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High-cadmium diet: recipe for stress?

High-cadmium diet: Recipe for stress?

When laboratory rats consume a diet that includes relatively large doses of cadmium, a common metal and environmental pollutant, there is increasing evidence that they become more anxious and unable to deal with stress. The latest such study, conducted by psychologist Jack R. Nation and his colleagues at Texas A&M University in College Station, finds a link between exposure to cadmium and increased alcohol consumption.

Given a choice of drinking water or a 10-percent alcohol solution, rats put on a cadmium-laced diet preferred the liquor, whereas rats munching cadmium-free food favored the water. The former group may have turned to alcohol to ease cadmium-induced anxiety, says Nation. There are other indications of increased anxiety among rats who ingest cadmium, he notes, such as an exaggerated startle response and freezing in their tracks when a loud tone is presented.

But the connection between anxiety and alcohol use is tentative, say the researchers in the September NEUROTOXICOLOGY AND TERATOLOGY, since "there is no consensus in the animal or human literature supporting the tension reduction model of alcohol consumption.'

Adds Nation, "At this point, the data suggest only that research is needed to examine cadmium's effects on humans.'

For 55 days, the researchers fed six rats regular laboratory chow while another six received lab chow containing 100 parts per million cadmium. (Though most humans would not encounter a dose this large, says Nation, similar levels have been seen among people who have had cadmium-poisoning symptoms.) Then, instead of the usual water supply, the researchers gave all the animals a 15-percent alcohol solution for five days in order to familiarize them with alcohol and its effects. Next, a choice between alcohol solution and water was offered for a five-day "baseline period,' then for two weeks during which the animals were trained to press a lever to avoid mild electric footshocks, and finally for nearly three weeks after the footshocks were stopped.

During the stressful shock-avoidance training, cadmium-exposed rats consumed about twice as much alcohol solution as their counterparts and drank slightly more alcohol than water. This pattern became more pronounced in the period following avoidance training, although, says Nation, it is not clear why. There were no significant group differences in total fluid intake, feed intake and body weight.

In a similar study conducted about one year ago, Nation and his colleagues found that rats fed a lead-contaminated diet drank more alcohol than a control group, but the preference for alcohol is considerably stronger when the animals are exposed to cadmium. They have also found that it takes longer for alcohol to affect the behavior of cadmium-exposed rats compared to a control group.

Cadmium is used as a binding agent in the electroplating industry and also in the manufacturing of batteries. Cadmium used by industry is present in sewage sludge, says Nation, which is used by agricultural companies as fertilizer. From there, it enters the food chain. "Cadmium is mobile,' says toxicologist Donald Lisk of Cornell University in Ithaca, N.Y. "It moves readily from soil to plants to animals.'

In the last two years it has been detected in high concentrations in tobacco plants, says Nation. The substance is also known to "load' in some other plants, such as lettuce, says Lisk.

Although its concentrations in human diets vary and have not been fully explored, Lisk adds that "cadmium is at a level that probably should not be exceeded in the American diet.'

Cadmium concentrates in the kidneys, explains Lisk. The first sign of toxicity in humans, he says, is usually kidney dysfunction.
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Author:Bower, Bruce
Publication:Science News
Date:Aug 15, 1987
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