Eat a lot of salad and green veggies? You might not be as healthy as you think you are, especially if you eat leafy vegetables grown in Taiwan.
The safety of fresh produce has been questioned in light of a widely publicized case in the media earlier this month, in which a 42-year-old Taiwanese woman developed acute methemoglobinemia, a disorder in which blood can’t transport oxygen because of reduced levels of hemoglobin.
Also known as “blue baby syndrome,” methemoglobinemia tends to affect infants and is commonly caused by excessive amounts of nitrates in ground water. But in the case of the woman, her doctor, Chiang Shou-shan (江守山), thinks a vegetarian diet was the culprit.
Photo: Noah Buchan, Taipei Times
Chiang, a nephrologist (a doctor who specializes in kidney and liver functions) at Shin-Kong Wu Ho-Su Memorial Hospital, says he suspects the woman’s “habit” of eating leafy vegetables may have exposed her to excessive levels of nitrates.
Nitrates are a naturally occurring substance — it’s a form of nitrogen — and are not harmful in and of themselves. Plants rely on them for nutrients.
But Chiang says the problem is that nitrates are being found in excessive amounts in Taiwan, and this has to do with the overuse of nitrogen-based fertilizers, both in organic and non-organic farming. Vegetables grown in winter or harvested in darkness — most vegetables sold in both markets and supermarkets are picked at night or before dawn to maintain freshness — tend to have higher levels of nitrates, he says.
Chiang says the problem is compounded by the fact that Taiwanese consume more leafy vegetables than other countries.
So how worried should we be about nitrates? It depends on who you ask.
The Homemakers United Foundation (主婦聯盟環境保護基金會), an environmental and health issues NGO, shares his concern about nitrate levels. The group, which consults with agriculture and horticulture experts from National Taiwan University, started to speak out on the issue several years ago.
The group periodically conducts its own tests on nitrate levels in vegetables and has been waging an ongoing public education campaign to call attention to what it says are potential health hazards.
Homemakers United says the general public should be wary of nitrates because of their potential to convert into a toxic substance. Once ingested, nitrates have the potential to convert into nitrites. When nitrites combine with amino acids in the stomach, they become nitrosamines, a compound associated with the risk of cancer. Cured or smoked meats, particularly bacon, have been found to contain nitrosamine, which can form because nitrates and nitrites are used in the curing process.
The government has mandated limits on nitrites in smoked meats, but no limits on fresh produce. Homemakers United has been lobbying the Council of Agriculture (COA) to implement similar safety standards for leafy greens used by the European Union, which has limits on nitrate levels for spinach and lettuce.
The COA’s Agriculture and Food Agency, which oversees safety regulations for the nation’s farming industry, says there is no need for such limits in Taiwan. The agency has been engaged in a back-and-forth exchange with Homemakers United through press releases.
What’s the standard?
The Agriculture and Food Agency’s argument against setting limits on nitrates on fresh produce has been that the World Health Organization (WHO) has no such limits, nor do the US, Japan, Canada and Australia. (The WHO does have a general limit on nitrate intake per person — 3.7 mg of nitrate per kg of body weight, but not on specific foods.)
In a press release last week, the agency said there is “no definitive evidence that shows nitrates from vegetables will convert into nitrites or nitrosamine after being consumed,” and adding there are “no clear risks to health after consuming nitrates from vegetables,” citing an EU Food Safety Authority report.
But Homemakers United says Asian dietary habits need to be taken into account, echoing Chiang’s assertion that Taiwanese, on average, tend to eat more leafy greens than people in Western countries.
The group released a FAQ sheet that includes a way to calculate one’s daily nitrate limit based on the WHO’s recommendation of 3.7mg per kg of body weight. For example, if you weigh 60 kg, then your daily limit of nitrate would be 222 mg (3.7 times 60kg/your weight times 3.7). A “safe” amount of vegetables for consumption would depend on the level of nitrate found in the food, a factor that can only be known through testing.
While Homemakers United does not explicitly encourage people to test their vegetables, one of its consultants, Lin Bi-hsia (林碧霞), a retired academic who has a PhD in horticulture from National Taiwan University says she recommends that people test their vegetables using inexpensive strip test kits, which cost around NT$150 for 10 tests.
Chiang, the Shin Kong Hospital doctor, also recommends testing, and says he has developed a patented nitrate test for vegetables.
But asking average consumers to measure the nitrate levels in their own vegetables is an overreaction, says Lin Ja-liang (林杰樑), director of clinical toxicology at the Chang Gung Memorial Hospital.
The doctor, who also serves as a professor of nephrology at Chang Gung University, casts doubt on the case of the woman who is suspected of becoming ill from eating too many leafy greens.
“I’ve never heard of a case of in which a person suffered poisoning from eating too many vegetables,” Lin Ja-liang said. “In my professional opinion, I don’t believe that this is possible in this case.”
He stresses that the real area of concern is nitrites and nitrosamine, but Taiwan’s current limits on nitrites in food are “safe,” he says.
The raw and the cooked
And even then, Lin Ja-liang thinks there’s little reason to worry. “On average, when nitrates become nitrites, the resulting amount is very small,” he said. “The liver and kidneys can metabolize nitrites because the amounts that occur are usually very small.”
The Taipei Times asked for his opinion on a report by Homemakers United that found that test samples of leafy vegetables purchased at various markets had contained as much as 20,000ppm of nitrates (see page 5, Sept. 12, 2012 of the Taipei Times). By comparison, the EU’s limits on nitrates for spinach and lettuce are between 2,000 to 4,500mg per kg, with those figures varying from country to country.
Lin Ja-liang says such figures are not a cause for alarm because nitrate levels can be reduced easily by doing two simple things: washing and cooking the vegetables. Boiling a vegetable for one minute reduces nitrate content by one-third, while boiling for two minutes reduces nitrate content by half, he said.
Still, he thinks the EU standards are overkill, and reflect that Europeans are “overly worried” about the possibility of nitrates converting to nitrites. Lin Ja-liang also says that Taiwanese eat more cooked vegetables in comparison to Europeans, and thus are already reducing the nitrate levels.
Eat your veggies
But what if you do want to eat raw vegetables? Those who want to eat, for example, a salad from a convenience store every day, don’t need to worry either, Lin Ja-liang says, adding that we shouldn’t avoid leafy greens for fear of excessive nitrates. “The nutritional benefits outweigh the possible toxic effects.”
But Lin Bi-hsia, the NTU horticulture researcher, disagrees. She told the Taipei Times that washing and cooking vegetables to reduce nitrate content doesn’t go far enough to reduce the health risk, saying that nitrates can’t be completely removed from vegetables. A bigger worry, she said, was the long-term consumption of nitrates, which she believes to have negative health effects.
Lin Bi-Hsia and Lin Ja-liang do agree on one thing: the government needs to improve its safety standards and stop the overuse of fertilizers on Taiwanese farms.
At the moment, “nitrates” are a buzzword in health articles in Taiwanese media and on the Internet. The non-profit Consumers’ Foundation has also weighed in on the matter, joining Homemakers United in calling on the government to start nitrate testing for vegetables.
For Lin Bi-hsia, the need for testing is urgent. At a public forum held by Homemakers United, she gave a talk in which she compared the problem of nitrates to the issue of ractopamine in US beef products. The only difference between these issues, she said, was a matter of awareness.
“You don’t know about it, so you don’t pay attention to it. Farmers don’t know about it, so they don’t pay attention to it. Consumers don’t know about it, and don’t pay attention, so the government doesn’t know about it or pay attention,” she said.
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