Circulation: Cadmium & Blood Pressure

“I may be wrong,” the distinguished physiologist admitted to the American Heart Association meeting in Manhattan. But if he was right, Dr. Henry A. Schroeder had not only provided an explanation for millions of hitherto inexplicable cases of high blood pressure; he had also suggested a possible method of treatment. Dr. Schroeder had also pointed out a mechanism by which diabetes may develop in adult Americans, and he had outlined an approach to prevention of the disease.

If an investigator of less repute had reported such heady stuff, the audience of hypercritical physicians would surely have scoffed. Indeed, many of them smiled tolerantly when Dr. Schroeder first drew attention to a puzzling association between the softness of the drinking water in an area and the frequency of hardened arteries among men who live there (TIME, May 2, 1960). However, the determined physiologist had already taken to the hills and found both an explanation and supporting evidence for his observations.

Sunken Nails. From the start, Dr. Schroeder did not believe that the growing incidence of arterial disease reflected the presence of such common and natural drinking-water constituents as calcium bicarbonate, with which man has lived throughout history. What concerned the imaginative researcher was pollution by metals that modern man, the metallurgist, now scatters around him in profusion.

What was needed was a laboratory free from metallic contamination. Dr.

Schroeder constructed one high on a 1,600-ft. Vermont hill near his home base at Dartmouth Medical School.

The building was all wood, with the nails sunk and sealed in. Anything that might contain lead or cadmium was excluded; the principal exception to the no-metal rule was stainless steel for the cages that contained experimental rats and mice. Water pipes, where possible, were made of plastic. The pure mountain air was electrostatically filtered. Visitors were barred because they might carry metalliferous dust; even research-staff members had to take their shoes off before entering the animal rooms. The animals were fed a diet with a meticulously defined metallic content, and their pure drinking water was superpurified. Whether it was hard or soft depended on how the investigators treated it.

Kidney Analyses. Among the 20 elements that Dr. Schroeder investigated as potential artificial pollutants, cadmium produced the most striking results. Rats given minute traces of cadmium salts in drinking water all their lives developed high blood pressure of a type remarkably similar to the human disease. More females than males developed the disease, but it was deadlier to the males; the animals developed fatty plaques in their aortas, and showed enlargement of the heart. When rats receiving cadmium were divided into two groups, 80% of those on soft water developed high blood pressure as against only 17% of those on hard (calcium-containing) water. When the animals were treated with a drug that substituted zinc for the cadmium already in their tissues, blood pressures returned to normal.

The next question was obvious: Do humans react like rats when they ingest cadmium and other metals? By way of answer, Dr. Schroeder offered chemical analyses of 400 human kidneys showing that Americans at birth have a negligible amount of cadmium stored there, that the amount of the metal increases gradually with age and reaches its highest levels in patients with high blood pressure of unknown origin. He did not have to remind his medical audience that kidney function is important in regulating blood pressure, and that many cases of high blood pressure are clearly associated with kidney disorders.

Civilized man, said Dr. Schroeder, ingests an excess of cadmium from tea and coffee, refined flour and polished rice, some phosphate-fertilized crops— and water pipes. Soft water, he declared, takes up cadmium, a contaminant in copper and galvanized pipes, far more readily than does hard water.

Chromium Decline. Another of the 20 elements studied was chromium. All over the world, people are born with relatively generous amounts of chromium in their vital organs, but in the U.S. the levels decline precipitously around age ten. By juggling his rats’ intake of chromium, Dr. Schroeder found that a severe shortage, such as afflicts many adult Americans, caused many of the rats to develop first diabetes and then artery disease—a condition remarkably like progressive human diabetes. With animals kept at what Dr. Schroeder considers a normal chromium level, there was virtually no diabetes or atherosclerosis. “Specialists in diabetes and in atherosclerosis,” he said, “are beginning to see their disciplines overlap.”

Cautiously, Dr. Schroeder pointed out that he was not simplistically laying all the blame for high blood pressure and atherosclerosis on cadmium and chromium. Other exotic elements such as vanadium, zirconium and niobium, all “abundant in the human body,” influence the level of fats in the blood.

And these, said Dr. Schroeder, are metals to which newly exposed man has little or no ability to adapt.