Salt Sensitivity
Some people may be more sensitive to the effects of salt on
blood pressure.
Dietary salt restriction has been reported to lower blood pressure
significantly in about half of those with hypertension and a third of those with normal blood pressure.
Salt sensitivity may be more common in obese and insulin-
resistant individuals, and in African American, elderly, and female hypertensive patients. Organ Damage
High salt intake may contribute to organ damage in ways that are
independent of its effects on bl
ood pressure. Increased salt intake
may be associated with pathological changes in the structure and function of large elastic arteries that are independent of changes in blood pressure.
Toxicity (Hypernatremia)
Abnormally high blood sodium conc
entrations (hypernatremia)
generally develop from excess water loss accompanied by an impaired thirst mechanism or lack of access to water.
Signs and symptoms of hypernatremia in the presence of fluid
loss include dizziness, fainting, low blood pressure, and diminished urine production.
Hypernatremia may be caused by excessive sodium intake (for
example, the ingestion of large amounts of seawater or intravenous infusion of concentrated saline solution).
Salt tablets do not stimulate thirst as much as salty foods do.
Overzealous use of salt tablets has been associated with hypernatremia, especially when fluid intakes have been relatively low.
Ingestion of large amounts of salt may lead to nausea, vomiting,
diarrhea, and abdominal cramps. Severe hypernatremia may result in
edema (swelling), hypertension, rapid heart rate, difficulty breathing, convulsions, coma, and death.
Athlete Considerations: Hyponatremia
Sodium is the electrolyte priority for the aerobic endurance
athlete.
Loss in sweat
: 230 to 1,700 milligrams per liter.
37
With an intake of 4,000 milligra
ms and an absorption efficiency
over 90%, about 3,600 milligrams of sodium are absorbed daily.
With a loss of about 1,000 milligra
ms per liter of sweat, it is easy
to sweat out about 4,000 milligrams of sodium with a gallon (4 quarts, 4 liters) of sweat. This could overwhelm your daily intake.
Blood sodium levels may drop. A
low concentration of sodium
in the blood is associated with weakness, fatigue, seizures, and occasionally death.
In temperate weather conditions, this may take 4 or 5 hours. In
high-heat conditions, sodium depletion can occur in just a couple of hours.
In many athletes, low sodium problems first occur in target long-
distance events—because these events
may last 50% longer than the
longest previous training session.
Many athletes, observing general healthy-diet guidelines, watch
their sodium intake and keep it low. This is not necessarily a good strategy for most endurance athletes.
Hyponatremia is well-recognized as a problem in athletes
competing in aerobic endurance exer
cise events such as marathons,
century bicycle rides, and Ironman-length triathlons. Longer ultra-events place athletes at even higher risk.
37 Biolab Medical Unit (UK) reference ranges. http://www.biolab.co.uk/repswe.html. Accessed 10-28-2004.
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