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.