Health educators and toxicologists make us believe that nitrate is bad for health. However, more and more research is countering this statement. Nitrate would benefit heart health and help maintain a healthy blood pressure.
Published in: EOS magazine 10, 2009 (in Dutch: Is nitraat gezond?- pdf)
The nitrogen compound nitrate is naturally present in soils. However, during the last decades its concentrations have increased considerably, as a result of the application of animal and artificial manure in agriculture. Vegetables and fruit accumulate nitrate from soils. The remaining soil nitrate is washed away towards drinking water supplies. Next to drinking water and food, humans can also ingest nitrate from eating meat, but according to the European Food Safety Authority (EFSA) half to two thirds of human nitrate ingestion stems from vegetables and fruit.
All vegetables contain nitrate in different degrees. Nitrate uptake is thus more dependent on what types of vegetables you eat and less on how many vegetables you eat daily. Green leafy vegetables – such as spinach, rocket salad and lamb’s lettuce – are known to be high in nitrate. The amount of manure applied and available sunlight during growth are also important factors determining the nitrate content of vegetables. Vegetables from Northern Europe obtain less sunlight than Southern-European vegetables and as a result contain more nitrate.
Blue babies and cancer
From time to time, the media reports that nitrate is toxic and that we should limit our intake of spinach, rocket salad, lamb’s lettuce and other vegetables rich in nitrates. High nitrate intake would cause cancer and induce oxygen deficit in babies. During the 50s, babies in the US suffered from oxygen deficit, the so called ‘blue baby syndrom’, after drinking water from nitrate rich wells. Upon ingestion nitrate can be converted into nitrite. Nitrite can react with hemoglobin, the oxygen transporting protein in our blood, forming methemoglobine, thereby preventing oxygen transport and inducing oxygen deficit. ‘But later it was found that not nitrate caused the oxygen deficit, but that bacteria present in the water from wells are to be blamed,’ says professor Katan from Amsterdam University. ‘Nitrate in well water is not the culprit, as long as the water is not contaminated with bacteria.’ But blue baby syndrome led the North-American Environmental Protection Agency (EPA) to define strict norms for the concentration of nitrate in drinking water (44 mg/l). In Flanders and The Netherlands, the norm is set at 50 mg nitrate per liter of drinking water. These norms mean that farmers are limited in the amount of manure they can place on their farmland. In 1962, the World Health Organization (WHO) announced norms for the concentration of nitrate in food. The norm was set at 3.7 mg nitrate per kg body weight, for a person of 60 kg this would be 222 mg.
The second reason why nitrate is persecuted, is its hypothetical role in cancer. In the body nitrate can be converted into nitrosamine. It has been shown that this cancer-inducing compound is harmful to animals, but it is unclear if the concentrations we are exposed to, are harmful too. ‘It is about time that the persecution of nitrate ends,’ states professor Katan. ‘Cancer incidence, more specifically for stomach cancer, is lower in people that ingest a lot of nitrate than in people ingesting low amounts of nitrate. This is easily explained knowing that vegetables are our richest source of nitrate and that high vegetable consumption is correlated with a low incidence of cancer. The amount of nitrosamines that can be formed in our stomach from nitrate is probably too low to induce cancer. The conclusion is that the presumed relationship between cancer, and nitrate in drinking water and food is very weak.’
Benefits of nitrates
But there is more. ‘Some researchers believe that nitrate can help in the prevention of heart diseases,’ explains professor Katan. ’When one has heart problems, it is no use to eat a lot of spinach, but the doctor will prescribe medicines that contain nitrate. When putting the medicine under the tongue, nitrate is converted to nitrite and then to nitrogen oxide. Nitrogen oxide expands the blood vessels thereby lowering chest pressure. There are also indications that nitrate lowers blood pressure.’ According to professor Katan it is time that we investigate the relationship between blood pressure and nitrate in more detail.
Eat your vegetables
‘Health educators need to reevaluate the case of nitrate,’ states professor Katan. The evidence for negative effects of nitrate is scarce. Of course this is often the case for so called toxic compounds that are regulated by norms. The government is very careful whenever there is the slightest indication that a compound is toxic, and that is wise. However, the story looks completely different when that same compound has positive health effects.’
In 2008, the EFSA announced a statement on the risk of nitrate in vegetables: The potential risks of the uptake of nitrate do not outweigh the positive effects of a balanced diet rich in vegetables and fruit. When consumed in sufficient amounts, fruit and vegetables may decrease the risk of certain diseases. Persons eating the daily recommended 400 gram of vegetables and fruit do not cross the daily tolerable nitrate intake. A small proportion of the European population, some 2.5 percent, may cross the nitrate norm. According to professor Katan, the latter should not be a problem either. ‘A vegetarian eating green leafy vegetables daily, thereby crossing the norm for nitrate intake, should not fear negative effects of nitrate.’
A team of American scientists would like to take the nitrate issue one step further. They say nitrate is not only healthy, but should be considered a nutrient. Because nitrate is healthy at concentrations that now exceed the norm, the norm should be reestablished. ‘It is too early to revise the norm,’ says professor Katan. ‘First, we need more research on the role of nitrate in lowering of blood pressure. There is no need either to tell people to eat a lot of nitrate rich vegetables. But we do need to start the debate whether the present recommendations to limit the consumption of nitrate rich vegetables is still justifiable. At present we are scaring people, and as s result these people may miss the positive health effects of both vegetables and nitrate’.
- Katan MB, 2009. Nitrate in foods: harmful or healthy? Editorial. American Journal of Clinical Nutrition 90: 11-12.
- Hord NG, Tang Y, and Bryan NS, 2009. Food sources of nitrates and nitrites: the physiologic context for potential health benefits. American Journal of Clinical Nutrition 90: 1-10.
- EFSA (European Food Safety Authority), 2008. EFSA balances the consumer risks from nitrate in vegetables with the benefits of balanced diet high in vegetables and fruit. EFSAPress release.