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.
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.)