Chromium is a mineral that's been gaining some hard-won respect, primarily for its demonstrated ability to normalize blood-sugar concentrations (SN: 5/1/04, p. 282). It can help people exhibiting prediabetic symptoms and those with full-blown type 2 diabetes, the non-insulin-dependent form of the disease.
Because chromium concentrations in most foods are far too low to have much of an effect on blood sugar, health practitioners typically recommend that people augment their diets with mineral supplements. However, two new studies indicate that the quantity of chromium in any supplement may not be nearly as important as the mineral's chemical form.
At the Experimental Biology 2005 meeting in San Diego last week, Robert DiSilvestro and Emily Dy of Ohio State University reported data indicating that only the picolinate form of chromium—one of the four kinds in most commercially available supplements—is absorbed well by the body. About 40 percent of this form was absorbed by people taking chromium supplements in one experiment. In contrast, absorption of other forms of the mineral in supplements ran as low as 1 percent. Only some 10 percent of any form of chromium in foods is typically absorbed, DiSilvestro adds.
Four months ago, Richard A. Anderson of the Agriculture Department's Beltsville (Md.) Human Nutrition Research Center and his colleagues published similar findings in Biological Trace Element Research. However, their experiments included an additional formulation just beginning to make its way onto health-food-store shelves: chromium histidine. That chromium was absorbed almost twice as well as the picolinate was.
Experiments beginning almost a half-century ago showed that giving chromium supplements to diabetic people or other animals could restore blood-sugar control. Questions about the findings included not only why the therapy worked, but what might represent safe, optimum doses of chromium.
Scientists at the Beltsville research center have traced the mineral's action to its control of certain enzymes. Chromium triggers one of these to attach phosphorous-containing molecules to insulin receptors on cells throughout the body. It's a necessary first step before insulin can dock with those receptors.
Only then can insulin shepherd glucose from the blood into energy-hungry cells. When the hormone's job is done, another enzyme comes along and knocks the phosphorous-containing molecule off of the insulin receptors, thereby switching off their activity. It turns out, Anderson says, that chromium inhibits the shutdown enzyme's action too.
Chromium's activity at these receptors would probably be good news for people with diabetes, except that the mineral isn't abundant in today's diets of highly processed foods. Moreover, diets high in sugar stimulate the body to lose chromium, Anderson notes. With all of the refined sugar in today's foods, people probably need more chromium now than they did 50 years ago, he argues, yet they're getting less than they did back then.
Why the different forms?
Supplement manufacturers aim to make products that are nontoxic, easy to manufacture uniformly, and chemically stable for a long shelf life. They also want ingredients that will easily fit into tablets.
That last concern drove makers of multivitamin-and-mineral tablets to favor chromium chloride, owing to that molecule's small size, DiSilvestro observes. "People don't want to take 10 pills a day or one big horse pill that's going to choke them," he quips.
The problem, DiSilvestro says, is that his new data indicate that human absorption of chromium chloride was the worst of the four tested formulations. When the dozen women in the new study took 200 micrograms of chromium as chromium chloride, they ended up with only 30 percent more chromium in their bodies than what they had obtained from their diets alone.
Chromium nicotinate, known as GTF, for glucose-tolerance factor, has become commercially popular in the past few years. In this study, women absorbed two times as much of this formulation as from their diet alone.
Preliminary reports by other researchers had suggested that this chromium form is absorbed better than other forms and the form that the body relies on to moderate blood sugar. DiSilvestro says, however, that those findings were artifacts of the way the bloodborne chromium was measured. Indeed, he says, the idea that the GTF nicotinate "was the glucose tolerance factor may be a figment of our imaginations."
The Ohio State scientists' analysis of another supplement, chromium nicotinate with some extra attached amino acids, was absorbed better than the GTF form. It yielded about three times as much chromium to the women's tissues than what their diets had provided.
The best performer by far was the chromium picolinate, which is chromium bound to picolinic acid. The Ohio State researchers found that the supplemental chromium in this form gave the women about six times as much of the mineral as they received from their diet.
This study was financed by Nutrition21, a company that makes dietary supplements, including chromium picolinate under the trade name Chromax.
An even better form
USDA scientists have been studying chromium absorption and function in human health for 3 decades, during which time they patented chromium picolinate. Anderson's team has recently done that formulation one better, by coupling chromium with the essential amino acid histidine.
In February, Anderson's group received a patent for this combination after establishing that it's absorption by the body is much better than that of plain chromium picolinate. New work by the researchers has also established that the new chemistry makes chromium a more potent antioxidant than it is in any of its other forms.
So far, no company has licensed the histidine formulation for a commercial supplement. That hasn't stopped some firms from marketing it anyway, Anderson observes.
In a paper published last December, his team compared chromium histidine's absorption to that of nine other chromium formulations in three men and three women. The formulations included the four studied by DiSilvestro. In this federally financed study, the unchallenged top performer was the chromium histidine. Its absorption was more than 50 percent better than that of chromium picolinate.
The current recommended minimum daily intake of chromium for most adults ranges from 20 to 35 µg, depending on a person's size and age. A woman breastfeeding a child should get at least 45 µg per day. For children 1 to 8 years old, the recommended minimum intake is 11 to 15 µg.
A person could get such amounts of the mineral from food, without the need for a supplement. A cup of cooked broccoli, for instance, typically contains 22 µg of chromium, and 3 ounces of cooked turkey-leg meat has 100 µg.
What's driven the interest in chromium supplements has been a growing host of studies showing the mineral's effect in people prone to or with diabetes. However, far higher doses of chromium than what are in typical supplements might be needed to achieve this benefit. For instance, Anderson's lab is currently testing the effects of about 1,000 µg of chromium per day in people with type 2 diabetes.
Richard A. Anderson
Beltsville Human Nutrition Research Center
Building 307C, NRFL
Beltsville, MD 20705
Department of Human Nutrition
Ohio State University
345 Campbell Hall
1787 Neil Avenue
Columbus, OH 43210-1295
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