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Heavy Metal Toxicity and Cancer

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Posted on 10-31-2017

Heavy Metals have now become a fabric of our environment. They are found every where- from our drinking water, in the workplace, in the air and in our food. While some heavy metals do have a physiological role in the body like zinc and magnesium, most other heavy metals are just plain toxic like mercury, lead, and arsenic. There have been many reports of toxicity of heavy metals lately. Further, the latest scientific evidence indicates that many of the metals are also potent carcinogens. Some of the cancers caused by these heavy metals include breast cancer, lung, bladder, prostate, skin, and even brain.

Over the past few decades, the rates of many cancers have sharply increased and it is now believed that perhaps that environmental factors may be playing a role. Besides the usual risk factors like smoking, alcohol, and obesity, there is good evidence to indicate that heavy metals may be initiating or promoting carcinogenesis.  Several epidemiological studies have shown an association between cancer and exposure to metals like zinc, arsenic, cadmium, nickel, and even lead; all these metals exist naturally in the environment. It is believed that once the metals are ingested they may mimic the actions of hormones or stimulate cancer oncogenes.

Here we provide you with a brief synopsis of the heavy metals and associated cancers.

1. Arsenic is widely spread into the environment and has been linked to several different types of cancers. Today both inorganic and organic arsenic compounds are used as herbicides, insecticides, and even wood preservatives. Recent epidemiological studies reveal that arsenic in drinking water may be associated with cancers of the bladder, skin, lung, and kidney in humans. These cancers appear to occur after prolonged exposure to arsenic compounds. Also of concern is the use of arsenic trioxide, which is found in several traditional Chinese medicines. This compound has been used for the treatment of some hematological cancers but its antitumor effects have not been seen with other cancers. Arsenic trioxide is known to induce apoptosis in cancer cells but the final triggers signaling apoptosis are not known. Other laboratory evidence reveals that arsenic at low concentrations can induce proliferation of breast cancer cells, while at high doses may induce apoptosis. However, most studies on arsenite in concentrations found in the environment suggest that it can induce replication and induce breakage in the double strands of DNA. Further, other studies show that low dose arsenic can also induce the generation of reactive oxygen species and lead to oxidative stress.

2. Cadmium is not a required metal for humans and has been categorized as a human carcinogen by the EPA. The primary source of cadmium is from tobacco and food. Cadmium has been linked to many cancers including breast and prostate. Several studies indicate that people with high levels of cadmium may be at risk for breast cancer; how it causes cancer is not known but could be due to cell proliferation, apoptosis, or differentiation. Cadmium has been shown to function like an endocrine hormone disruptor. It stimulates estrogen receptors and promotes the growth of mammary and uterine issues in animals; it has also been shown to diminish the protective effects of selenium in mice carrying the breast cancer murine virus. Interestingly melatonin has been shown to prevent cadmium-induced cancer in the laboratory and it is now being studied in more details to determine if it has a role in human breast cancer prevention.

3. Lead. With the rising rates of breast cancer in the industrialized world, there are some experts who believe that perhaps the environment may have something to do with it. Today the role of lead and its role in causing breast cancer is being studied. Lead is widely spread in the air, water, and soil and is also released from industrial plants. For many years, there has been concern about lead in the environment. Laboratory data shows that even low levels of lead can accelerate tumor growth. Plus, women who have been diagnosed with several subtypes of breast cancer have been found to have high levels of lead in the hair and blood. The toxicity of lead is due to increased generation of reactive oxygen species and interference with the generation of antioxidants. Lead is known to cause generation of hydrogen peroxide, hydroperoxide, and singlet oxygen species. These changes result in lipid peroxidation and damage to cells and the nuclei. Since only a few studies have been published, the overall evidence for lead as a carcinogen is currently being weak, the most likely prolonged exposure can lead to stomach cancer, lung cancer, and gliomas.

4. Nickel is found naturally occurring in the environment and found in food and water. Much of the nickel found in urban areas is due to human pollution from industrial waste. Humans may also acquire nickel from smoking and through contact with jewelry, detergents, and coins. While the average daily exposure of nickel does not pose a threat, there is more evidence indicating that long-term exposure to nickel may lead to cancer. ADD

OSHA has sets limits for nickel in the workplace but outside the workplace nickel level is often unregulated. Studies show that nickel can induce various cancers in animals by activating hypoxia-inducible factor and altering gene expression of several growth factors.

Conclusion

There are many anecdotal reports of cancer caused by heavy metals but unfortunately, we do not have long-term studies. The difficulty with studying cancer is that the malignancy does not happen immediately and often takes years to present. Over time, other confounding factors may appear and the individuals often get lost to follow-up. Irrespective of the lack of evidence and what the governmental agencies claim, there is little physiological role for most heavy metals in the human body. In the meantime, the public is best advised to minimize exposure to all heavy metals. The bottom line is that there is no safe level for most of these metals.

References

Tan SY, Praveena SM, Abidin EZ, Cheema MS. A review of heavy metals in indoor dust and its human health-risk implications. Rev Environ Health. 2016 Dec 1;31(4):447-456.

Núñez O, Fernández-Navarro P, Martín-Méndez I, Bel-Lan A, Locutura Rupérez JF, López-Abente G. Association between heavy metal and metalloid levels in topsoil and cancer mortality in Spain. Environ Sci Pollut Res Int. 2017 Jan 20.

Romanjuk A, Lyndin M, Moskalenko R, Gortinskaya O, Lyndina Y The Role of Heavy Metal Salts in Pathological Biomineralization of Breast Cancer Tissue. Adv Clin Exp Med. 2016 Sep-Oct;25(5):907-910.

Park SS, Skaar DA, Jirtle RL, Hoyo C. Epigenetics, obesity and early-life cadmium or lead exposure. Epigenomics. 2017 Jan;9(1):57-75.

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