Tofu May Get the Lead Out

Lead, a toxic heavy metal, can show up in the most unexpected places. For instance, several recent studies documented a worrisome tainting of calcium supplements. Just last month, some Mexican lollipops were recalled from U.S. stores upon a finding that their wrappers had leached lead into the candy. And recently, this column recounted the perils of a man poisoned by his bathtub winemaking operations.

Of course, people can be exposed to lead through more obvious means–by breathing fumes in metalworking plants, eating foods tainted by emissions from cars burning leaded gasoline, exposure to peeling lead-based paint, or drinking water that enters homes through lead-soldered pipes.

A new study finds that for people who cant avoid such lead exposures, there may be a simple means to limit the bodys uptake: Eat tofu.

Lead and calcium

To the body, lead looks much like calcium. Indeed, thats why the body stores much of its lead in bone.

Previous studies have shown that children who dont get sufficient calcium in their diet tend to accumulate more lead from their environment than do calcium-sufficient youngsters. This has led to the suspicion that making sure children get a bounty of calcium–from milk, cheese, and even supplements–might be a way to discourage the bodys uptake of any lead. Experiments to actively explore that possibility are now underway.

In the meantime, Changzhong Chen of the Harvard School of Public Health and his colleagues have data from what is essentially an unintentional test of that same hypothesis.

They evaluated newlyweds in two Chinese regions, residential Dadong and industrial Tiexi. In both communities, lead exposures tended to be high–usually tainting the blood at 10 to 13 micrograms per deciliter, or five to seven times the concentrations typically seen in U.S. adults.

Many people in these surveyed regions–but by no means all–also down plenty of tofu. This soybean curd is usually produced by treating soy mash with calcium salts, resulting in a product rich in calcium.

Chens group suspected the people eating large amounts of tofu would take in enough calcium to reduce their lead uptake.

As part of a larger study, the researchers conducted physical exams of all 1,155 participants, which included quantifying the amount of lead in their blood. Each man and woman also filled out a detailed dietary questionnaire that probed, among other things, how much tofu he or she typically consumed.

In the June 15 American Journal of Epidemiology, the team now reports finding that among these young adults, lead tainting fell as tofu consumption rose.

Tofu consumption

The epidemiologists divided the volunteers into four groups on the basis of how much tofu they ate. The lowest group consumed less than 250 grams per week (anything up to almost 9 ounces), the highest group regularly devoured 750 grams or more (at least some 1.7 pounds).

For each successive group of increasing tofu consumption, average blood lead concentrations dropped 3.7 percent, or about 0.5 micrograms per deciliter. In other words, those regularly consuming the most tofu had blood lead levels 11.3 percent lower than those in the lowest-tofu group. Moreover, this association held up even after adjusting the statistics to account for potentially confounding variables, such as smoking, alcohol intake, occupation, and other dietary-consumption patterns.

Indeed, the scientists report, the study results are robust and consistently demonstrate a dose-response relation between tofu intake and blood-lead level.

Does this prove tofu made a difference? Of course not. However, Chens team observes, because tofu tends to have plenty of calcium and phytic acid–another nutrient that studies have suggested may impair lead uptake– it is biologically plausible that tofu may inhibit lead absorption and retention, thus reducing blood-lead levels.

Brain function

Why care about lead?

In children, it can impair brain function, actually diminishing IQ. Much of the lead that a baby will encounter during its most vulnerable months comes from Mom–either in the womb or via breast milk. And because lead gets stored in bone, the body holds it until bone is dissolved–either to obtain the calcium needed to nourish a child, or during our much later years, when exercise diminishes and osteoporosis develops.

Even in early middle age, many people appear to suffer from lead in the body. A host of studies in men have shown that as lead concentrations in the blood rises, blood pressure subtly climbs too, increasing the risk of heart disease and stroke.

So, people should be wary about lead and do their best to limit its uptake.

But think youre not the tofu type? There may be a chocolatey solution. Try the recipe for Janet’s Chocolate Medicinal Mousse Pie (see Chocolate Therapies (with Recipe for Janet’s Chocolate Medicinal Mousse Pie)). Even my dad, who would never knowingly let a forkful of soy pass his lips, loves this dessert. Sshhh. Dont tell him, but its main ingredient is tofu.

Janet Raloff is the Editor, Digital of Science News Explores, a daily online magazine for middle school students. She started at Science News in 1977 as the environment and policy writer, specializing in toxicology. To her never-ending surprise, her daughter became a toxicologist.

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