Transcript: Cadmium and Cancer: Plant vs. Animal Foods
Cadmium is known as a highly toxic metal that represents a major hazard to human health. It sticks around in our body for decades because our body has no efficient way to get rid of it, and may contribute to a variety of illnesses, including heart disease, cancer, and diabetes. Most recently, data suggests that cadmium exposure may impair cognitive performance even at levels once thought to be safe.
Recent studies suggest cadmium exposure may produce adverse health effects at lower exposure levels than previously predicted, including increased risk of hormonal cancers. For example, researchers on Long Island estimated that about 40% of breast cancer in the U.S. might be associated with elevated cadmium levels.
Inhalation of cigarette smoke is one of the major routes for human exposure to cadmium. Seafood consumption is another dominant route of human exposure in this study even more so than cigarette smoke. The highest levels, though, are found in organ meats, but how many horse kidneys can you eat? Because people eat so few organs, grains and vegetables actually end up contributing the largest amount.
But wait a second, whole grains and vegetables are among the major dietary sources of fiber, phytoestrogens, antioxidants that may protect against breast cancer. And indeed, even though the risk of breast cancer goes up as women consume more and more cadmium, even though on paper, most cadmium comes from grains and vegetables, breast cancer risk goes down, the more and more whole grains and vegetables women eat, so maybe the animal-sourced cadmium is somehow worse, or the benefits of plant foods just overwhelm any adverse effects of the cadmium?
This study may have helped solve the mystery. It’s not what we eat, it’s what we absorb. Cadmium bioavailability from animal-based foods may be higher than that from vegetable-based foods. There appears to be something in plants that inhibits cadmium absorption. In fact, if you add kale to your boiled pig kidneys, you can cut down on the toxic exposure. Just one tablespoon of pig kidney and we may exceed the daily safety limit—unless you add kale, in which case you could eat a quarter cup. The pronounced effects of the inhibitory factors in kale point out the importance of vegetable foods in terms of prevention of health hazard from cadmium ingested as mixed diets in a real situation.
Even if a vegetarian diet contains more lead and cadmium than a mixed diet, it is not certain that it will give rise to higher uptake of the metals, because the absorption of lead and cadmium is inhibited by plant components such as fibre and phytate. And it’s not just in lab animals. Having whole grains in our stomach up to three hours before we swallow lead can eliminate 90% of absorption, thought to be due to phytates in whole grains, nuts, and beans grabbing onto it.
So vegetarians may have lower levels even though they have higher intakes. In fact, a significant decrease in the hair concentrations of lead and cadmium as seen after the change from an omnivorous to a vegetarian diet, indicating a lower absorption of the metals. Here’s that study. They took folks eating a standard Swedish diet and put them on a vegetarian diet. Lots of whole unrefined plant foods, no meat, poultry, fish, eggs, with junk food discouraged. Here’s where they started out, a measure of their mercury levels, cadmium levels, and lead levels in their body. Within three months on a vegetarian diet, their levels significantly dropped, and stayed down for the rest of the year-long experiment. But then they came back three years later, three years after they stopped eating vegetarian. And what did they find? Their levels of mercury, cadmium and lead shot back up.
Since the cadmium in plants is based on the cadmium in soil, plant-eaters that live in a really polluted areas like Slovakia, which has some of the highest levels, the so-called black triangle of pollution, thanks to the chemical and smelting industries. Those who eat lots of plants there can indeed build up higher cadmium levels, especially if you eat lots of plants. It’s interesting, in spite of the significantly higher blood cadmium concentration as a consequence of a greater cadmium intake from polluted plants all the antioxidants in those same plants were found to help inhibit the harmful effects of higher free radical production caused by the cadmium exposure. Still, though, in highly polluted areas it might be an especially good idea not to smoke, or eat too much seafood or organ meats, but even if we live in the Slovak Republic’s black triangle of pollution, the benefits of whole plant foods would outweigh the risks. In highly polluted areas, zinc supplements may decrease cadmium absorption, but I’d recommend against multi-mineral supplements, as they have been found to be contaminated with cadmium itself.
To see any graphs, charts, graphics, images, and quotes to which Dr. Greger may be referring, watch the above video. This is just an approximation of the audio contributed by Katie Schloer.
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