A recent case in which a woman was hospitalized after feeling faint has been linked to the consumption of vegetables with high levels of nitrate
The woman developed acute methemoglobinemia, a disorder characterized by abnormal levels of oxidized hemoglobin in red blood cells that reduce the body’s ability to release oxygen to body tissues, after consuming vegetables that apparently contained high levels of nitrate.
Chiang Shou-shan (江守山), a nephrologist at Shin-Kong Wu Ho-Su Memorial Hospital, said the woman was rushed to the hospital for emergency treatment after suffering from severe dizziness.
Chiang said a medical examination confirmed that the woman had developed acute methemoglobinemia — which can lead to respiratory problems, unconsciousness and even death — as the oxygen in her hemoglobin had dropped sharply, turning her red blood cells light-blue.
“Judging from her eating habits, the woman might have developed the disorder after consuming vegetables with a high concentration of nitrates,” Chiang said.
Chiang said that more people are increasing their intake of vegetables while avoiding sausage and ham, because they think smoked goods contain nitrates, a substance that can be converted into nitrites in the human body, increasing cancer risks.
However, under certain circumstances, vegetables also contain excessive levels of such chemicals, Chiang said.
Both organic and chemical nitrogen-rich fertilizers commonly used for growing vegetables cause the plants to absorb high levels of nitrates, Chiang said, which are converted into protein molecules through photosynthesis.
However, with more vegetable farmers using nitrogen-rich fertilizer and more farmers harvesting their crops before daybreak to maintain freshness, Chiang said the nitrates in vegetables could build up in the human body, damaging health.
An inspection conducted by the Homemakers’ Union and Foundation in October 2010 on nitrate levels in seven types of vegetables found that leafy vegetables tended to contain higher levels of nitrates than root vegetables.
Some of the vegetables tested contained more than 20,000 parts per million (ppm) of the chemical substance — a level 10 times higher than the maximum international safety limit of 2,000ppm, the study showed.
“Theoretically, vegetables harvested before nightfall should not only be fresh, but also contain the least amount of nitrates. Yet that is only practical for home-grown vegetables,” Chiang said.
Customers should avoid vegetables grown using a lot of fertilizer, Chiang said, because the chemical traces, unlike chemical pesticides, cannot be washed off with water.
Chiang also urged farmers to change the time they harvest the vegetables to deliver vegetables that are both fresh and contain lower nitrate levels.