Lead (Pb) and cadmium (Cd) are the most common toxic metals in our environment. Some pollution is natural, some occurs from man’s activities, such as coal and mineral oil burning, smelting, mining, alloy processing, paints, and other industrial processes. Also, Cd exposure is increasing because of increased recycling of electronic equipment.
Pb and Cd are commonly found together and have synergistic* negative effects on health. These are believed to be due to **oxidative stress, and antioxidants are used to treat the effects of those toxic metals. Pb and Cd can damage the central and peripheral nervous systems, blood system, cardiovascular system, kidney, liver and reproductive system.
Cd causes formation of metallothionein (metal binding) proteins and reactive oxygen species (ROS). ROS and free radicals can cause harm to tissues (such as red blood cells), and cellular lipids, protein and DNA. Increased **lipid peroxidation (oxidation of cellular fats) is seen after Cd exposure due to an impaired naturally-occurring antioxidant defense system within cells. Cd acute toxicity damages lung, liver, kidney and testes, while prolonged exposure to Cd damages kidneys, bones, the immune system, and can cause cancer.
Oxidative stress from Pb results in increased ROS, with damage to cell membranes, DNA and proteins. Pb toxicity disables antioxidant enzymes by replacing trace minerals, such as selenium, which are essential for enzyme function. Treatment with selenium prior to Pb exposure reduces the resulting oxidative stress.
There is not clear evidence that antioxidant therapy reduces the effects of Pb and Cd toxicity. Vitamin C (ascorbic acid) is an antioxidant and a possible chelator of Pb, similar to EDTA (ethylenediaminetetraacetic acid). Vitamin C, also, increases the urinary elimination of Pb.
A combination of Vitamin E and Vitamin C may protect lipid structures from peroxidation. Spirulina fusiformis (algae), beta carotene, selenium, and zinc can protect tissues exposed to lead, and zinc might decrease the absorption of Pb in the gastrointestinal tract. (There is a natural competition between the actions of Pb and zinc.) Pretreatment with zinc reduces the toxicity of Cd.
CONCLUSION: Reactive oxygen species (ROS) are produced by cadmium and lead exposure. Oxidative damage results from ROS, causing impairment of enzymes, proteins, DNA and lipid membranes. Some studies show benefits from antioxidant supplementation; however dietary supplementation with antioxidants shows mixed results on studies.
Note: *Synergistic means that two or more “things” are stronger together than they are separately.
**Tissue oxidation is damage to living tissues when they are exposed to oxygen in such things as ROS. It is like the rust of metals when exposed to oxygen and moisture. Lipid peroxidation is the oxidation of fats in living tissues.