Advanced Topic: Heavy Metals - Cadmium

Advanced Topic: Heavy Metals - Cadmium

cadmium In the Undoctored program, we adhere to the philosophy of restoring the human body to its natural state by addressing modern factors that have disrupted it, a practice that reverses numerous common chronic diseases. We don’t “treat” health conditions, but address the factors that allow diseases to emerge in the first place, a much more powerful approach.


Let’s now concentrate on the accumulation of heavy metals that are largely a product of modern industrial life. Exposure and accumulation of potentially toxic heavy metals are not an issue for everyone in the Undoctored lifestyle, but a select few under specific circumstances. It is also worth being aware of the many strategies we can easily adopt that prevent accumulation of these metals. 

Cadmium is ubiquitous, as it is naturally present in soil, water, rocks, and minerals as various salts such as cadmium oxide, cadmium chloride, and cadmium sulfide. Starting with the Industrial Revolution, worldwide industrialization with activities such as mining, smelting, coal burning, production of cadmium batteries, use as a plastic stabilizer in polyvinyl, pigments, use of phosphate fertilizers and other products has mobilized this mineral from its natural stores and thereby increased ambient cadmium levels in the environment. Urban and industrial areas have increased particulate matter in the air that contains cadmium, with as much as 200-fold greater levels than remote or rural levels.

Excessive human exposure to cadmium primarily occurs through inhalation from cigarette smoking and workplace exposures. The greatest risk of cadmium exposure occurs in cigarette smokers (as the tobacco plant uptakes soil cadmium) who have three-fold greater levels in various tissues.

Cadmium is also ingested through food and gastrointestinal absorption. Gastrointestinal absorption is less efficient than inhaled exposure, with only 5-10% of ingested cadmium absorbed into the body. Plants consumed by humans, as well as consumption of animal products from livestock that graze on grass and forage, contain cadmium. For most of us who do not smoke cigarettes or work in industries involving cadmium exposure, simply eating food exposes us to some quantity of cadmium. While drinking water can contain cadmium, the quantity is usually low (unless in an industrially contaminated area).

Once it gains entry into the body, cadmium is excreted via urine and bowels. But its clearance is exceptionally slow, persisting in the body for decades after exposure. Its long-term persistence means that continued exposure allows accumulation and levels of cadmium in the body therefore generally increase as we age.

While the evidence is observational and therefore cannot conclusively establish a cause-effect relationship, populations with greater cadmium exposure appear to have higher incidences of cancer and cardiovascular disease. The International Agency for Research on Cancer designates cadmium as a group I human carcinogen. Cadmium has been associated with cancers of the lung, breast, prostate, pancreas, urinary bladder, uterus, nasopharynx, and non-Hodgkin’s lymphoma. Cadmium exposure is also a potential cause of hypertension, kidney disease, benign prostatic hypertrophy, and osteoporosis. The presence of cadmium has been documented in nearly every organ and tissue of the body in modern people.

Beyond cigarette smoking, other factors that have been associated with greater cadmium exposure and potential for toxicity include:

  • Farm work—Use of phosphate fertilizers has increased cadmium exposure for farmers, as well as increased soil cadmium content several-fold.
  • Work in industries involving manufacture of batteries, plastics, coatings, solar panels, spray paints used to paint automobiles, and exposure to landfill, electronic recycling, and plastic recycling
  • Welding and soldering—a source of inhalational exposure
  • Consumption of oysters and other shellfish (63% higher serum levels, 24% higher urinary levels)
  • Consumption of kidney, a concentrator of body cadmium
  • Oddly, females accumulate cadmium more than males, having 30-80% higher tissue levels (an effect at least partly due to lower iron status, as iron blocks intestinal cadmium absorption)
  • Wheat and grain consumption present among the greatest exposures to the oral ingestion of cadmium.
  • Vegetarians have three-fold higher cadmium intake, since 70-80% of dietary cadmium intake comes through plant-based foods.
  • Low iron status (e.g., lower ferritin levels and iron deficiency anemia) are associated with higher levels of cadmium in otherwise healthy females.
  • Forest fires—as those occurring on the Pacific coast of the U.S.
One of the most informative recent insights surrounding the effects of cadmium came from a study of children chosen to be representative of the U.S. population, not selected for cadmium exposure. Surprisingly, urinary cadmium levels were closely associated with likelihood of learning disabilities and need for special education, including at urinary cadmium levels previously believed to be benign. This has caused experts to regard cadmium as toxic as lead, with children being especially vulnerable to the neurotoxic effects. (The highest quartile with urinary cadmium levels that ranged from 0.18 to 14.94 micrograms per liter (μg/L) had more than a three-fold greater likelihood of experiencing a learning disability.) Of course, these children were not cigarette smokers, nor did they work in industries that risked cadmium exposure, but were presumably exposed through environmental and food exposure.

Because cadmium persists for many decades in the human body, its prolonged persistence means that cadmium tends to accumulate with repeated chronic exposure. Cadmium is cleared from the blood, however, over 75 to 128 days. Blood levels are therefore only reflections of recent exposure over the preceding year. According to the U.S. Department of Health and Human Services Agency for Toxic Substances and Disease Registry, the mean level of cadmium in the blood in the U.S. is 0.315 micrograms/L. Because the kidney contains 30-50% of the entire body’s burden of cadmium, urine cadmium levels are the most reliable gauge of exposure. In urine, mean levels are 0.193 micrograms/gram of (urinary) creatinine or 0.185 micrograms/L. While blood levels tend to reflect only recent cadmium exposure, urine levels therefore better reflect kidney and total body burden and long-term exposure.

Exposure to cadmium during early life has been associated with greater potential for adult obesity, likely via an epigenetic mechanism (i.e., not involving a change in genetic code, but in the proteins that regulate genetic expression). A number of analyses have been performed to determine whether cadmium exposure increases risk for metabolic syndrome, type 2 diabetes, and obesity. However, results have been conflicting and no firm relationship has emerged.

Cadmium has been found to alter the composition of the intestinal microbiome, reducing species diversity and reducing populations of several butyrate-producing species. Intestinal lipopolysaccharide (LPS) levels are also increased, coupled with deterioration of the intestinal barrier, a combination that increases endotoxemia. Emerging evidence suggests that higher levels of cadmium (>0.96 μg/L for men and >1.28 μg/L for women) in the blood are associated with both increased LPS blood levels and metabolic syndrome.

Testing should be considered if there is a history of cigarette smoking or substantial secondary smoke exposure; exposure to high-risk settings, e.g., working as a welder, spray painting autos, burning municipal trash; a history of chronic anxiety or depression; unexplained fatigue; infertility; loss of memory; any evidence for reduced kidney function or unexplained proteinuria (protein in the urine); osteopenia or osteoporosis.

The FDA’s Toxic Element Working Group has been working to educate farmers, agribusiness, and selected manufacturers on methods to mitigate cadmium levels in food and workplaces, efforts that will take many years for widespread implementation. In the meantime, personal efforts to minimize exposure and ingestion of cadmium are worth being aware of.

What levels of cadmium pose health dangers?

As with a number of other toxic chemicals, the safe level of exposure has been progressively updated over the years, as evidence of cadmium’s toxicity at lower levels than expected has emerged. The latest analyses suggest that a safe level of intake is <30 μg/day, a level that may produce adverse kidney effects in about 1% of the adult population.

The USDA has performed detailed analyses of the cadmium content of various foods. Among the highest cadmium content has been found in (mean values shown; 1 kg = 2.2 pounds):

  • Liver (beef/calf) 56 μg/kg
  • Peanut butter 39
  • Peanuts, dry roasted 44
  • Whole wheat bread. 25
  • Shredded wheat cereal 54
  • Spinach 183
  • Lettuce, iceberg 51
  • Celery 36
  • Potato chips 54
  • Sunflower seeds. 389

In separate analyses, filter-feeding shellfish such as oysters, scallops, and mussels have been found to pose increased potential for cadmium toxicity, although controversy exists over the bioavailability of natural vs. industrially-sourced cadmium. Nonetheless, in one analysis, consuming high intakes of shellfish was associated with mean cadmium intakes of 28 μg/day with 24% of people showing increased urinary cadmium levels if iron deficiency was present.

A detailed analysis of cadmium ingestion from food in a broad sample of the American public showed:

Cadmium in Foods

Cocoa products can also contain high levels of cadmium, according to both the USDA (no brands specified) and Consumer Lab (brands specified), with the highest and potentially toxic levels uncovered in cocoa powders, especially products sourced from South America (but not Africa). Some dark chocolate bars also have exceptional levels of cadmium, such as Trader Joe’s Dark Chocolate Lover’s Chocolate Bar with 29 μg in a 40 g bar, Pascha Organic Dark Chocolate 22.7 μg per 42 g bar, Scharffen Berger Unsweetened with 13.6 μg per 55 g bar, and Dove Dark Chocolate with 9.5 μg per 40 g bar. Most other dark chocolates have 2-7 μg per bar.

Dietary assessments that estimated daily cadmium intake by using USDA data suggests that most American adults ingest approximately 5 μg/day. Earlier studies suggested a higher intake of 10.9 μg/day, suggesting that dietary intake in Americans may have declined in recent years. Urinary cadmium levels have also been noted to decline by 34% between the periods of 1988-1994 and 2003-2008, which has been speculated to reflect declining numbers of people smoking cigarettes, the result of some state legislation limiting use of phosphate fertilizers containing cadmium, and regulation over industrial air- and water-polluting activities.

Urine and blood are therefore the preferred methods of assessing cadmium status. Hair and finger- or toenails can also be used. Urine is the preferred method to assess long-term total body cadmium, while the others tend to reflect cadmium exposure over the previous several months. A 24-hour urine collection is the gold standard for cadmium measurement, although a first-morning urine specimen is also a reliable method.

Cadmium measures are often combined with measurement of a protein, beta-2-microglobulin, in the urine that can serve as an index of kidney damage from cadmium, along with serum creatinine (not the urine creatinine listed below). The U.S. Department of Labor suggests these interpretive guidelines for safe levels of cadmium:

Cadmium, Blood Less than or equal to 5.0 µg/L Cadmium, Urine - per volume 0.0-1.0 µg/L Cadmium, Urine - ratio to creatinine 0.0-3.0 µg/g CRT Beta-2-Microglobulin, Urine 0-300 µg/L Beta-2-Microglobulin, ratio to creatinine 0-300 µg/g creatinine

Most non-smoking adults not exposed to workplace cadmium have blood levels less than 5.0 µg/L.

Due to the lack of precise outcome data, there are no threshold values established that informs us over whether specific remedial action should be taken. In other words, if a urine specimen yields a cadmium value of 3.0 µg/L with a beta-2-microglobulin urine level of 290 µg/L, will this person gain any health benefit by achieving a lower level via, say, chelation? This has not yet been established.


A practical approach to minimizing cadmium exposure

Complete avoidance of cadmium is not possible, but we can minimize exposure to cadmium mobilized by human activity. Beyond obvious efforts such as not smoking cigarettes, avoiding secondary smoke, and taking precautions in any potentially contaminated workplace environment, among the practical steps you can take to minimize exposure to cadmium are:

  • Eliminate wheat and grains—Excluding wheat and grains from the diet eliminates the dominant source of dietary cadmium for most people. It also eliminates exposure to phytates that bind iron, zinc, magnesium, and calcium that compete with cadmium for absorption. Without phytates, minerals are able to block absorption of cadmium.
  • Ensuring adequate intakes of iron, zinc, calcium, magnesium, and selenium—as these minerals compete with cadmium for absorption. Experimental evidence suggests that even marginal deficiencies can increase intestinal cadmium absorption 10-fold. Having adequate levels of iron, zinc and magnesium are especially important to inhibit absorption of cadmium. (These minerals do not reduce kidney or body levels of cadmium, but only inhibit absorption due to ongoing exposure from oral ingestion.)
  • Choose organic produce—that has been shown to have 48% lower cadmium content.
  • Sweating—Sweating has been demonstrated to be an effective means of excreting cadmium and other toxic compounds such as lead, phthalates, and bisphenol A. Use of a sauna is one means of increasing sweat production that has been shown to be effective.
  • Ironically, people who exercise at high levels develop higher serum and urine levels of cadmium, as well as arsenic and lead. The cause for this is unclear but may involve the greater consumption of air, water, and food obliged by high physical activity.
  • Supplementation with Lactobacillus plantarum CCFM8610 has been shown to increase stool cadmium by more than 70% and thereby reduce tissue levels substantially over 8 weeks. However, it is not clear whether this is a strain- or species-specific property. Lesser degrees of cadmium removal can be achieved with L. reuteri, L. bulgaricus, L. rhamnosus GG, and Bifidobacterium bifidum.
  • Minimize use of cocoa powders and selected high-cadmium chocolates sourced from South America (listed above). Key may be to consume brands with lower cadmium levels and in only small amounts and not habitually.
Modified citrus pectin (PectaSol), i.e., food-sourced pectin fibers that are exposed to pH and enzymatic modification to cause fragmentation of the large pectin molecule, 15 grams per day, has been shown to increase urinary clearance of cadmium, as well as lead and arsenic. In its native form sourced from the pith of citrus fruit, pectin fiber is unabsorbable but metabolized by intestinal microbiome species. Modification of the pectin molecule therefore allows intestinal absorption of pectin fragments into the bloodstream with evidence suggesting substantial kidney clearance of heavy metals results.

Intravenous (IV) chelation with various chelating substances such as EDTA can also be undertaken, but should only be conducted by practitioners with experience with these agents, as there are multiple variables to factor in, such as dose, frequency, use of glutathione and other agents to reduce risk of kidney toxicity, need for supplemental minerals depleted during chelation efforts. Failure to do so in past has led to several fatal events. Preliminary evidence from the TACT Study of intravenous EDTA demonstrated a modest reduction in cardiovascular events, especially in people with type 2 diabetes, but effects were not correlated to measures of heavy metals (although it is primarily lead and cadmium that are removed with EDTA chelation). The ongoing TACT II will address this question. Because blood and urine levels have not been correlated with toxicity, IV chelation should only be undertaken when there is an identifiable history of cadmium exposure, e.g., work in an industrial setting known to involve cadmium, habitual consumption of shellfish, smokers. While chelation has been demonstrated to yield benefits to manage acute toxicity, there are insufficient data to support use of chelation to improve health outcomes with chronic toxicity.

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Advanced Topics: Heavy Metals - Cadmium

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