How does cadmium elevate blood lead levels

How can a toxic effect of cadmium cause a small elevation of blood or hair lead above the average for that environment?

To understand the behavior of metals it is necessary to look at their biochemical behavior.   Statistical correlations can be misleading. It has been known for a long time that zinc and iron deficiencies were associated with toxic effects of lead.  These deficiencies are known to increase the absorption and toxicity of cadmium.   The inhibition of the enzyme ALAD which is considered particularly characteristic of toxicity to lead occurs with cadmium.   Zinc protects this enzyme from inhibition. Cadmium is an anti-metabolite of zinc. Zinc protects cells from cadmium toxicity. So lead toxicity is not just a simple matter of exposure to a toxic metal and a toxic effect that one can measure with blood lead levels or inhibition of ALAD. 

 An excellent article is available regarding the use of dietary strategies for the treatment of lead and cadmium toxicity.

Nutrients. 2015 Jan 14;7(1):552-71. doi: 10.3390/nu7010552.

Dietary strategies for the treatment of cadmium and lead toxicity.

Zhai Q¹, Narbad A², Chen W³.

In this article the effects of vitamins, minerals, herbs, and probiotics on toxic effects of lead and cadmium are discussed. In most cases it is clear that a reduction of blood lead with these strategies also reversed toxic effects of cadmium. 

 One could consider that both lead and cadmium are toxic but that elevation of blood lead is the indicator of toxicity, not blood cadmium.  Certainly the toxicity is directly associated with deficiencies of vitamins and minerals. However, one could also consider that lead exposure directly influences the uptake of cadmium.

 Cadmium is very interactive with all nutrient and toxic metals and also with toxic chemicals. Lead is treated more like calcium in the body and is stored in bone. Cadmium is stored in the lining of blood vessels and in the choroid plexus surrounding the brain. It is in the kidney, liver, ovary, testes, thyroid, and adrenals. With acute stress, like handling an animal, cadmium is released into the body.  Consequently, cadmium effects can occur without directly adding cadmium to an experimental animal.   

Cadmium causes a stress response in all cells. Lead does so only through increasing the absorption of cadmium.  For instance, lead in water increases metallothionein production in the liver.  Metallothionein is part of the acute stress response that cadmium produces.  Cadmium activates the promotor of metallothionein  whether cadmium has been added in the experiment or not. When lead is directly added to liver cells there is no increase in metallothionein production. Lead in drinking water increases the uptake of cadmium which promotes the stress response resulting in increased metallothionein production. It is not just that lead and cadmium are both toxic.  Toxic effects attributed to lead are caused by cadmium.

It is this effect of lead ingestion increasing the absorption of cadmium that is directly related to the small but significant elevations in blood lead levels and health effects.  Cadmium increases resorption of bone where lead is stored increasing blood lead levels.  So the level of lead in blood is not a measure just of exposure,but exposure plus a toxic effect of cadmium on bone. Blood cadmium is not a helpful measurement because cadmium is taken up rapidly into the blood vessels and the various organs.  The levels are highly variable through the day responding to various stresses.  Blood hair, and urine cadmium levels are not just measures of exposure but also of stressed induced releases.  

 Based on this information alone, it is clear that cadmium is important. It should be measured accurately in air. New approaches are needed to detect these volatile ultrafine fumes of cadmium.  The US EPA needs to fund research on effective ways to measure cadmium.   Children with elevated blood lead levels should be evaluated for toxic effects of cadmium.  Their urine cotinine should be measured to determine exposure to environmental tobacco smoke.  Children in tee highest quartile of urine cadmium have a three fold risk for placement in special education. These children need the dietary strategies suggested by Q Zhai et al.  They need stress reduction and excellent care both at home and at school. They are not permanently damaged.  It is neglect and indifference that leads to permanent damage in most instances.