the oxygen-carrying capacity of the child’s blood. This can be an acute condition in which health deteriorates rapidly over a period of days. Symptoms include shortness of breath and blueness of the skin.

One author (Martijn Katan ) who is a nutritionist argued here ( that what’s being described above (methemoglobinemia ) is actually caused by bacterial contamination and subsequent production of nitrogen monoxide. But that was one conclusion from an experiment in the 1950s. Meanwhile, reputable medical sources (such as point out that nitrites and nitrates can cause methemoglobinemia , and it can also be brought about by a host of other compounds according to several sources that show up in Google Scholar under “causes of  methemoglobinemia”.

B)                 Drinking water levels which are considered “safe” for short-term exposures: For a 10-kg (22 lb.) child consuming 1 liter of water per day, a ten-day exposure to 10 mg/L total nitrate/nitrite.

C)                  Chronic: Effects of chronic exposure to high levels of nitrate/nitrite include diuresis, increased starchy deposits and hemorrhaging of the spleen.

D)        Cancer: There is inadequate evidence to state whether or not nitrates or nitrites have the potential to cause cancer from lifetime exposures in drinking water.

So it is still a possibility given that their presence and impact can combine with that of known carcinogens in the environment. Nitrates and nitrites are not themselves carcinogenic but they can form cancer-causing nitrosamines in the gut.

  1. What foods are sources of nitrates and nitrites?

Bacon particularly along with cold cuts and hot dogs have nitrites added to them either in the form of sodium nitrite or celery salt. But erythorbic and ascorbic acids are also added to prevent nitrosamine formation. Meanwhile spinach, especially, and lettuce can also have concentrations of nitrate that can be as high as those of bacon. But it depends on how they’re grown! If they are grown with composted manure, legume-enriched soil or with no fertilizer at all, these vegetables will have safe levels of nitrates. What elevates their concentration is liquid synthetic nitrates, some other nitrogen fertilizers and fresh manure, especially that of chickens. It should also be noted that outer leaves of lettuce have more nitrates than the inner leaves, since they have more time to concentrate them.

3. What happens to nitrites in processed meats?

Nitrites from cold cuts that have been rendered red by the addition of nitrites (hot dogs that  are made from byproducts are pale in color without nitrite) can form nitrosamines . Certain antioxidants added along with nitrites are supposed to prevent this. It works in most cases except in fried bacon, cured meats and salami, which contain between 2 and 11 ppb of nitrosamines(specifically, N-nitrosodimethylamine). Interestingly the nitrosamines in raw fish are volatile and do not show up in the analyses of cooked fish.

4. Can Excess Nitrates from Fruits and vegetables End Up As Nitrosamines?

Salivary glands and microbes in saliva are capable of converting some nitrates to nitrites, which subsequently, under the stomach’s acidic conditions can end up as nitrosamines. Some nitrites end up as nitrogen monoxide, which can have beneficial effects.

Another factor to consider is the serving size of cured meats and salami relative to that of a salad. Four slices of a cold cut has twice the mass of a serving of lettuce. So even if the compared foods contain an equal concentration of nitrites/nitrates, eating treated meat would expose you to twice the amount. Add lettuce to the cold cuts and that amount rises further.


J Sci Food Agric. 2014 Mar 15; 94(4):773-8.


Nitrite In The Hot Dogs Of My Youth

Rewritten: November 2014 I had filtered the tone and content of the original piece written in 2011 for fear that it would be shot down on a conservative website that once hosted my blogs. But I’ve decided to reveal the rest of the story.

nitritesI hope that Health and Welfare Canada guidelines for certain additives are a bit more stringent than they have to be to help compensate for possible loose play on the part of industries. When I was a student and shortly after I graduated, I analyzed fat content, dextrose and nitrite levels in hot dogs and other meat products for a well-known company. I’m not naming the company because for all I know they may have mended their ways. Also, I never gathered evidence that the whole industry was or is guilty of the things that I witnessed.

Nitrite (NO2) is added in small quantities to preserve and to color many cold cuts and hot dogs. At the time, acceptable limits for NO2 ranged for 100 to 150 ppm (mg of nitrite per kg of meat), depending on the product. But levels frequently surpassed the guidelines by 25 to 50%. At first I questioned my own analyses, but they were confirmed by my supervisor. The head of the lab said he would look into it at the production end, but weeks later the problem persisted. In general we were instructed not to carry out the analyses in duplicate, unless an anomalous result surfaced.

We had learned in the statistical math section of analytical chemistry that tests of the sort should be carried out in triplicate. One day an inspector from Health and Welfare Canada came into the lab, and I told him about the problem. He told me he was just a summer replacement with only a background in CEGEP ( a junior college) health sciences, and so that he could not really understand what I was saying. Later that summer, I was switched to the night shift, and I was alone in the lab. Digging into records from the previous two years, I found that other technicians had also been routinely finding high levels of nitrite (exceeding guidelines) in two specific products.

Nitrite, I realize, is an important preservative, and although it has been associated with cancer in rats, the “traditional” consensus is that the possibility of a similar occurrence in humans is only slightly elevated because of the concurrent addition of erythorbate and/or ascorbic acid. This prevents the formation of nitrosamines in the stomach’s acidic environment, the actual compounds with carcinogenic connections in animals. But I also saw the pale color of the hot dog mixture prior to nitrite addition, and it would not have been so pale if the ingredients weren’t such a mishmash of intestines and other meat “scraps”.

hotdogs_insideMost of the public was unaware that what they were really tasting in hot dogs were the strong spices, salt and sugars. Our analyses revealed that the fraction of dextrose in hot dogs ( close to 10%)  was routinely greater than that of protein, placing the product somewhere on the spectrum between meat and candy. (Currently, according to USDA analyses, things are better from that perspective. The ratio of protein to sugar in a 100 gram sample ranges from 6 to 10 grams of protein to 1 gram of sugar. Yet fresh meat or fish has triple the amount of protein.) Their ham was also adulterated with water, which then facilitated the growth of bacteria, thus increasing the need for nitrite additives. Even today processed ham is still diluted, slicing the protein level to half of what it should be.

When working there, I was strongly tempted to become a whistle-blower and to go public with what I thought were outrageous company practices from both a health and scientific standpoint. But relatives and friends were not supportive, and I was too wimpy to act alone. Aside from writing this piece, I have told my story to hundreds of students in my career, and since those analyses, I don’t think I’ve eaten more than a couple of meat-hot dogs in the last three decades.

A Journal of the National Cancer Institute study in 2005 found a link between processed meats and pancreatic cancer, but in fairness,the study did not prove that the risk was to the presence of nitrites. In recent years, Maple Leaf has used celery extract, which is rich in nitrites as a way of deceiving consumers into thinking they are buying a healthy alternative.

Defenders of nitrite in processed meats like to point out that lettuce and spinach can also have elevated levels of nitrate (which can be converted in to nitrite). There are two problems with their argument:

(1) Not all samples have concentrations comparable to nitrite levels. If the lettuce and spinach is not grown with fresh manure or with synthetic fertilizer, the nitrate levels plummet.

(2) The argument is akin to the nuclear industry’s old trick of attempting to abate fears about radiation wastes by pointing out that there are already natural radioactive isotopes in the earth’s crust and in our bodies. In both cases, what they are hiding is that by artificially increasing the background concentrations they are increasing the risk of complications.

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