Researchers Update Micronutrient RDAs

WASHINGTON--On Jan. 9, a 561-page report suggesting Recommended Dietary Allowances (RDAs) and Tolerable Upper Intake Levels (ULs) for 12 micronutrients hit the news waves. These findings came from a research panel at the National Academy of Sciences' Institute of Medicine's Food & Nutrition Board (FNB), and media outlets including CNN.com, MSNBC.com and the Associated Press (AP) took part in spreading the word.

The most newsworthy part of the report included establishing a UL for vitamin A: 3,000 mcg/d (or 10,000 IU) for adults and an RDA of 900 mcg/d for men and 700 mcg/d for women. While a lack of vitamin A may cause blindness, excess vitamin A intake may increase the risk of birth defects, liver problems for adults. Most Americans achieve 70 percent of this RDA from consumption of meat, milk, fish, green leafy vegetables and deep orange or yellow fruits and vegetables.

In addition, the report questioned the "B-Carotene factor." The factor relates to how much beta carotene constitutes one unit of vitamin A. According to Robert Russell, a professor of medicine and nutrition at Tufts University School of Nutrition and chair of the FNB panel, it was reported in 1989 that six units of dietary beta carotene equaled one unit of absorbable vitamin A. However, Russell stated the correct amount is 12 units.

Also, the report noted that almost half of all pregnant women might be iron deficient, which may lead to premature delivery, spontaneous abortion and birth defects. The RDA for iron was set at 27 mg/d for pregnant women, as well as 8 mg/d for men and 18 mg/d for premenopausal women. A UL intake was set at 45 mg/d; according to the report, some research has suggested that elevated iron stores may lead to a higher risk for heart attacks and cancer.

RDAs were also set for vitamin K (90 to 120 mcg/d), chromium (25 to 35 mcg/d), copper (900 mcg/d), iodine (150 mcg/d), molybdenum (45 mcg/d) and zinc (8 to 11 mg/d). A UL was set for boron (20 mg/d), copper (10,000 mcg/d), iodine (40 mg/d), molybdenum (2,000 mcg/d), nickel (1.1 mg/d), vanadium (1.8 mg/d) and zinc (1,100 mcg/d). Rather than an RDA, the panel set an adequate intake (AI) level for manganese of 1.8 to 2.3 mg/d with a UL of 11 mg/d. Neither an RDA nor a UL were set for arsenic or silicon; at the panel's press conference, Russell stated that the available data and reported responses were not as extensive as those for the other micronutrients.

This is the fourth report in a continuing line of research about updating RDAs, and it follows the April 11, 2000, report on vitamins C, E and selenium. The FNB's panel on micronutrients based intake levels on scientific literature from the United States and Canada, such as the Third National Health & Nutrition Examination Survey (NHANES III) that followed 33,994 people from 1988 to 1994.

The Council for Responsible Nutrition (CRN) found FNB's report to be consistent with CRN's 1997 document Vitamin and Mineral Safety. However, minor differences were found between FNB's ULs and CRN's. "One point of concern is the low recommendations for chromium that are based on the usual intakes in apparently healthy people, rather than the clinical trial data from people with impaired glucose tolerance," said John Hathcock, vice president of nutritional and regulatory science at CRN.

The FNB researchers concluded that more studies needed to be conducted to understand the functional and biochemical endpoints of sufficient and insufficient levels of nutrients, as well as the interactions between micronutrients.

For more information about the FNB report, visit www.iom.edu; for a copy of the NHANES III survey, visit www.cdc.gov/nchs; and for more about CRN, visit www.crnusa.org.