Nitrate is part of the nitrogen cycle. It occurs in air, soil, water and food. Besides, it can also be produced by living organisms. Artificial use of nitrates is mainly for preservation, such as in cheese and its product, as well as in processed meat (e.g. ham). Nitrate itself is relatively non-toxic, but it can be metabolized to nitrite in the body. Nitrite may cause adverse health impact, such as cancers.
The Joint Food and Agriculture Organization (FAO)/ World Health Organization (WHO) Expert Committee on Food Additives (JECFA) in 2002 has set the ADI (acceptable daily intake) of nitrate to be 3.7 mg per kg body weight. In other words, a 60 kg adult can take in 222 mg of nitrates per day.
A large proportion of human exposure to nitrate is through the consumption of vegetables, whereas contaminated drinking water, processed meat, milk as well as their products may also make up part of the contribution. The amount of nitrates in vegetables varies among the species, the edible portion, growing season, intensity of light, temperature, fertilizers, storage and processing. For example, broccoli and eggplant contain relatively less nitrates, while the level of nitrates in spinach and amaranth is relatively high. Herbs also contain a high level of nitrates (average 1240 mg/kg). However, the amount of herbs consumed is generally low and its effect will be comparatively less.
The average level of nitrates in vegetables
|
Species |
Reported level (mg/kg) |
|
Amaranth |
2167 |
|
Lettuce |
1324 |
|
Spinach |
1066 |
|
Celery |
1103 |
|
White radish |
1416 |
|
Beetroot |
1379 |
|
Cabbage |
933 |
|
Pumpkin |
894 |
|
Broccoli |
279 |
|
Cauliflower |
311 |
|
Onion |
164 |
|
Garlic |
69 |
|
Tomato |
43 |
|
Mushroom |
61 |
|
Peas |
30 |
Even though vegetables contain nitrates, they provide us with plenty of dietary fiber, vitamins and minerals, which are crucial for human health. The European Food Safety Authority has evaluated the risks of exposure to nitrates from vegetables. Their conclusion was “overall, the estimated exposures to nitrate from vegetables are unlikely to result in appreciable health risks, therefore the recognized beneficial effects of consumption of vegetables prevail”. The public should maintain a balanced diet, and avoid overindulgence of specific foods.
Safety tips to the public
1. Maintain a balanced diet, and consume a large variety of fruits and vegetables.
2. Washing, peeling and cooking can reduce the risks of exposure to nitrates from the vegetables.
3. Vegetables should be kept in the refrigerator.
Safety tips to the industry
1. Food should be obtained from reliable sources.
