A study by the Department of Agriculture about the trace mineral chromium in the diet (Eating Right, May 29), was on high blood sugar -- hyperglycemia -- not hypoglycemia, as reported. (Published 6/ 12/90)
First there were vitamins. Then came calcium supplements. Now one of the hottest areas of nutritional interest is trace minerals.
Trace minerals -- also known as trace metals -- run the gamut from copper to zinc. Some are well-known, such as iodine, which is essential for proper thyroid function, and iron, which prevents anemia. Others are more obscure. They include chromium, which is crucial in maintaining blood sugar levels; manganese, which helps strengthen bones, and selenium, which has been shown to be important for cardiac function and as a protection against cancer.
New research suggests that these substances, which abound in various foods, are not merely important on their own but in the way they interact with each other and with other essential nutrients, including vitamins.
"There's a realization that diets need to be considered in their entirety, rather than just single nutrients," said Richard S. Rivlin, a physician who heads the nutrition division at the New York Hospital-Cornell Medical Center. Several studies, for example, show that too much zinc interferes with copper metabolism. Copper helps maintain red blood cells, among other functions.
People who are healthy and eat a balanced diet probably need not worry about getting adequate amounts of trace minerals, according to Yvonne Bronner, a spokeswoman for the American Dietetic Association.
The problem is that many Americans -- such as those who are on low calorie or other diets and the elderly, who tend to have poor eating habits -- often don't eat well-balanced meals. In addition, trace minerals are particularly important for proper development in children and women who are pregnant or breast-feeding.
Deficiencies in trace minerals can lead to health problems. A study presented last month at the annual meeting of the Federation of American Societies for Experimental Biology found that elderly women suffering from the gradual loss of bone mass known as osteoporosis had blood levels of manganese one third lower than a group of healthy women of the same age. Analysis of their diets showed that women with osteoporosis, who are prone to disabling hip fractures, consumed 25 percent less manganese than the healthy women. Yet absorption studies showed that they had "a far greater need for the mineral," reported Jeanne Freeland-Graves, co-author of the study and a professor of nutrition at the University of Texas at Austin. Rich sources of manganese include unrefined cereals, green leafy vegetables and tea.
U.S. Department of Agriculture researchers found that a diet deficient in chromium can exacerbate hypoglycemia, the low-blood-sugar condition that causes faintness, hunger and heart palpitations and often precedes the development of adult-onset diabetes. Hypoglycemia -- also known as glucose intolerance -- develops in adults when the pancreas secretes less efficient insulin, the hormone responsible for moving sugar from the blood into cells.
In a 14-week study of 17 people, USDA researchers found that adding 200 micrograms a day of chromium helped return blood sugar levels to normal in eight people with hypoglycemia. After five weeks, blood sugar levels in the hypoglycemic group rose to an average of 170 mg.
Finnish researchers report that diets low in selenium, found in seafood, liver and meat, increase the risk of developing cancer. Researchers drew blood from nearly 40,000 people who were participating in a health examination survey. They measured blood levels of selenium and then tracked the participants for 10 years.
"Low serum selenium levels were associated with an increased risk of developing cancer at several sites, especially . . . the stomach and lung among men," the researchers wrote in the Journal of the National Cancer Institute.
Taking trace mineral supplements usually is not the solution, experts say. "You shouldn't take large amounts of trace minerals without really knowing what you are doing and without taking them in balanced fashion, under the supervision of a qualified health professional," said Rivlin.
While deficiencies of trace minerals can cause health problems, so can high levels, which can have toxic effects ranging from vomiting and diarrhea to neurological symptoms resembling Parkinson's disease.
Popping a daily multi-vitamin also won't necessarily assure the minimum requirements either, since many tablets don't contain trace minerals. The best bet, experts say, is simply to follow a balanced diet.
Eating Right appears on alternate Tuesdays.