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 386
TABLE 1 Dietary Reference Intakes for Sodium and Chloride
by Life Stage Group
DRI values (g/day)
Sodium Chloride
AIa ULb AI UL
Life stage groupc
NDd
0 through 6 mo 0.12 0.18 ND
7 through 12 mo 0.37 ND 0.57 ND
1 through 3 y 1.0 1.5 1.5 2.3
4 through 8 y 1.2 1.9 1.9 2.9
9 through 13 y 1.5 2.2 2.3 3.4
14 through 18 y 1.5 2.3 2.3 3.6
19 through 30 y 1.5 2.3 2.3 3.6
31 through 50 y 1.5 2.3 2.3 3.6
51 through 70 y 1.3 2.3 2.0 3.6
> 70 y 1.2 2.3 1.8 3.6
Pregnancy
£18 y 1.5 2.3 2.3 3.6
19 through 50 y 1.5 2.3 2.3 3.6
Lactation
£18 y 1.5 2.3 2.3 3.6
19 through 50 y 1.5 2.3 2.3 3.6
a AI = Adequate Intake.
b UL = Tolerable Upper Intake Level. Unless otherwise specified, the UL represents
total intake from food, water, and supplements.
c All groups except Pregnancy and Lactation represent males and females.
d 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 387
PART III: SODIUM AND CHLORIDE 387
SODIUM CHLORIDE
AND
S
odium and chloride are necessary to maintain extracellular fluid volume
and plasma osmolality. The cation sodium and the anion chloride are
normally found in most foods together as sodium chloride (salt). For this
reason, this publication presents data on the requirements for and the effects of
sodium and chloride together.
Since data were inadequate to determine Estimated Average Requirements
(EARs) and thus calculate Recommended Dietary Allowances (RDAs) for so-
dium and chloride, Adequate Intakes (AIs) were instead developed. The AIs for
sodium are set at an intake that ensures that the overall diet provides an ad-
equate intake of other important nutrients and covers sodium sweat losses in
unacclimated individuals who are exposed to high temperatures or who be-
come physically active. The AIs for chloride are set at a level equivalent on a
molar basis to that of sodium, since almost all dietary chloride comes with
sodium added during the processing or consumption of foods. The AIs for
sodium do not apply to individuals who lose large volumes of sodium in sweat,
such as competitive athletes and workers exposed to extreme heat stress (e.g.,
foundry workers and firefighters).
The adverse effects of higher levels of sodium intake on blood pressure
provide the scientific rationale for setting the Tolerable Upper Intake Level (UL)
for sodium and chloride. DRI values are listed by life stage group in Table 1.
In the United States, sodium chloride accounts for about 90 percent of
total sodium intake in the United States. Most of the sodium chloride found in
the typical diet is added to food during processing. Examples of high-sodium
processed foods include luncheon meats and hot dogs, canned vegetables, pro-
cessed cheese, potato chips, Worcestershire sauce, and soy sauce.
Overall, there is little evidence of any adverse effect of low dietary sodium
intake on serum or plasma sodium concentrations in healthy people. Likewise,
chloride deficiency is rarely seen because most foods that contain sodium also
provide chloride. The primary adverse effect related to increased sodium chlo-
ride intake is elevated blood pressure, which is directly related to cardiovascu-
lar disease and end-stage renal disease. Individuals with hypertension, diabe-
tes, and chronic kidney disease, as well as African Americans and older people,
tend to be more sensitive than others to the blood pressure–raising effect of
sodium chloride intake.
OCR for page 388
DRIs: THE ESSENTIAL GUIDE TO NUTRIENT REQUIREMENTS
388
SODIUM AND CHLORIDE AND THE BODY
Function
About 95 percent of the body’s sodium content is found in the extracellular
fluid, where it serves as the primary cation. Sodium regulates extracellular fluid
volume and plasma volume and also plays an important role in the membrane
potential of cells (the electrical potential difference across a cell’s plasma mem-
brane) and the active transport of molecules across cell membranes.
Chloride, in association with sodium, is the primary osmotically active
anion in the extracellular fluid. It plays a key role in maintaining fluid and
electrolyte balance. In addition, chloride, in the form of hydrochloric acid, is an
important component of gastric juice.
Absorption, Metabolism, Storage, and Excretion
Sodium and chloride ions are typically consumed as sodium chloride. About
98 percent of ingested sodium chloride is absorbed, mainly in the small intes-
tine. Absorbed sodium and chloride remain in the extracellular compartments,
which include the plasma, interstitial fluid, and plasma water. As long as sweat-
ing is not excessive, most of this sodium chloride is excreted in the urine. In
people with “steady-state” sodium and fluid balance, and minimal sweat loss,
the amount of sodium excreted in urine is roughly equal to the amount con-
sumed, when other obligatory sodium losses are small.
A number of systems and hormones influence sodium and chloride bal-
ance, some of which are shown in Table 2.
DETERMINING DRIS
Determining Requirements
Since data were inadequate to determine EARs and thus calculate RDAs for
sodium and chloride, AIs were instead developed. The AIs for sodium are set at
an intake that ensures that the overall diet provides an adequate intake of other
important nutrients and also covers sodium sweat losses in unacclimated indi-
viduals who are exposed to high temperatures or who become physically active
(as recommended in Part II, “Physical Activity”). The AIs for chloride are set at
a level equivalent on a molar basis to that of sodium, since almost all dietary
chloride comes with the sodium added during processing or consumption of
foods.
Concerns have been raised that a low level of sodium intake adversely
affects blood lipids, insulin resistance, and cardiovascular disease risk. How-
ever, at the level of the AI, the preponderance of evidence does not support this
OCR for page 389
PART III: SODIUM AND CHLORIDE 389
TABLE 2 Major Systems and Hormones That Influence Sodium Chloride
Balance
System or Hormones Activators Effect
Renin-angiotensin- • Reduced salt intake • Promotes retention of sodium
aldosterone axis • Reduced blood volume and chloride by the kidneys
• Reduced blood pressurea • Promotes renal reabsorption
of sodium
Atrial natriuretic peptide • Elevated blood volume • Increases glomerular filtration
(counter-regulatory system • Increased salt intake rate
to renin-angiotensin- • Increased blood pressure • Reduces blood volume
aldosterone axis) • Reduces blood pressure
• Increases sodium excretion
Sympathetic nervous • Reduced salt intake • Reduces sodium reabsorption
system • Reduced blood volume • Reduces water reabsorption in
• Reduced blood pressure the kidneys
a When the renin-angiotensin-aldosterone system is less responsive, as with advanced age, a greater
decrease in blood pressure results from reduced sodium chloride intake.
contention. A potential indicator of an adverse effect of inadequate sodium is
an increase in plasma renin activity. However, in contrast to the well-accepted
benefits of blood pressure reduction, the clinical relevance of modest rises in
plasma renin activity as a result of sodium reduction is uncertain.
It is well recognized that the current intake of sodium for most individuals
in the United States and Canada greatly exceeds both the AI and the UL. Progress
in achieving a reduced sodium intake will likely be gradual, requiring changes
in personal behavior toward salt consumption, which includes the replacement
of high sodium foods with lower sodium alternatives, as well as increased col-
laboration between the food industry and public health officials. Also required
will be a broad spectrum of additional research that includes the development
of reduced sodium foods that maintain flavor, texture, consumer acceptability,
and low cost.
Special Considerations
Excessive sweat loss: The AI for sodium does not apply to individuals who lose
large volumes of sodium in sweat, such as competitive athletes and workers
exposed to extreme heat stress (e.g., foundry workers and firefighters).
OCR for page 390
DRIs: THE ESSENTIAL GUIDE TO NUTRIENT REQUIREMENTS
390
Criteria for Determining Sodium and Chloride
Requirements, by Life Stage Group
Life stage group Criterion
0 through 6 months Average consumption of sodium from human milk
7 through 12 months Average consumption of sodium from human milk
+ complementary foods
1 through 18 y Extrapolation of adult AI based on median energy intake level
from CSFII
19 though 50 y Intake level to cover possible daily losses, provide adequate
intakes of other nutrients, and maintain normal function
> 50 y Extrapolation from younger adults based on median
energy intake level from CSFII
Pregnancy
< 18 through 50 y Age-specific AI
Lactation
< 18 through 50 y Age-specific AI
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
major adverse effect of increased sodium chloride intake is elevated blood pres-
sure. High blood pressure has been shown to be a risk factor for heart disease,
stroke, and kidney disease.
The scientific rationale for setting the UL is based on the impact of sodium
on blood pressure and represents total intake from food, water, and supple-
ments. However, because the relationship between sodium intake and blood
pressure is progressive and continuous without an apparent threshold, it is
difficult to precisely set a UL, especially since other environmental factors
(weight, exercise, potassium intake, dietary pattern, and alcohol intake) and
genetic factors also affect blood pressure. There was inadequate evidence to
support a different upper level of sodium intake in pregnant women from that
of nonpregnant women as a means to prevent hypertensive disorders of preg-
nancy.
Data from the Third National Health and Nutrition Examination Survey
(NHANES III, 1988–1994) indicated that more than 95 percent of men and 75
percent of women in the United States consumed sodium chloride in excess of
the UL. According to NHANES III, 24.7 percent of men and 24.3 percent of
OCR for page 391
PART III: SODIUM AND CHLORIDE 391
women aged 18 years and older had hypertension, indicating that a substantial
number of individuals appear to experience this adverse effect.
Data on Canadian consumption indicated that 90–95 percent of younger
men (aged 19 to 50 years) and between 50 and 75 percent of younger women
in the same age range had usual intakes above the UL. Neither of these surveys
included discretionary salt usage (e.g., from the salt shaker).
Special Considerations:
Sensitive individuals: The UL may be even lower for people whose blood pres-
sure is most sensitive to increased sodium intake (e.g., older people; African
Americans; and individuals with hypertension, diabetes, or chronic kidney dis-
ease) and who also have an especially high incidence of heart disease related to
high blood pressure.
Physical activity and temperature: In contrast, people unaccustomed to pro-
longed strenuous physical activity in a hot environment may have sodium needs
that exceed the UL because of sodium loss through sweat.
DIETARY SOURCES OF SODIUM AND
CHLORIDE
Foods
Sodium chloride (salt) accounts for about 90 percent of total sodium intake in
the United States. As Table 3 shows, most of the sodium chloride found in the
typical diet is added to food during processing.
Because salt is naturally present in only a few foods, such as celery and
milk, the reduction of dietary salt does not cause diets to be inadequate in other
nutrients. Although sodium chloride is the primary source of dietary sodium,
other forms often found in foods as food additives include monosodium
TABLE 3 Sources of Dietary Sodium Chloride
Percent of Total
Source of Salt Sodium Chloride Intake
Added to food during processing 77
Naturally occurring in foods 12
Added while eating 6
Added during cooking 5
Tap water <1
OCR for page 392
DRIs: THE ESSENTIAL GUIDE TO NUTRIENT REQUIREMENTS
392
glutamate, sodium benzoate, sodium nitrite, and sodium acid pyrophosphate.
Sodium bicarbonate and sodium citrate are found in many antacids, which are
sometimes consumed in large amounts.
Foods that are processed or canned tend to have high levels of additives
that contain sodium. Examples include luncheon meats and hot dogs, canned
vegetables, processed cheese, and potato chips. Condiments such as
Worcestershire sauce, soy sauce, and ketchup also contain substantial amounts
of sodium.
Dietary Supplements
This information was not provided at the time the DRI values for this nutrient
were set.
Bioavailability
This information was not provided at the time the DRI values for this nutrient
were set.
Dietary Interactions
There is evidence that sodium and chloride may interact with certain other
nutrients and dietary substances (see Table 4).
INADEQUATE INTAKE AND DEFICIENCY
Overall, there is little evidence of any adverse effect of low dietary sodium in-
take on serum or plasma sodium concentrations in healthy people. Chloride
loss usually accompanies sodium loss. Excess chloride depletion causes hy-
pochloremic metabolic alkalosis, a syndrome seen in individuals with signifi-
cant vomiting. In such cases, the chloride depletion is mainly due to the loss of
hydrochloric acid. However, chloride deficiency is rarely seen in healthy people
because most foods that contain sodium also provide chloride.
Special Considerations
Physical activity and temperature: Extremely vigorous physical activity per-
formed in high temperatures can potentially affect sodium chloride balance
due to the loss of sodium through sweat. The loss depends on a number of
factors, including overall diet, sodium intake, sweating rate, hydration status,
and one’s degree of acclimation to the heat. People who are accustomed to heat
exposure lose less sodium through their sweat than those unaccustomed to
high temperatures.
OCR for page 393
PART III: SODIUM AND CHLORIDE 393
TABLE 4 Potential Interactions with Other Dietary Substances
Substance Potential Interaction Notes
SUBSTANCES THAT AFFECT SODIUM AND CHLORIDE
Potassium Increased potassium intake Potassium may inhibit sodium reabsorption in the
increases urinary excretion kidneys, thereby reducing extracellular fluid and
of sodium chloride and blunts plasma volumes. This is considered to be an
the rise in blood pressure important aspect of the antihypertensive effect of
resulting from excess sodium potassium.
intake.
SODIUM AND CHLORIDE AFFECTING OTHER SUBSTANCES
Sodium: Sodium:potassium ratio is Clinical trials have shown that increased potassium
potassium typically more closely intake lowers blood pressure, and the effects of
ratio associated with blood potassium in reducing blood pressure appear to be
pressure than the intake greatest when sodium is concurrently high. Increased
of either substance alone, potassium intake also reduces the sensitivity of blood
especially in older adults. pressure changes to sodium intake.
The incidence of kidney Currently, there are not enough data to set different
stones has been shown to intake recommendations based on the
increase with an increased sodium:potassium ratio.
sodium:potassium ratio.
Diuretics: Diuretics increase urinary excretion of water, sodium, and chloride, some-
times causing low blood levels of sodium (hyponatremia) and chloride (hypo-
chloremia). Some people have experienced severe hyponatremia as a result of
taking thiazide-type diuretics. However, this appears to be due to impaired
water excretion rather than excessive sodium loss since it can be corrected
by water restriction.
Cystic fibrosis: This genetic disorder is characterized by the body’s production
of abnormally thick, viscous mucus due to the faulty membrane transport of
sodium chloride. As a result, the sodium and chloride content of sweat is very
high. Although the increased amount of sodium and chloride required by people
with cystic fibrosis is unknown, the needs are particularly high for those who
exercise and therefore lose additional sodium and chloride through sweat.
Diabetes: High blood glucose levels increase renal excretion of sodium and
water. In instances of acute hyperglycemia (e.g., diabetic ketoacidosis), low blood
OCR for page 394
DRIs: THE ESSENTIAL GUIDE TO NUTRIENT REQUIREMENTS
394
levels of sodium may occur and can generally be treated with intravenous so-
dium chloride and water along with insulin. Some hypoglycemic medications,
such as chlorpropramide, have been associated with low blood sodium levels.
In some elderly people with diabetes, hyporeninemic hypoaldosteronism may
increase renal sodium loss.
EXCESS INTAKE
The major adverse effect of increased sodium chloride intake is elevated blood
pressure, which has been shown to be an etiologically related risk factor for
cardiovascular and renal diseases. On average, blood pressure rises progres-
sively with increased sodium chloride intake. The dose-dependent rise in blood
pressure appears to occur throughout the spectrum of sodium intake. How-
ever, the relationship is nonlinear in that the blood pressure response to changes
in sodium intake is greater at sodium intakes below 2.3 g/day than above this
level. The strongest dose–response evidence comes from clinical trials that
specifically examined the effects of at least three levels of sodium intake on
blood pressure. The range of sodium intake in these studies varied from 0.23
to 34.5 g/day. Several trials included sodium intake levels close to 1.5 g/day
and 2.3 g/day.
Special Considerations
Special populations: Although blood pressure, on average, rises with increased
sodium intake, there is well-recognized heterogeneity in the blood pressure
response to changes in sodium chloride intake. Individuals with hypertension,
diabetes, and chronic kidney disease, as well as older people and African Ameri-
cans, tend to be more sensitive to the blood-pressure-raising effects of sodium
chloride intake (defined as salt sensitivity) than others. Genetic factors also
influence the blood pressure response to sodium chloride.
There is considerable evidence that salt sensitivity is modifiable. In research
studies, different techniques and quantitative criteria have been used to define
salt sensitivity. In general terms, salt sensitivity is expressed as either the reduc-
tion in blood pressure in response to a lower salt intake or the rise in blood
pressure in response to sodium loading. Salt sensitivity differs among popula-
tion subgroups and among individuals within a subgroup.
The rise in blood pressure from increased sodium chloride intake is blunted
in the setting of a diet that is high in potassium or low in fat, and rich in miner-
als. Nonetheless, a dose–response relationship between sodium intake and blood
pressure still persists. In nonhypertensive individuals, a reduced salt intake can
decrease the risk of developing hypertension (typically defined as systolic blood
pressure ≥140 mm Hg or diastolic blood pressure ≥ 90 mm Hg).
OCR for page 395
PART III: SODIUM AND CHLORIDE 395
KEY POINTS FOR SODIUM AND
CHLORIDE
Sodium and chloride are necessary to maintain extracellular
3
fluid volume and plasma osmolality. The cation sodium and the
anion chloride are normally found in most foods together as
sodium chloride (salt). About 98 percent of the sodium chloride
consumed is absorbed.
Since data were inadequate to determine EARs and thus
3
calculate RDAs for sodium and chloride, AIs were instead
developed.
The AIs for sodium are set at an intake that ensures that the
3
overall diet provides an adequate intake of other important
nutrients and also covers sodium sweat losses in unacclimated
individuals who are exposed to high temperatures or who
become physically active. The AIs for chloride are set at a level
equivalent on a molar basis to that of sodium. The UL is set
based on the impact of sodium on blood pressure.
It is well recognized that the current intake of sodium for most
3
individuals in the United States and Canada greatly exceeds
both the AI and the UL.
There is inadequate evidence to support a different upper
3
intake level of sodium intake in pregnant women from that of
nonpregnant women as a means to prevent hypertensive
disorders of pregnancy.
The UL may be even lower among people whose blood
3
pressure is most sensitive to increased sodium intake (e.g.,
older persons; African Americans; and individuals with
hypertension, diabetes, or chronic kidney disease) and who
also have an especially high incidence of heart disease related
to high blood pressure.
In contrast, people who are not accustomed to prolonged
3
strenuous physical activity in a hot environment may have
sodium needs that exceed the UL because of sodium losses
through sweat.
Sodium chloride (salt) accounts for about 90 percent of total
3
sodium intake in the United States. Most of the sodium
chloride found in the typical diet is added to food during
processing. Examples include luncheon meats and hot dogs,
canned vegetables, processed cheese, and potato chips.
Condiments such as Worcestershire sauce, soy sauce, and
ketchup also contain substantial amounts of sodium.
OCR for page 396
DRIs: THE ESSENTIAL GUIDE TO NUTRIENT REQUIREMENTS
396
There is little evidence of any adverse effect of low dietary
3
sodium intake. Chloride deficiency is rarely seen because most
foods that contain sodium also provide chloride.
Diuretics increase urinary excretion of water, sodium, and
3
chloride, sometimes causing low blood levels of sodium
(hyponatremia) and chloride (hypochloremia).
The primary adverse effect related to excessive sodium
3
chloride intake is high blood pressure, which is a risk factor for
heart disease, stroke, and kidney disease.
On average, blood pressure rises progressively with increased
3
sodium chloride intake. However, this relationship is nonlinear.
