Cadmium (Cd)
Killer of immunity or growth stimulator?
Cadmium belongs to toxic (immunotoxic) ultratrace elements, being one of the main environmental pollutants. Its negative effect on the human body manifests even at very low concentrations (3–300 µg per day). At doses of 1–9 g, cases with fatal outcomes are possible. However, at the same time, cadmium belongs to the group of “new” trace and ultratrace elements (cadmium, vanadium, tin, fluorine) and can stimulate the growth of certain animals at low concentrations.
The daily requirement of the human body – 1–5 µg. A deficiency of cadmium in the body can develop with insufficient intake of this element (0.5 µg/day or less).
An adult human receives 10–20 µg of cadmium per day. Less than 5% of the cadmium ingested with food is absorbed in the small intestine. The absorption of cadmium is significantly influenced by the presence of other bioelements and food substances, such as calcium, zinc, copper, dietary fibers, etc. Cadmium inhaled from the air is absorbed significantly better (10–50%).
In the human body, cadmium accumulates mainly in the kidneys, liver, and duodenum. With age, the cadmium content in the body increases, especially in men. The average concentration of cadmium in men and women is 44 and 29 µg/g in the kidneys, 4.2 and 3.4 µg/g in the liver, and 0.4–0.5 µg/g in the ribs, respectively.
Cadmium is primarily excreted from the body through the intestines. The average daily excretion rate of this element is very low, amounting to no more than 0.01% of the total amount of cadmium in the body, according to some data. Estrogens enhance the excretion of cadmium, which may be related to the activation of copper metabolism.
The metabolism of cadmium in the body is characterized by the following main features: the absence of an effective mechanism for homeostatic control; prolonged retention (accumulation) in the body with a very long half-life (on average – 25 years); predominant accumulation in the liver and kidneys; intense interaction with other divalent metals both during absorption and at the tissue level.
Biological role in the human body. The physiological role of cadmium is not well studied. It is believed that cadmium affects carbohydrate metabolism, activates a number of enzymes, plays a role in the synthesis of hippuric acid in the liver, participates in the metabolism of zinc, copper, iron, and calcium in the body. Cadmium is also found in the composition of the so-called metallothionein – a protein characterized by a high content of sulfhydryl groups and heavy metals. The function of metallothionein is to bind and transport heavy metals and their detoxification. In vitro, cadmium activates several zinc-dependent enzymes: tryptophan-oxygenase, DALA-dehydratase (delta-aminolevulinic acid dehydratase), carboxypeptidase. However, no enzymes activated exclusively by cadmium have been found.
The main problems humanity faces with cadmium are due to technogenic pollution of the environment, and its toxicity to living organisms even at low concentrations.
Synergists and antagonists of cadmium.
Sulfur,
selenium,
zinc,
copper,
calcium, and dietary fibers slow down the absorption of cadmium. Zinc and copper can displace cadmium from the body.
Signs of cadmium deficiency: experimental deficiency of cadmium in laboratory animals is associated with slowed growth.
Cadmium belongs to immunotoxic elements. Many cadmium compounds are toxic.
With excessive intake of cadmium into the body, especially prolonged exposure, chronic cadmium poisoning develops, primarily affecting the urinary and reproductive systems. Proteinuria, glucosuria, aminoaciduria, β2-microglobulinuria, the appearance of protein binding retinol and lysozyme in urine, prostatopathy with a risk of neoplasms and testicular necrosis are observed. Damage to the bronchopulmonary system is accompanied by fibrotic changes and an increased risk of developing emphysema. Anemia develops, associated with reduced iron absorption in the intestine and with hemolysis of erythrocytes. Blood pressure increases. Osteoplastic and osteoporotic changes in bone tissue are noted, which are related to impaired calcium absorption in the intestine and endocrine disorders (in other words, cadmium “leaches” calcium from the bones).
Smoking just one cigarette increases the intake of cadmium into the body by 0.1 µg (i.e., significantly increases the risk of cadmium intoxication). The role of cadmium in the induction of lung cancer and kidney cancer in smokers is proven, as well as the development of prostate pathology.
The placenta protects the fetus from the toxic effects of cadmium during pregnancy, and breast milk protects the newborn.
Causes of excess cadmium: excessive intake (e.g., from tobacco smoke, during occupational exposure), deficiency of zinc, selenium, copper, calcium, iron.
Main manifestations of cadmium excess: prostatopathy; cardiopathy, hypertension; pulmonary emphysema, osteoporosis, skeletal deformity (duck walk); nephropathy; anemia; development of deficiencies in zinc, selenium, copper, iron, calcium.
Cadmium is necessary: in disorders of growth processes.