Nitrates in Leafy Greens

Nitrogen in Leafy Greens: Hazards and Health Benefits

Different foods contain enormous varieties of nutrients and minerals, essential to a long, healthy life. While growing up, children often hear about the need to have calcium for strong bones, Vitamin A for good eyesight, and iron for healthy blood. The lack of these essential nutrients leads to a host of other problems that, in developed countries, can easily be taken care of by good nutrition during childhood. Unfortunately, good nutrition may not be easy to come by in developing nations and the lack of essential nutrients is leading to widespread malnutrition and anemia among both children and adults. However, in some cases, too much of one mineral is consumed, leading to a whole other set of problems.  Nitrate, an essential compound for protein production, has been shown to be carcinogenic when overly ingested. Nitrate rich vegetables, such as leafy greens, are significant contributors to high levels of nitrate in the body.

Nitrogen, commonly found in nature as nitrite, nitrate, or ammonia, “enters the human body through drinking water, food and air. Ingested nitrates converted to nitrate” can lead to increased absorption of sodium, increased production of oxygen, and the dilation of blood cells (Gupta, 2008). Nitrate can react with amines and amides in the body, sometimes forming carcinogenic compounds, depending upon the pH level.  Low acidity favors the creation of these carcinogenic compounds, known as N-nitroso compounds. A toxic dose of ingested nitrate is around 2-5 grams, with reportedly lethal doses at 4-50 grams. Over consumption can result in acute toxicity symptoms, such as cyanosis, severe gastroenteritis with abdominal pain, blood in urine or feces, mental depression, and headache and weakness. Cancers associated with high nitrate ingestion include colon cancer, stomach cancer, and non-Hodgkin’s lymphoma. There is also a potential correlation between type-1 diabetes and high nitrate levels in drinking water, though more research on the matter is needed (Gupta, 2008).

            Fruits and vegetables account for 70% of the total nitrate intake, with drinking water accounting for 21%. Though “nitrate is present in most vegetables to a degree, the critical driver for a high-dietary exposure to nitrate is not the absolute amount of vegetables consumed but the type of vegetables, and the respective concentration of nitrate” (Anonymous, 2008). Spinach, lettuce and rucola, all leafy greens, have been found to have the highest levels of nitrate, but other factors, such as fertilizers, also affect concentration levels. Though these types of vegetables may increase levels of nitrates in the body, their health benefits appear to outweigh the risks. Spinach is high in iron and is often promoted as a ‘super-food’ in relation to nutritional value. In 2008, the European Food Safety Authority Contaminants Panel concluded that “the benefits of eating fresh produce outweigh any risk posed to human health from exposure to nitrate through vegetables,” finding only a small percentage of people eats enough leafy greens to actually experience negative effects (Anonymous, 2008).

            Though leafy greens have comparatively high levels of nitrates, how the vegetables are prepared is also an influential factor. According to the Department of Environmental Botany in New Delhi, India, “at least 50% of the nitrate can be removed by cooking vegetables in [low nitrate level] water” (Gupta, 2008). Also, avoiding aluminum pans and cooking utensils can significantly reduce nitrate levels in foods, as the aluminum “enhances reduction of nitrates to nitrite, and hence increases the toxicity” (Gupta, 2008). Washing, peeling, and cooking high nitrate level vegetables will generally reduce levels enough for continuous, safe consumption. Thus one should still be encouraged to consume these vegetables, as it is easy to reduce nitrate levels while still gaining other nutritional benefits.

            Certain farming practices may also reduce levels of nitrates in vegetables, allowing consumers to have even more confidence when picking which greens to cook. New Delhi’s Department of Environmental Botany recommends harvesting plants at noon time, as they have minimum levels of nitrate in the middle of the day. Also, the petioles of the plants show increased levels of nitrates as opposed to the broad, leaf surface. Therefore, removing the petioles could decrease nitrate levels in the vegetables when later sold to consumers. The most interesting method of decreasing nitrates in vegetables before it even reaches the consumers is monitoring and carefully selection genotypes “based on their relative levels of  nitrate content and nitrate reductase activity” (Gupta, 2008). Nitrate reductase is an enzyme that can significantly reduce nitrate accumulation in leafy vegetables. With an increasing number of technological solutions, as well as common, practical ones such as cooking vegetables in water, the threat of over consumption of nitrates through vegetables is fairly low, though other factors, such as contaminated drinking water, may pose a greater threat to human health.

            

References

Anonymous, (2008, July 3). Risk to Consumers from Nitrate found in Vegetables is Minimal.

            Horticulture Week, 36.

Gupta, S. K., Gupta, R. C., Chhabra, S. K., Eskiocak, S., Gupta, A.B., and Gupta, R., (2008).

            Health Issues Related to Nitrogen Pollution in water and air. Current Science, 94 (11),

            1460-1477.