Dietary Reference Intakes for Vitamin A, K, and minerals

[Kuester, Sarah]

Hello.  Below is the press release from the Institute of
Medicine regarding their latest report "Dietary Reference 
Intakes for Vitamin A, Vitamin K, Arsenic, Boron, Chromium, 
Copper, Iodine, Iron, Manganese, Molybdenum, Nickel, Silicon, 
Vanadium, and Zinc."  Please see the end of the press release
for information how and when to obtain the final report.  You can
view a prepublication copy of the report at the National Academy
Press website at http://books.nap.edu/catalog/10026.html (or go 
to http://www.nap.edu/ and search for the report by title).

Thank you,
Sarah Kuester
Public Health Nutritionist
Centers for Disease Control and Prevention
sak2 at cdc.gov 
------------------------------------------------------------------------
Source: http://national-academies.org/
National Academies, Institute of Medicine
Date: Jan. 9, 2001
Contacts: Bill Kearney, Media Relations Associate
Mark Chesnek, Media Relations Assistant
(202) 334-2138; e-mail <news at nas.edu>

FOR IMMEDIATE RELEASE 

Fruits and Vegetables Yield Less Vitamin A Than Previously Thought;
Upper Limit Set for Daily Intake of Vitamin A and Nine Other Nutrients

WASHINGTON -- Darkly colored, carotene-rich fruits and vegetables -- such as
carrots, sweet potatoes, and broccoli -- provide the body with half as much
vitamin A as previously thought, says the latest report on Dietary Reference
Intakes (DRIs) from the National Academies' Institute of Medicine. This
means people need to make sure they eat enough of these fruits and
vegetables to meet their daily requirement for vitamin A, especially if they
do not eat animal-derived foods, which serve as abundant sources of the
nutrient for most people.

"Darkly colored fruits and vegetables are still good sources of vitamin A,"
said Robert Russell, professor of medicine and nutrition, Tufts University
School of Medicine, Boston, and chair of the panel that wrote the report.
"But new evidence shows that it takes twice as much of them to yield the
same amount of vitamin A in the body as we previously understood. People
need to take this into consideration and make sure they select enough
carotene-rich fruits and vegetables to meet their daily vitamin A
requirement. This is especially true for those who don't eat meats, fish,
eggs, or vitamin A-fortified milk or cereal. They may need to significantly
increase their consumption of such fruits and vegetables."

Three carotenoids -- alpha-carotene, beta-carotene, and beta-cryptoxanthin
-- are present in certain orange, red, green, and dark-yellow fruits and
vegetables. They are referred to as provitamin A carotenoids because they
can be converted in the body to retinol, an active form of vitamin A. Based
on a comprehensive review of recent research, the panel found that the
amount of provitamin A carotenoids required to create a unit of retinol is
twofold higher than the amount believed needed in 1989, when the National
Academy of Sciences last issued recommendations for vitamin A.

In addition to vitamin A, the report examines the nutritional value of the
micronutrients vitamin K, arsenic, boron, chromium, copper, iodine, iron,
manganese, molybdenum, nickel, silicon, vanadium, and zinc. It sets a daily
maximum level of intake for vitamin A as well as for boron, copper, iodine,
iron, manganese, molybdenum, nickel, vanadium, and zinc. Specific
recommended intakes are given for vitamins A and K, chromium, copper,
iodine, iron, manganese, molybdenum, and zinc. 

New Dietary Recommendations

The new DRI report is the fifth in a series that updates and expands on the
Recommended Dietary Allowances (RDAs) in the United States and Recommended
Nutrient Intakes in Canada. Although DRIs are designed for use in the United
States and Canada, they can provide guidance to researchers and
policy-makers coping with malnutrition elsewhere in the world. For example,
while iron deficiency, especially among pregnant women, is of concern in
this country and Canada, it also is known to be prevalent -- along with
vitamin A, zinc, and iodine deficiencies -- in developing countries.

DRIs are established using a new paradigm based on indicators of good health
and the prevention of chronic disease developed by U.S. and Canadian
scientists. They encompass not only recommended daily intakes that are
intended to help people maintain their health, but also tolerable upper
intake levels (ULs) that help them avoid harm from taking too much of a
nutrient. An adequate intake (AI), based on diets known to be nutritionally
adequate for the U.S. and Canadian populations, is recommended when not
enough evidence exists to set an RDA. The reference intake values are
designed to meet the needs of individuals in the United States and in Canada
who are healthy and free from specific diseases or conditions that may alter
their daily nutritional requirements.

Based on national nutrition surveys, the report says that daily requirements
for the nutrients it examined can be met, in almost all instances, without
taking supplements. One exception, however, is that pregnant women usually
need iron supplements to meet their increased daily requirements. In fact,
surveys in the United States show that only half of all pregnant women who
live here consume adequate amounts of iron in their diets. 

Below are highlights of the report's recommendations. The full report
contains dietary recommendations -- when the data allows -- for all age
groups, as well as for pregnant and lactating women.

Vitamin A. Besides being important for normal vision, vitamin A plays a
vital role in gene expression, reproduction, embryonic development, growth,
and immune function. To ensure adequate stores of vitamin A in the body, men
should consume 900 micrograms daily and women should consume 700 micrograms
daily. The UL was set at 3 milligrams, or 3,000 micrograms, per day. Recent
research shows that excess vitamin A intake may increase the risk of
physical birth defects, liver abnormalities in adults, and bulging of the
skull where bone has not yet formed in infants and young children.

The most obvious symptom of inadequate vitamin A consumption is vision
impairment, especially night blindness, which occurs after the body's
vitamin A stores have been depleted. Up to 500,000 children worldwide go
blind each year because of vitamin A deficiency. Night blindness induced by
vitamin A deficiency is rarely observed in the United States and Canada, and
determining from survey data whether people in these two countries get
enough vitamin A is more difficult. For example, estimates of intake from
national surveys of food and nutrient consumption indicate that between 25
percent and 50 percent of young adults in the United States may not get
enough of the nutrient in their diets to assure adequate vitamin A stores.
However, these figures should be interpreted with caution since the surveys
only measure consumption over one or two days, when in fact it takes several
weeks of data collection to accurately assess intake of this vitamin. 

Vitamin K. This nutrient plays an essential role in the coagulation of blood
and is found in green leafy vegetables. An AI of 120 micrograms for men and
90 micrograms for women was determined based on consumption levels of
healthy individuals. No adverse effects have been reported for vitamin K, so
a UL was not established. There have been reports that a lack of the vitamin
may be related to bone disease, including the development of osteoporosis,
but the panel concluded there is not sufficient evidence to firmly establish
a relationship. 

Chromium. A number of studies have shown that chromium stimulates insulin
action in the body. However, the daily requirement for chromium could not be
established because not enough information exists to determine a
relationship between a particular dose of the nutrient and insulin response.
Not all studies show that chromium supplementation has a positive effect on
the regulation of glucose levels, the report notes. Based on current
estimated consumption by the general population, an AI of 35 micrograms for
men and 25 micrograms for women was recommended. Chromium is widely
distributed throughout the food supply. Few serious side effects have been
associated with excess intake of chromium from food, and little data are
available on adverse effects resulting from chronically high intake of the
chromium contained in supplements, so no UL was set. Some forms of chromium
are known to be toxic, but those are not present naturally in foods or
contained in currently available dietary supplements.

Copper. The new RDA for copper -- a nutrient necessary for proper
development of connective tissue, nerve coverings, and skin pigment -- is
900 micrograms a day for both men and women. To protect against possible
liver damage, the UL was set at 10 milligrams per day. Copper is widely
distributed in foods such as organ meats, seafood, nuts, and seeds; some
foods that are consumed in substantial amounts, such as milk, tea, chicken,
and potatoes, also contain the nutrient, but at lower levels.

Iodine. Iodine is an important component of thyroid hormones and is stored
in the thyroid gland. A deficiency can cause mental retardation,
hypothyroidism, goiter, and dwarfism. Based on research into how much iodine
the thyroid needs to properly regulate enzyme and metabolic processes, an
RDA of 150 micrograms a day was established for both men and women. Most
food sources have little iodine, though some plants grown in iodine-rich
soil and seafood have higher concentrations because they absorb the nutrient
from their environments. Iodized salt also is a dietary source. To avoid
over-absorption of iodine by the thyroid, adults should not consume more
than the UL of 1.1 milligrams daily. 

Iron. Iron is vital for transporting oxygen in the bloodstream and for the
prevention of anemia. Even more of the nutrient is needed during periods of
growth and for the fetus during pregnancy. Women during pre-menopause years
also need more, since iron is lost through menstruation. The report sets the
RDA for men and post-menopausal women at 8 milligrams per day, and at 18
milligrams for pre-menopausal women. Pregnant women should consume 27
milligrams a day, which usually requires taking a small supplement since it
is difficult to get that much iron through diet alone. The RDA for women who
breast-feed and are not menstruating is 9 milligrams a day; for adolescents
who breast-feed, it is 10 milligrams daily. Human milk only provides enough
iron for infants until they are 6 months old, so the report recommends that
older infants -- those between the ages of 7 months and 12 months -- who are
breast-fed be given foods or formula containing additional iron; older
infants receiving formula also should be given iron-fortified formula or
foods. Oral contraceptives reduce menstrual blood losses, so women taking
them need less daily iron. Post-menopausal women who are on hormone
replacement therapy should consume more iron because the therapy often
causes periodic uterine bleeding. Because the absorption of iron from plant
foods is low compared to that from animal foods, vegetarians need to consume
twice as much iron to meet their daily requirement.

The UL for iron is set at 45 milligrams a day for adults, above which
gastrointestinal distress may occur, especially when consuming iron
supplements on an empty stomach. Research has suggested a possible link
between elevated iron stores and a higher incidence of heart disease and
cancer. However, the report says that evidence for a relationship between
dietary iron intake and increased risk of these diseases is inconclusive. In
addition, individuals who inherit both genes for hereditary hemochromatosis,
an iron absorption disorder, are at increased risk for accumulating harmful
amounts of iron. The tolerable upper intake level was not set to protect
these people since there is insufficient evidence to determine a specific
maximum level that would provide significant protection against the
development of the clinical symptoms of this disorder.

Manganese. This nutrient is involved in bone formation and in protein, fat,
and carbohydrate metabolism. Nuts, legumes, tea, and whole grains are rich
sources of manganese. The report sets an adequate intake level for manganese
at 2.3 milligrams per day for men and 1.8 milligrams per day for women. The
UL is set at 11 milligrams for adults, based on a recent study showing that
no adverse health effects occurred when this amount was consumed on a
chronic basis. Neurological side effects, similar to symptoms caused by
Parkinson's disease, were observed in an earlier study among participants
who consumed 15 milligrams a day.

Molybdenum. The new RDA for molybdenum is 45 micrograms per day for both men
and women. Sources of this enzyme-enhancing nutrient include legumes, grain
products, and nuts. The UL was set at 2 milligrams, based on studies showing
impaired reproduction and growth in animals at high levels of chronic
intake.

Zinc. Zinc is associated with more than 100 specific enzymes and is vital
for protein function and gene expression. Many breakfast cereals are
fortified with zinc and it is naturally abundant in red meats, certain
seafood, and whole grains. The RDA for zinc was set at 11 milligrams per day
for men and 8 milligrams per day for women. Vegetarians may need up to 50
percent more, however, since a chemical in plants, called phytate, as well
as calcium, hinder zinc absorption in the body. As is the case with iron,
human milk does not contain enough zinc for older infants between the ages
of 7 months and 12 months to meet their RDA, so children this age should
consume foods containing this nutrient if they consume human milk or be
given formula containing zinc. A UL of 40 milligrams for adults was set,
based on studies showing that zinc adversely affects copper absorption at
high levels of intake.

Arsenic, Boron, Nickel, Silicon, and Vanadium. Although there is some
evidence suggesting a beneficial role for these elements in animal and human
health, not enough data exist to define with certainty what their specific
roles may be. Therefore, recommended intake levels were not established.
However, based on adverse effects noted in animal studies, tolerable upper
intake levels were set for boron at 20 milligrams per day; for vanadium at
1.8 milligrams per day; and for nickel at 1 milligram per day. Arsenic in
chemical forms is a known toxic element, but not enough data exist on
chronic intakes at lower levels from food and supplements to set a UL. Data
also were lacking upon which to base a UL for silicon. 

A Research Agenda

The report identifies several gaps in what is known about these 14
micronutrients. For example, there is a dearth of studies designed
specifically to estimate average nutrient requirements for healthy humans,
especially infants, children, adolescents, the elderly, and pregnant women.
In addition, there has been a lack of research aimed at studying the role of
these micronutrients in reducing the risk of chronic diseases or detecting
side effects from chronic overconsumption. High priority should be given to
research that attempts to fill in this missing information, including
studies to further identify factors that impair or enhance the absorption
and metabolism of these nutrients and to further investigate the role of
arsenic, boron, nickel, silicon, and vanadium in human health. 

The study was sponsored by the U.S. Department of Health and Human Services;
the National Institutes of Health; the Centers for Disease Control and
Prevention; Health Canada; the Institute of Medicine; the Dietary Reference
Intakes Private Foundation Fund, including the Dannon Institute and the
International Life Sciences Institute; and the Dietary Reference Intakes
Corporate Donors' Fund, which includes contributions from Roche Vitamins
Inc., Mead Johnson Nutrition Group, Nabisco Foods Group, U.S. Borax, Daiichi
Fine Chemicals Inc., Kemin Foods Inc., M&M/Mars, Weider Nutrition Group, and
the Natural Source Vitamin E Association. 

The study was undertaken by a group of more than 40 scientists from the
United States and Canada under the auspices of the Institute of Medicine's
Food and Nutrition Board. The Institute is a private, nonprofit organization
that provides health policy advice under a congressional charter granted to
the National Academy of Sciences.

Copies of Dietary Reference Intakes for Vitamin A, Vitamin K, Arsenic,
Boron, Chromium, Copper, Iodine, Iron, Manganese, Molybdenum, Nickel,
Silicon, Vanadium, and Zinc will be available later this year from the
National Academy Press at the mailing address in the letterhead; tel. (202)
334-3313 or 1-800-624-6242. Reporters may obtain a pre-publication copy from
the Office of News and Public Information at the letterhead address
(contacts listed above).