Melissa Conrad Stöppler, MD, is a U.S. board-certified Anatomic Pathologist with subspecialty training in the fields of Experimental and Molecular Pathology. Dr. Stöppler's educational background includes a BA with Highest Distinction from the University of Virginia and an MD from the University of North Carolina. She completed residency training in Anatomic Pathology at Georgetown University followed by subspecialty fellowship training in molecular diagnostics and experimental pathology.
Dr. Shiel received a Bachelor of Science degree with honors from the University of Notre Dame. There he was involved in research in radiation biology and received the Huisking Scholarship. After graduating from St. Louis University School of Medicine, he completed his Internal Medicine residency and Rheumatology fellowship at the University of California, Irvine. He is board-certified in Internal Medicine and Rheumatology.
Author: Richard Weil, MEd, CDE
Medical Editor: William C. Shiel Jr., MD, FACP, FACR
Viewer Question: My trainer is always telling me to stay hydrated. How much water should I drink when exercising? What will happen if I drink too much?
Fitness Expert's Response: The National Athletic Trainers' Association recommends the following hydration guidelines for exercise:
Two to three hours pre-exercise: 17 to 20 fluid ounces of water or sports drink.
Ten to 20 minutes pre-exercise: 7 to 10 ounces of water or sports drink.
During exercise: Fluid replacement should approximate sweat and urine losses and at least maintain hydration at less than 2% body weight reduction. This generally requires 7 to 10 ounces of water or sports drink every 10 to 20 minutes. Include carbohydrates in the beverage if the exercise is intense or lasts more then 45-50 minutes. Water alone will suffice, and save calories, if the exercise is moderate or less than 45-50 minutes.
Post-exercise: Athletes should weigh themselves nude before and after workouts to learn how much weight is lost from sweat (water and salt) and then ingest fluid equal to 150% of the weight loss, ideally within two hours, and no more than four to six hours after the event. Including sodium in the drink allows fluid volume to be better conserved and increases the drive to drink, and carbohydrate in the drink will improve the rate of intestinal absorption of the fluid as well as replenish glycogen stores in the muscles and liver.
Hyponatremia refers to a lower-than-normal level of sodium in the blood.
Sodium is essential for many body functions including the maintenance of fluid
balance, regulation of blood pressure, and normal function of the nervous
system. Hyponatremia has sometimes been referred to as "water intoxication,"
especially when it is due to the consumption of excess water, for example during
strenuous exercise, without adequate replacement of sodium.
Sodium is the major positively charged ion (cation) in the fluid outside of
cells of the body. The chemical notation for sodium is Na. When combined with
chloride (Cl), the
resulting substance is table salt (NaCl).
The normal blood sodium level is 135 - 145 milliEquivalents/liter (mEq/L), or
in international units, 135 - 145 millimoles/liter (mmol/L). Results may vary
slightly among different laboratories.
What causes hyponatremia (low blood sodium)?
A low sodium level in the blood may result from excess
water or fluid in the body, diluting the normal amount of sodium so that the
concentration appears low. This type of hyponatremia can be the result of
chronic conditions such as kidney failure (when excess fluid cannot be
efficiently excreted) and congestive heart failure, in which excess fluid
accumulates in the body. SIADH (syndrome of inappropriate anti-diuretic hormone)
is a disease whereby the body produces too much anti-diuretic hormone (ADH), resulting in retention of water in the body.
Consuming excess water, for example during strenuous exercise, without adequate
replacement of sodium, can also result in hyponatremia.
Hyponatremia can also result when sodium is lost from the body or when both
sodium and fluid are lost from the body, for example, during prolonged
sweating and severe
vomiting or diarrhea.
Congestive heart failure (CHF) is a condition in which the heart's function as a pump is inadequate to meet the body's needs. A poor blood supply resulting from congestive heart failure may cause the body's organ systems to fail, leading to a weakened heart muscle and fluid accumulation in the lungs and body tissue. There are many diseases that can impair pumping efficiency and symptoms of congestive heart failure including fatigue, diminished exercise capacity, shortness of breath, and swelling. Treatments include lifestyle modifications, medications, heart transplant, and therapy.
Kidney failure can occur from an acute event or a chronic condition or disease. Prerenal kidney failure is caused by blood loss, dehydration, medication. Some of the renal causes of kidney failure are from sepsis, medications, rhabdomyolysis, multiple myeloma, and acute glomerulonephritis. Post renal causes of kidney failure include bladder obstruction, prostate problems, tumors, or kidney stones. Treatment options included diet, medications, or dialysis.
Diarrhea is a change is the frequency and looseness of bowel movements. Cramping, abdominal pain, and the sensation of rectal urgency are all symptoms of diarrhea. Absorbents and anti-motility medications are used to treat diarrhea.
Hypothyroidism is any state in which thyroid hormone production is below normal. Normally, the
rate of thyroid hormone production is controlled by the brain at the pituitary.
Hypothyroidism is a very common condition and the symptoms of hypothyroidism are
often subtle.
Dehydration is the excessive loss of body water. There are a number of causes of dehydration including heat exposure, prolonged vigorous exercise, and some diseases of the gastrointestinal tract. The best way to treat dehydration is to prevent it from occurring.
Cirrhosis of the liver refers to a disease in which normal liver cells are replaced by scar tissue caused by alcohol and viral hepatitis B and C. This disease leads to abnormalities in the liver's ability to handle toxins and blood flow, causing internal bleeding, kidney failure, mental confusion, coma, body fluid accumulation, and frequent infections. Symptoms include yellowing of the skin, itching, and fatigue.
Nausea is an uneasiness of the stomach that often precedes vomiting. Nausea and vomiting are not diseases, but they are symptoms of many conditions. The causes of vomiting differ according to age, and treatment depends upon the cause of nausea and vomiting.
Heart failure is caused by many conditions including coronary artery disease, heart attack, cardiomyopathy, and conditions that overwork the heart. Symptoms of heart failure include congested lungs, fluid and water retention, dizziness, fatigue and weakness, and rapid or irregular heartbeats.
Congestive heart failure (CHF) is a condition in which the heart's function as a pump is inadequate to meet the body's needs.
Many disease processes can impair the pumping efficiency of the heart to cause
congestive heart failure.
The symptoms of congestive heart failure vary, but can include fatigue, diminished exercise capacity, shortness of breath, and swelling.
The diagnosis of congestive heart failure is based on knowledge of the
individual's medical history, a careful physical examination, and selected laboratory tests.
The treatment of congestive heart failure can include lifestyle modifications, addressing potentially reversible factors, medications, heart transplant, and mechanical therapies.
The course of congestive heart failure in any given patient is extremely variable.
