Don’t Go Overboard With Dietary Supplements

By:
Tom Nordlie (352) 392-1773 x 277

Source(s):
Bob Cousins, rjc@gnv.ifas.ufl.edu, (352) 392-2133

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GAINESVILLE, FL—Health conscious? Don’t overdo the nutritional supplements, advises a University of Florida nutritional biochemist.

“Some people may use excessive amounts of nutrients for weight loss, athletic performance or health maintenance, without considering possible adverse effects,” said Bob Cousins, who helped formulate new recommendations on nutrients for the National Academies’ Institute of Medicine in Washington, D.C.

The recommendations are part of a report on Dietary Reference Intakes released by the academies earlier this month.

Cousins served on a panel of experts that examined the nutritional value of vitamins A and K, arsenic, boron, chromium, copper, iodine, iron, manganese, molybdenum, nickel, silicon, vanadium and zinc.

Besides updating the well-known Recommended Dietary Allowances, or RDAs, the panel estimated — for the first time — nutrient intake levels “that are likely to pose no risk of adverse health effects.” These levels serve as recommended maximums for daily intake, and are called “tolerable upper intake levels.” The report says these levels are not likely to be obtained from ordinary foods, Cousins said.

“These new recommended maximums are a sign of the times,” said Cousins, professor and eminent scholar with UF’s Institute of Food and Agricultural Sciences. “Many of the nutrients reviewed in our study are being consumed in amounts that would be impossible to achieve through diet alone.”

Iron supplements have long been used to prevent anemia, particularly among pregnant women, he said. The panel’s new recommended intake for pregnant women — 27 milligrams per day — is about half the tolerable upper intake level recommended for healthy adults — 45 milligrams per day.

“Excessive iron intake can cause gastrointestinal distress,” Cousins said. “It also may be linked to heart disease and cancer in people genetically predisposed to accumulate high levels of iron.”

Zinc, popular in cold remedies, has a new recommended maximum intake of 40 milligrams per day. But the average zinc cold lozenge contains more than 20 milligrams of the mineral, Cousins said. Excessive zinc intake can lead to copper deficiency and cause anemia, and may cause immune system disfunction.

“A few zinc lozenges combined with zinc intake from foods like red meat can put your daily intake way over the tolerable upper intake level,” said Cousins, an international expert on zinc. “In the short term, our bodies can cope with high levels of many nutrients, but the long-term effects are unknown.”

Cousins, who directs UF’s Center for Nutritional Sciences, said nutrient toxicity has not been closely studied, and ethical considerations limit research on human subjects.

“As a result, many nutritional supplements have never been tested in well-controlled trials,” he said.

One example is chromium, used in diet aids such as chromium picolinate. Chromium’s role in human nutrition is unclear, so the panel did not establish a recommended intake for the metal, he said.

“Chromium is believed to play some role in glucose regulation,” Cousins said. “But long-term effects of chromium supplementation have not been widely studied.”

Substantial amounts of chromium and other nutrients are routinely added to “meal replacement” drinks and candy bars marketed to dieters and athletes, he said.

“More and more products are fortified with nutrients today, but you probably don’t want to carry a pocket calculator to the dinner table to keep track,” Cousins said. “If you eat a balanced diet of foods from each of the food groups and watch your supplement use, you should be fine.”

Cousins, elected as a member of the National Academy of Sciences in May 2000, said the public is becoming more aware of nutrition-related issues. He believes the report will influence advertising, food labeling and government policy decisions. The report is the fourth in a series of seven, developed by the United States and Canada to review nutritional data.

Other recommendations in the report include:

  • Vitamin A — Essential to vision and reproduction, vitamin A is produced from carotenes found in carrots, sweet potatoes, broccoli, meat and eggs. Recommended daily intake is 900 micrograms for men, 700 for women. The report says that to achieve these intakes, more vegetables and fruits must be consumed than was previously believed. Tolerable upper intake level is 3 milligrams per day; excessive intake may increase the risk of birth defects, skull malformations in children and liver abnormalities in adults.
  • Vitamin K — Necessary for blood clotting, vitamin K is found in leafy green vegetables. Adequate daily intake is 120 micrograms for men, 90 for women. No tolerable upper intake level was established.
  • Copper — Used for development of connective tissue, nerve coverings and skin pigment, copper is found in organ meats, seafood, nuts and seeds. Recommended daily intake is 900 micrograms for both men and women. This is the first time a recommended intake for copper was established. Tolerable upper intake level is 10 milligrams per day; excessive intake may cause liver damage.
  • Iodine — An important component of thyroid hormones, iodine occurs in small amounts in seafood and is often added to table salt. Recommended daily intake is 150 micrograms for men and women. Tolerable upper intake level is 1.1 milligrams per day; excessive intake can cause abnormal functioning of the thyroid gland in some individuals.
  • Manganese — Involved in metabolism and bone formation, manganese is found in nuts, legumes, whole grains and tea. Adequate daily intake is 2.3 milligrams for men, 1.8 for women. Tolerable upper intake level is 11 milligrams per day for adults; excessive intake may cause neurological side effects.
  • Molybdenum — Used for enzyme enhancement, molybdenum is found in nuts, legumes and grain products. Recommended daily intake is 45 micrograms for men and women. Tolerable upper intake level is 2 milligrams per day; excessive intake may cause impaired reproduction and growth.

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Posted: January 23, 2001


Category: UF/IFAS



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