Below are the first 10 and last 10 pages of uncorrected machine-read text (when available) of this chapter, followed by the top 30 algorithmically extracted key phrases from the chapter as a whole.
Intended to provide our own search engines and external engines with highly rich, chapter-representative searchable text on the opening pages of each chapter.
Because it is UNCORRECTED material, please consider the following text as a useful but insufficient proxy for the authoritative book pages.
Do not use for reproduction, copying, pasting, or reading; exclusively for search engines.
OCR for page 362
TABLE 1 Dietary Reference Intakes for Phosphorus by
Life Stage Group
DRI values (mg /day)
EARa RDAb AIc ULd
males females males females
Life stage group
NDe
0 through 6 mo 100
7 through 12 mo 275 ND
1 through 3 y 380 380 460 460 3,000
4 through 8 y 405 405 500 500 3,000
9 through 13 y 1,055 1,055 1,250 1,250 4,000
14 through 18 y 1,055 1,055 1,250 1,250 4,000
19 through 30 y 580 580 700 700 4,000
31 through 50 y 580 580 700 700 4,000
51 through 70 y 580 580 700 700 4,000
> 70 y 580 580 700 700 3,000
Pregnancy
£ 18 y 1,055 1,250 3,500
19 through 50 y 580 700 3,500
Lactation
£ 18 y 1,055 1,250 4,000
19 through 50 y 580 700 4,000
a EAR = Estimated Average Requirement.
b RDA = Recommended Dietary Allowance.
c AI = Adequate Intake.
d UL = Tolerable Upper Intake Level. Unless otherwise specified, the UL represents
total intake from food, water, and supplements.
e ND = Not determinable. This value is not determinable due to the lack of data of
adverse effects in this age group and concern regarding the lack of ability to handle
excess amounts. Source of intake should only be from food to prevent high levels of
intake.
OCR for page 363
PART III: PHOSPHORUS 363
PHOSPHORUS
T
he element phosphorus is found in nature (e.g., foods, water, and living
tissues) primarily as phosphate (PO4). It is a major component of bones
and teeth. In fact, 85 percent of total body phosphorus is found in bone.
Phosphorus helps maintain a normal pH in the body and is involved in meta-
bolic processes.
The adult requirements for phosphorus are based on studies of serum inor-
ganic phosphate concentration in adults. The Tolerable Upper Intake Level (UL)
was derived using data on the normal adult range for serum inorganic phos-
phate concentration. DRI values are listed by life stage group in Table 1.
Nearly all foods contain phosphorus, and it is also common in food addi-
tives. Phosphorus deficiency is generally not a problem; the average adult diet
contains about 62 mg phosphorus per 100 kcal. Excess phosphorus intake is
expressed as hyperphosphatemia, and essentially all adverse effects of phos-
phorus excess are due to the elevated inorganic phosphorus in the extracellular
fluid (ECF).
PHOSPHORUS AND THE BODY
Function
Phosphorus is a major component of bones and teeth. Its main functions are to
maintain a normal pH (by buffering excesses of acid or alkali), temporarily
store and transfer energy derived from metabolic fuels, and activate catalytic
proteins via phosphorylation. Structurally, phosphorus occurs in the body as
phospholipids (a major component of biological membranes) and as nucle-
otides and nucleic acids. Dietary phosphorus supports tissue growth and re-
places phosphorus stores that are lost through excretion and the shedding of
skin cells.
Absorption, Metabolism, Storage, and Excretion
Phosphorus found in foods is a mixture of organic and inorganic forms, and
most phosphorus absorption occurs as inorganic phosphate. Approximately
55–70 percent of dietary phosphorus is absorbed in adults and about 65–90
percent in infants and children. The majority of phosphorus absorption occurs
through passive concentration-dependent processes.
OCR for page 364
DRIs: THE ESSENTIAL GUIDE TO NUTRIENT REQUIREMENTS
364
The amount of phosphorus ingested does not appear to affect absorption
efficiency, which suggests that this efficiency does not improve with low intakes
(unlike calcium absorption). By the same token, when serum phosphorus is
abnormally high, even dangerously so, phosphorus continues to be absorbed
from the diet at a rate only slightly lower than normal. Phosphorus absorption
is reduced by aluminum-containing antacids and pharmacological doses of cal-
cium carbonate. However, when consumed at intakes in the typical adult range,
calcium does not significantly interfere with phosphorus absorption.
In adults, 85 percent of phosphorus is found in bone, with the remaining
15 percent distributed through the soft tissues. Excretion is achieved mainly
through the kidneys. In healthy adults, the amount of phosphorus excreted in
the urine is essentially equal to the amount absorbed through diet, less small
amounts lost in the shedding of skin cells and intestinal mucosa.
DETERMINING DRIS
Determining Requirements
The adult requirements for phosphorus are based on studies of serum inor-
ganic phosphate concentration.The EAR, and hence the RDA, for healthy ado-
lescents aged 9 through 18 years is based on a factorial approach and is higher
than the adult value. This is because this age range brackets a period of intense
growth, with growth rate, absorption efficiency, and normal values of inorganic
phosphorus in the extracellular fluid changing during this time.
Criteria for Determining Phosphorus Requirements,
by Life Stage Group
Life stage group Criterion
0 through 12 mo Human milk content
1 through 18 y Factorial approach
19 through 50 y Serum Pi (serum inorganic phosphate concentration)
51 through > 70 y Extrapolation of serum Pi from 19 through 50 years
Pregnancy
£ 18 y Factorial approach
19 through 50 y Serum Pi
Lactation
£ 18 y Factorial approach
19 through 50 y Serum Pi
OCR for page 365
PART III: PHOSPHORUS 365
The UL
The Tolerable Upper Intake Level (UL) is the highest level of daily nutrient
intake that is likely to pose no risk of adverse effects for almost all people.
Members of the general population should not routinely exceed the UL. The
UL value for phosphorus was derived using data on the normal adult range for
serum inorganic phosphate concentration and represents total intake from food,
water, and supplements.
Phosphorus exposure data, based on data from the Continuing Survey of
Food Intakes by Individuals (CSFII, 1994–1996) and the 1986 National Health
Interview Survey (NHIS), indicated that only a small percentage of the popula-
tion was likely to routinely exceed the UL for phosphorus; however, because
food composition data do not always indicate phosphorus from food additives,
the full extent of phosphorus intake is not known.
DIETARY SOURCES
Foods
Phosphorus is found naturally in many foods in the form of phosphate (PO4)
and as a food additive in the form of various phosphate salts, which are used for
nonnutrient functions during food processing, such as moisture retention,
smoothness, and binding.
According to data from the National Health Survey (1976–1980), the phos-
phorus content of the average adult diet for both men and women is about 62
mg/100 kcal. Dietary intake of phosphorus appears to be affected more by total
food intake and less by differences in food composition. People with a high
intake of dairy products will have diets with higher phosphorus density values
because the phosphorus density of cow milk is higher than for most other foods.
People who consume several servings per day of colas or a few other soft drinks
that contain phosphoric acid also tend to have high phosphorus intake. A 12-
ounce serving of such beverages contains about 50 mg, which is only 5 percent
of the typical intake by an adult woman. However, when consumed in a quan-
tity of 5 or more servings per day, such beverages may contribute substantially
to total phosphate intake.
Dietary Supplements
Phosphorus supplements are not widely used in the United States. Based on the
1986 NHIS study, about 10 percent of adults and 6 percent of children aged 2
to 6 years took supplements containing phosphorus. Supplement usage and
OCR for page 366
DRIs: THE ESSENTIAL GUIDE TO NUTRIENT REQUIREMENTS
366
dosage was similar for men and women, with a median intake from supple-
ments of 120 mg/day.
Bioavailability
Most foods exhibit good phosphorus bioavailability. However, foods derived
from plant seeds (e.g., beans, peas, cereals, and nuts) contain phytic acid (also
called phytate), a stored form of phosphorus that is not directly available to
humans. Absorption of this form requires the presence of phytase, an enzyme
found in some foods and in some colonic bacteria. Because yeasts can hydro-
lyze phytate, whole grains that are incorporated into leavened bread products
have higher phosphorus bioavailability than do grains used in unleavened bread
or breakfast cereals. Also, unabsorbed calcium in the digestive tract combines
with phytic acid and interferes with its digestion and absorption. This may
partly explain why calcium interferes with phosphorus absorption.
In infants, phosphorus bioavailability is highest from human milk (85–90
percent), intermediate from cow milk (72 percent), and lowest from soy formu-
las, which contain phytic acid (59 percent). However, the higher amounts of
phosphorus contained in cow milk and soy formulas offset this decreased
bioavailability.
Dietary Interactions
There is evidence that phosphorus may interact with certain nutrients and di-
etary substances (see Table 2).
INADEQUATE INTAKE AND DEFICIENCY
Phosphorus deficiency is generally not a problem. This is because phosphorus
is so ubiquitous in the diet that near total starvation is required to produce
dietary phosphorus deficiency. However, if inadequate phosphorus intake does
occur, such as in individuals recovering from alcoholic bouts, from diabetic
ketoacidosis, and from refeeding with calorie-rich sources without paying at-
tention to phosphorus needs, it is realized as hypophosphatemia. The effects of
hypophosphatemia include the following:
• Anorexia
• Anemia
• Muscle weakness
• Bone pain
• Rickets (in children) and osteomalacia (in adults)
• General debility
OCR for page 367
PART III: PHOSPHORUS 367
TABLE 2 Potential Interactions with Other Dietary Substances
Substance Potential Interaction Notes
SUBSTANCES THAT AFFECT PHOSPHORUS
Calcium Pharmacological doses of Calcium in the normal adult intake range is not likely
calcium carbonate may to pose a problem for phosphorus absorption.
interfere with phosphorus
absorption.
Aluminum When taken in large doses,
antacids that contain
aluminum may interfere with
phosphorus absorption.
PHOSPHORUS AFFECTING OTHER SUBSTANCES
Calcium Excess intake of phosphorus This is less likely to pose a problem if calcium intake is
may interfere with calcium adequate.
absorption.
• Increased susceptibility to infection
• Paresthesias
• Ataxia
• Confusion
• Possible death
Special Considerations
Antacids: Antacids that contain aluminum can bind with dietary phosphorus
and, when consumed in large doses, produce hypophosphatemia.
Treating malnutrition: The refeeding of energy-depleted individuals, either orally
or parenterally, must supply adequate inorganic phosphate. Otherwise, severe
and perhaps fatal hypophosphatemia may occur.
EXCESS INTAKE
Excess phosphorus intake from any source can result in hyperphosphatemia,
the adverse effects of which are due to an elevated concentration of inorganic
phosphate in the extracellular fluid. Hyperphosphatemia from dietary causes
becomes a problem mainly in individuals with end-stage renal disease or in
such conditions as vitamin D intoxication. The potential effects of
hyperphosphatemia include the following:
OCR for page 368
DRIs: THE ESSENTIAL GUIDE TO NUTRIENT REQUIREMENTS
368
• Reduced calcium absorption (less problematic with adequate calcium
intake)
• Calcification of nonskeletal tissues, particularly the kidneys
Concern about high phosphorus intake has been raised because of a probable
population-level increase in phosphorus intake through colas and a few other
soft drinks that contain phosphoric acid and processed foods containing phos-
phate additives. High intakes of polyphosphates found in additives may inter-
fere with the absorption of iron, copper, and zinc. However, further research is
necessary in this area.
OCR for page 369
PART III: PHOSPHORUS 369
KEY POINTS FOR PHOSPHORUS
The element phosphorus is found in nature primarily as
3
phosphate (PO4). It is a major component of bones and teeth.
In fact, 85 percent of total body phosphorus is found in bone.
Phosphorus helps maintain a normal pH in the body and is
3
involved in metabolic processes. Dietary phosphorus supports
tissue growth and replaces phosphorus stores that are lost
through excretion and the shedding of skin cells.
The adult requirements for phosphorus are based on studies of
3
serum inorganic phosphate concentration. The UL was derived
using data on the normal adult range for serum inorganic
phosphate concentration.
Nearly all foods contain phosphorus; dairy products are a
3
particularly rich source.
Foods derived from plant seeds (e.g., beans, peas, cereals,
3
and nuts) contain phytic acid (also called phytate), a stored
form of phosphorus that is poorly absorbed in humans.
Phosphorus deficiency is generally not a problem; the average
3
adult diet contains about 62 mg phosphorus per 100 kcal.
Excess phosphorus intake from any source can result in
3
hyperphosphatemia, the adverse effects of which are due to an
elevated concentration of inorganic phosphate in the
extracellular fluid. Hyperphosphatemia from dietary causes
becomes a problem mainly in individuals with end-stage renal
disease or in such conditions as vitamin D intoxication.
There is concern about the population-level increase in
3
phosphorus intake through colas and a few other soft drinks
that contain phosphoric acid and processed foods containing
phosphates. High intakes of polyphosphates found in additives
may interfere with the absorption of iron, copper, and zinc.
However, further research is necessary in this area.
