Cadmium is a toxic trace mineral that has many structural similarities to zinc. There is no biological function for this element in humans. Its toxic effects are kept under control in the body by the presence of zinc.
Refining processes disturb the important cadmium-zinc balance. In whole wheat, cadmium is present in proportion to zinc in a ratio of 1 to 120.
Cadmium is found primarily in refined foods such as flour, rice, and white sugar. It is present in the air as an industrial contaminant. In addition, soft water usually contains higher levels of cadmium than does hard water. Soft water, especially if it is acid, leaches cadmium from metal water pipes.
The liver and kidneys are storage areas for both cadmium and zinc. The total body concentration of cadmium increases with age and varies in different areas of the world.
When a deficit of zinc occurs in the diet, the body may make it up by storing cadmium instead. If the daily intake of zinc is high, zinc will be stored and cadmium will be excreted.
Daily intakes of cadmium have been estimated at 0.2 to 0.5 milligram, with considerable variation according to sources and types of food. Cadmium's toxic effects may stem from its being stored for use in the body in place of zinc when the proportion between the two metals is unfavorably out of balance. Zinc is a natural antagonist to cadmium. Cadmium can also interfere with the metabolism of copper.
Dr. Henry A. Schroeder, a trace mineral researcher, has developed a theory about cadmium being a major causative factor in hypertension and related heart ailments. Testing his theories on rats because of their biological similarity to humans, Dr. Schroeder found that regular high doses of cadmium caused increased tension. When he stopped administering the cadmium to the rats, they returned to normotension. In humans, the urine of hypertensive patients contains up to 40 percent more cadmium than does the urine of normotensive persons. These findings may lend credibility to the theory that excessive cadmium can directly lead to hypertension.
Cadmium poisoning is a very subtle process. It deposits in the kidneys, causing kidney damage, and settles into arteries, raising the blood pressure and resulting in atherosclerosis.
Cigarette smoke contains substantial amounts of cadmium. One pack of cigarettes deposits 2 to 4 micrograms into the lungs of a smoker while some of the smoke passes into the air to be inhaled by smokers and nonsmokers alike. The cadmium in cigarette smoke can cause emphysema.