by Jack Norris, RD
Contents
Summary
Cadmium is a toxic heavy metal associated with osteoporosis, liver, and kidney disease. A study from the Slovak Republic, where cadmium levels in the soil are high, showed some vegans to have high enough blood cadmium levels to raise concerns. Correcting iron deficiency can prevent the body from absorbing cadmium. A modest zinc supplement is probably safe and could also reduce cadmium absorption as well as neutralize cadmium’s harmful effects in the body.
Background on Cadmium
The amount of cadmium in food is dependent on the amount of cadmium in the soil. It’s generally thought that undeveloped and developing countries have more cadmium in their soil. There have also been attempts to reduce the amount of cadmium in the environment in the United States by containing hazardous waste (Tellez-Plaza, 2012 (a)).
Cadmium is a common heavy metal found in soil due to the use of phosphate fertilizers (Krajcovicová-Kudládková 2006). Cadmium has a long biological half-life and it can take 30 years for the body to rid itself of it (Chakraborty 2013). Cadmium toxicity can cause painful osteoporosis, reduced kidney function (Chakraborty 2013), and liver toxicity (Krajcovicová-Kudládková 2006). Smokers tend to have higher cadmium levels due to high levels in tobacco.
Blood cadmium levels as low as 0.5 to 0.8 µg/l have been associated with chronic disease. A 2012 report of 8,989 adults from the United States National Health and Nutrition Examination Survey (NHANES) 1999–2004 found such levels to be associated with all-cause mortality (1.50, 1.07-2.10), cardiovascular disease (1.69, 1.03-2.77), and heart disease (1.98, 1.11-3.54) after a follow-up of 4.8 years (Tellez-Plaza, 2012 (b)).
To get an idea of cadmium levels in toxicity, a case study of a non-smoking man exposed to cadmium in this occupation as a jeweler had severe osteoporosis and impaired kidney function with a blood cadmium level of 420 µg/l (Chakraborty 2013).
Cadmium and Vegan Diets
Two studies have measured the cadmium levels in vegans.
A 2006 study from the Slovak Republic, of non-smokers, found vegans to have significantly higher blood levels of cadmium than non-vegans (Krajcovicová-Kudládková 2006). However, both groups were relatively low compared to the reference range.
| Table 1. Blood Cadmium Levels | |||
|---|---|---|---|
| Group | µg/l | ||
| Reference: Non-smokersA | 3-12 | ||
| Reference: SmokersA | 6-48 | ||
| Study from Slovak RepublicB | |||
| Non-vegetarians | 0.45 | ||
| Semi-vegetarians | 1.34 | ||
| Lacto-ovo-vegetarians | 1.75 | ||
| Vegans | 3.15 | ||
| A. Chakraborty 2013 B. Krajcovicová-Kudládková 2006 To convert blood cadmium from µg/l to nmol/l, multiply by 8.897. To convert urine cadmium from µg/g creatinine to nmol/mmol creatinine, multiply by 1.006. (Tellez-Plaza 2012 (b)) |
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Six (8%) vegetarians had levels above 5 µg/l and their average duration of vegetarianism was 11 years vs. 6 years in those with levels lower than 5 µg/l. The Slovak Republic appears to have higher cadmium levels than most of the countries in Europe (Harmens 2012).
The researchers didn’t measure for damage from cadmium toxicity and believed that the higher antioxidant status of the vegetarians could protect them from the oxidative damage of cadmium (which may not be the only type of damage).
A 2017 study from Norway found 124 meat-eaters to have similar cadmium levels (1.50 µmol/l) to vegetarians (1.70 µmol/l). The vegetarians included 15 vegans who had similar cadmium levels to the non-vegan vegetarians, though the specific amounts weren’t reported (Fløtre, 2017).
Cadmium and Zinc
In a 2012 article in the scientific journal Medical Hypotheses, Mark McCarty writes about the dangers of cadmium and suggests supplementing with minerals, especially zinc (McCarty 2012), to counter cadmium damage.
For some background, note that the RDA for zinc is 11 mg for men and 8 mg for women, and vegans in EPIC-Oxford had average intakes of 7.9 mg for men and 7.2 for women (not including supplements).
McCarty goes through the research concluding that a high-normal level of cadmium in the blood is linked to vascular disease, diabetes, and cancer. He points out that shellfish and organ meats (liver and kidney) tend to be relatively high in cadmium, but otherwise the chief dietary sources are green leafy vegetables, whole grains, tubers, and root vegetables.
McCarty says that cadmium is absorbed using the same mechanisms for absorbing iron which are up-regulated in iron deficiency and therefore iron deficiency can increase cadmium absorption. I have previously written about how this can also be the case for manganese (see Manganese). Based mostly on animal studies, McCarty argues that the cadmium would also compete with zinc and calcium absorption mechanisms and, therefore, consistent supplementation of both minerals “confer significant protection from cadmium-mediated pathology.”
McCarty makes another argument in favor of zinc supplementation: “It appears that cadmium is innocuous as long as it remains bound to [the mineral-binding protein] metallothionein. This finding is particularly intriguing in light of the fact that cellular expression of metallothionein tends to increase with increased zinc exposure.” Intakes of supplemental zinc in the range of 15–50 mg daily have been shown to boost metallothionein in healthy young men.
McCarty then mentions a number of studies in humans suggesting zinc can be protective:
- A study found that the correlation between serum cadmium and carotid artery thickness was pronounced in subjects with serum zinc in the lower two tertiles but not in the upper tertile.
- A study on urinary cadmium and prostate-specific antigen (PSA) observed a significant correlation in men whose daily zinc intake was below the median level of 12.7 mg.
- A case-control study linked prolonged zinc supplementation with reduced risk for breast cancer in both pre-menopausal and post-menopausal women.
- A clinical trial showed that 45 mg zinc per day exerts a systemic anti-inflammatory effect.
- Supplemental zinc can improve immune function in the elderly.
The only harm from zinc supplementation that McCarty mentions is decreasing copper absorption, something that might not be a concern for vegans. The one reliable study looking at vegan copper intakes, from the USA, found vegans to have an intake of 3.1 mg (men) and 2.2 mg (women) versus 1.3 (men) and 1.5 (women) for non-vegetarians. The RDA for copper is .9 mg for both men and women (Haddad 1999).
One concern about zinc supplementation is whether it could lead to Alzheimer’s Disease. There is some evidence that iron, copper, and zinc are concentrated in the plaques found in the brains of people with AD. Whether copper might be the cause of AD has been of some debate, but there appears to be few if any published studies implicating zinc intakes with AD. See our article on Zinc for more information on zinc and Alzheimer’s Disease.
Zinc Supplements and Cadmium Contamination
In 2001, Krone et al tested six zinc supplements from Seattle area health food stores to see if they contained cadmium (Krone 2001). According to the authors, “Because the chemical properties of [zinc] and cadmium (Cd) are so similar, these two elements invariably occur together in nature.”
They found that the single zinc supplements had very low levels of cadmium whereas the multi-mineral supplements had enough that taking the RDA of zinc would provide up to 2 µg of cadmium (20% of the daily limit recommended by the US Federal Drug Administration (FDA)). It also happens that three of the supplements with low levels of cadmium were in the form of zinc gluconate whereas none of the multi-mineral preparations were the gluconate form. So, it could be that zinc gluconate is unlikely to have much cadmium or that single zinc supplements are unlikely.
According to their website, the supplement manufacturer Kirkman, from Oregon, does a rigorous job testing their supplements for contamination of cadmium and other impurities (more info).