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 also suggest that cadmium exposure may produce other adverse health effects at lower exposure levels than previously predicted, including increased risk of hormonal cancers. For example, researchers on Long Island estimated that as much as a third 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 route of human exposure. The highest levels, though, are found in organ meats. But how many horse kidneys do people eat? Since people eat so few organs, grains and vegetables actually end up contributing the largest amount to our collective diets.
However, don’t drop the salad from the menu yet.
Whole grains and vegetables are among the major dietary sources of fiber, phytoestrogens, and antioxidants that may protect against breast cancer. Indeed, even though the risk of breast cancer goes up as women consume more and more cadmium, and 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, are animal sources of cadmium somehow worse, or do the benefits of plant foods just overwhelm any adverse effects of the cadmium?
A study out of the Journal of the Medical Association of Thailand, highlighted in my video, Cadmium and Cancer: Plant vs. Animal Foods, 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, researchers found when they added kale to boiled pig kidneys, they could cut down on the toxic exposure. Just one tablespoon of pig kidney, and we may exceed the daily safety limit—unless we add kale, in which case we could eat a whole quarter cup. The pronounced effects of the inhibitory factors in kale point out, as the researchers note, “the importance of vegetable foods in terms of prevention of health hazard from [cadmium] ingested as mixed diets in a real situation.”
Researchers have concluded: “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 fiber and phytate.” 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 of lead and cadmium even though they have higher intakes.
In fact, there is a significant decrease in the hair concentrations of lead and cadmium after the change from an omnivorous to a vegetarian diet, indicating a lower absorption of the metals. Researchers took folks eating a standard Swedish diet and put them on a vegetarian diet. The vegetarians were encouraged to eat lots of whole, unrefined plant foods, with no meat, poultry, fish, and eggs. Junk food was also discouraged. Within three months on a vegetarian diet, their levels significantly dropped, and stayed down for the rest of the year-long experiment. The researchers came back three years later, three years after the subjects stopped eating vegetarian, and found that their levels of mercury, cadmium, and lead had shot back up.
Since the cadmium in plants is based on the cadmium in soil, plant-eaters that live in a really polluted area like Slovakia, which has some of the highest levels, thanks to the chemical and smelting industries, can indeed build up higher cadmium levels, especially if they eat lots of plants. It’s interesting that, “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. For people 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.
There are other toxins in cigarette smoke also found in food. See:
- Estrogenic Cooked Meat Carcinogens
- Heterocyclic Amines in Eggs, Cheese, and Creatine?
- Fukushima and Radioactivity in Seafood
Toxic metals have also been found in dietary supplements. See for example, Get the Lead Out and Heavy Metals in Protein Powder Supplements.
Mercury is also a serious problem. See:
- California Children are Contaminated
- Mercury vs. Omega-3s for Brain Development
- Nerves of Mercury
- Mercury in Corn Syrup?
More on pollution in seafood can be found in:
- Fish and Diabetes
- Diabetes and Dioxins
- Pollutants in Salmon and Our Own Fat
- Alkylphenol Endocrine Disruptors and Alleriges
- Dietary Sources of Alkylphenol Endocrine Disruptors
Michael Greger, M.D.
PS: If you haven’t yet, you can subscribe to my free videos here and watch my live year-in-review presentations Uprooting the Leading Causes of Death, More Than an Apple a Day, From Table to Able, and Food as Medicine.