ADA 2008: Be wary of trace element claims

Clinicians should be wary of health claims made for trace elements such as iron or chromium. While there is no doubt that trace elements are needed for health, there is significant doubt about their utility in preventing or curing diabetes and other diseases, said Eliseo Guallar, MD, DrPH, Johns Hopkins Bloomberg School of Public Health, Baltimore. There are many hypotheses about the beneficial effects of trace elements, but little high-quality data, little reliable population data, few useful biomarkers, relatively crude analytical methods and few mechanistic studies.

"Large randomized controlled trials would be very helpful in evaluating trace elements," Dr. Guallar explained. In some cases, confusion is understandable. Iron, for example, clearly contributes to diabetes in patients with hemochromatosis, a largely hereditary condition that results in a pathologic increase in iron stores. The role that iron plays in normal patients is less clear.

"Iron overload causes diabetes. That is clear," he said. "The question is the effect of smaller elevations."

Multiple studies have found elevated levels of serum ferritin, the primary human iron storage protein, associated with multiple disorders, including diabetes and cardiovascular disease. Researchers have suggested that excessive iron levels may contribute to diabetes by three pathways.

One pathway suppresses hepatic function. Another induces insulin resistance. A third pathway increases oxidative stress on beta cells, leading to beta-cell apoptosis and declining levels of insulin production.

Researchers have also found associations between elevated serum ferritin and an elevated risk of diabetes. But whether ferritin elevation preceded diabetes or proceeded from the disease is not clear, Dr. Guallar said. Elevated ferritin levels may also reflect the general effect of widespread inflammation, which is known to increase iron stores.

Evidence that chromium may prevent diabetes is even more tenuous, he said. Chromium supplements are widely advertised and marketed to increase lean body mass and prevent diabetes, among other purported benefits, Dr. Guallar noted. Supermarkets, drug stores, and health food store shelves are crowded with competing chromium supplements.

"There is a lot of commercial interest in promoting chromium supplements," he said. "There is less evidence that they are effective."

Chromium has been studied at least since the 1970s, he said. And while OTC chromium marketers trumpet studies supporting their products, the data are inconclusive at best.

Chromium is widely available in most diets, Dr. Guallar pointed out. It occurs in processed meats, whole grain products, vegetables such as green beans and broccoli, even in some types of beer and wine. Sucrose and glucose are low in chromium and enhance elimination of the mineral, but most diets appear to provide adequate amounts.

Studies have shown that increased chromium intake has no effect on lean body mass or on weight loss, two of the most common claims made for the mineral.

"It is clear that chromium has no effect on glucose metabolism and likely no effect on diabetes," he added.