Livro DRI 2006 (Micronutrientes)

Livro DRI 2006 (Micronutrientes)


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Copyright © National Academy of Sciences. All rights reserved.
Dietary Reference Intakes: The Essential Guide to Nutrient Requirements
http://www.nap.edu/catalog/11537.html
164 DRIs: THE ESSENTIAL GUIDE TO NUTRIENT REQUIREMENTS
TABLE 2 Potential Substances That Affect Water Requirements
Substance Potential Interaction Notes
SUBSTANCES THAT AFFECT WATER REQUIREMENTS
Caffeine Due to its diuretic effect, Available data were inconsistent. Unless future
caffeine in high amounts research proves otherwise, caffeinated beverages
may lead to a total body appear to contribute to total water intake to the
water (TBW) deficit. same degree as noncaffeinated fluids do.
Alcohol Alcohol intake appears to Based on limited data, ethanol ingestion did not
increase water excretion. appear to result in appreciable fluid loss over
a 24-hour period. An increased excretion of
water due to ethanol ingestion was transient.
Sodium Increased sodium intake Based on limited data, it was not possible to
may increase urine volume. determine the extent to which sodium intake
influences water intake.
Protein Increased protein Studies showed that increased protein intake did
consumption may increase not affect water intake or urine volume in
water needs. Urea, a major the setting of ad libitum water consumption.
end product of the
metabolism of dietary
proteins and amino acids,
requires water for excretion
by the kidneys.
Fiber Fecal water loss is increased Limited studies showed significant increases in
with increased dietary fiber. fecal water loss with high-fiber diets.
Carbohydrate The presence of dietary On average, 100 g/day of carbohydrates (the amount
carbohydrates may affect needed to prevent ketosis) has been shown to
decrease body water deficit by decreasing the
quantity of body solutes (ketone bodies) that need to
be excreted. This response is similar when ketosis
occurs with the consumption of very low
carbohydrate diets.
Copyright © National Academy of Sciences. All rights reserved.
Dietary Reference Intakes: The Essential Guide to Nutrient Requirements
http://www.nap.edu/catalog/11537.html
PART II: WATER 165
\u2022 Impaired ability to maintain blood pressure when presented with vas-
cular challenges
\u2022 Fainting (in susceptible people)
\u2022 Reduced cardiac output during exercise and heat stress
\u2022 Apparent increased risk of life-threatening heat stroke
EXCESS INTAKE
No adverse effects have been reported with chronic high intakes of water by
healthy people who consume a normal diet, as long as fluid intake is approxi-
mately proportional to fluid loss. Excessive water intake can lead to hyponatre-
mia, which is a low concentration of sodium in the blood (defined as serum
sodium concentration of less than 135 mmol/L). The lowering of the extracel-
lular fluid sodium concentration causes fluid to move into the intracellular fluid
space, resulting in central nervous system edema, lung congestion, and muscle
weakness. Hyponatremia can also occur from excessive fluid intake, the under-
replacement of sodium, or both, during or after prolonged endurance athletic
events. In severe cases, hyponatremia can be life-threatening.
Hyponatremia is rare in healthy persons who consume an average North
American diet. The condition is most often seen in infants, psychiatric patients
with psychogenic polydipsia (chronic excessive thirst and fluid intake), pa-
tients on psychotropic drugs, women who have undergone surgery using a uter-
ine distension medium, and participants in prolonged endurance events, such
as military recruits.
A series of case studies has suggested that gross overconsumption of fluids
(for example, more than 20 L/day) is associated with irreversible bladder le-
sions and possibly thinner bladder muscles, delayed bladder sensation, and
flow rate impairment.
Copyright © National Academy of Sciences. All rights reserved.
Dietary Reference Intakes: The Essential Guide to Nutrient Requirements
http://www.nap.edu/catalog/11537.html
166 DRIs: THE ESSENTIAL GUIDE TO NUTRIENT REQUIREMENTS
KEY POINTS FOR WATER
3 Water, vital for life, is essential for cellular homeostasis and for
maintaining vascular volume. It also serves as the medium for
transport within the body by supplying nutrients and removing
waste.
3 Since data were insufficient to establish an EAR and thus
calculate an RDA for water, an AI was instead developed.
3 The AIs for water are based on the median total water intake
from U.S. survey data. These reference values represent total
water intakes that are considered likely to prevent deleterious,
primarily acute, effects of dehydration, including metabolic and
functional abnormalities.
3 Although a low intake of total water has been associated with
some chronic diseases, this evidence is insufficient to establish
water intake recommendations as a means to reduce the risk
of chronic diseases.
3 Over the course of a few hours, body water deficits can occur
due to reduced intake or increased water loss from physical
activity and environmental (heat) exposure. However, on a day-
to-day basis, fluid intake, driven by the combination of thirst
and mealtime beverage consumption, helps maintain hydration
status and total body water at normal levels.
3 Because healthy individuals have a considerable ability to
excrete excess water and thereby maintain water balance, a UL
was not set for water.
3 Acute water toxicity has been reported from the rapid
consumption of large quantities of fluids that greatly exceeded
the kidneys\u2019 maximal excretion rate of approximately 0.7\u20131.0 L/
hour.
3 Sources of water include drinking water, beverages, and food.
3 Inadequate water intake leads to dehydration, which can impair
mental function, exercise performance, exercise and heat
stress tolerance, and blood pressure regulation.
3 Excessive water intake can lead to hyponatremia, which is a
low concentration of sodium in the blood. This condition leads
to central nervous system edema, lung congestion, and muscle
weakness.
Copyright © National Academy of Sciences. All rights reserved.
Dietary Reference Intakes: The Essential Guide to Nutrient Requirements
http://www.nap.edu/catalog/11537.html
PART III: VITAMINS AND MINERALS 167
PART III
VITAMINS AND MINERALS
Part Three of this publication summarizes information from the DRI re-ports titled Dietary Reference Intakes for Vitamin C, Vitamin E, Selenium,and Carotenoids (2000); Dietary Reference Intakes for Water, Potassium, So-
dium, Chloride, and Sulfate (2005); Dietary Reference Intakes for Calcium, Phos-
phorus, Magnesium, Vitamin D, and Fluoride (1997); Dietary Reference Intakes for
Thiamin, Riboflavin, Niacin, Vitamin B
6
, Folate, Vitamin B
12
, Pantothenic Acid, Bi-
otin, and Choline (1998); and Dietary Reference Intakes for Vitamin A, Vitamin K,
Arsenic, Boron, Chromium, Copper, Iodine, Iron, Manganese, Molybdenum, Nickel,
Silicon, Vanadium, and Zinc (2001). This section is divided into chapters that are
organized by nutrient for 35 individual vitamins and minerals. Each chapter
provides a table of known nutrient reference values; reviews the function of a
given nutrient in the human body; summarizes the known effects of deficien-
cies and excessive intakes; describes how a nutrient may be related to chronic
disease or developmental abnormalities, where data were available; and pro-
vides the indicator of adequacy for determining the nutrient requirements.
Vitamins covered in Part Three include vitamin A, vitamin B
6
, vitamin B
12
,
biotin, vitamin C, carotenoids, choline, vitamin D, vitamin E, folate, vitamin K,
niacin, pantothenic acid, riboflavin, and thiamin. Minerals covered in Part Three
include calcium, chromium, copper, fluoride, iodine, iron, magnesium, man-
ganese, molybdenum, phosphorus,