Pass the Salt

CURE, Summer 2011, Volume 10, Issue 2

Dietary modifications can improve low sodium levels caused by cancer.

The recently released Dietary Guidelines for Americans, 2010 make one thing clear: we should decrease our salt intake. For cancer patients, especially those already following a low sodium diet for heart health, the idea that they may need to increase their sodium intake can seem like a huge mental shift. Yet, certain cancers and their treatments can cause a reduction in the concentration of sodium in your body, a condition called hyponatremia.

Salt is important for maintaining blood pressure, keeping muscles and nerves working properly and regulating body fluid balance. Hyponatremia is a condition that results in an imbalance of the ratio of water to salt in body fluids outside of the cells.

The frequency of hyponatremia in cancer patients is unknown, but it is the most common electrolyte disorder in the U.S. A leading cause of the disorder is a condition called the syndrome of inappropriate antidiuretic hormone (SIADH) secretion, which occurs when high levels of the antidiuretic hormone are produced and cause the body to retain water instead of excreting it through urination. SIADH accounts for approximately 30 percent of all cases of hyponatremia and affects up to 2 percent of the entire cancer population.

“In my patients going through cancer treatment, hyponatremia is somewhat prevalent,” says Stacy Kennedy, RD, a senior clinical nutritionist at the Dana-Farber Cancer Institute in Boston.

In my patients going through cancer treatment, hyponatremia is somewhat prevalent.

Several cancers can be associated with hyponatremia, says Linda Pataki, RD, a supervisor of clinical nutrition at M.D. Anderson Cancer Center in Houston. Among them are cancers of the head and neck, thyroid, kidneys, bladder, adrenal glands and gastrointestinal system, as well as cancers of the breast, skin, brain, prostate and gynecological system and various blood cancers. The highest occurrence of SIADH is in small-cell lung cancer, where it occurs in 11 percent to 46 percent of all cases.

Side effects from surgery, radiation and chemotherapy, including diarrhea and vomiting, may also cause hyponatremia, Kennedy says. The condition can also occur with many non—cancer-related situations that involve both fluid deficiency or excess, including intense, long-duration exercise, she adds. Congestive heart failure, kidney diseases, low thyroid function, eating disorders and certain pain medications, including morphine and barbiturates, may also bring it on, Pataki says.

Symptoms of hyponatremia include minor headaches, muscle cramps, fatigue, confusion, dizziness and seizures, Pataki says. Medical attention is not required for minor symptoms unless they become chronic or extreme, she adds.

If you’re in cancer treatment, hyponatremia will be spotted in the frequent blood tests that accompany treatment, Kennedy says. Narrowing down the many possible causes, including SIADH, typically requires additional blood and urine tests.

“If we see low sodium levels, we can minimize some of the symptoms,” she says.

Hyponatremia can usually be corrected by simple dietary measures, the nutritionists say. One of the more common approaches is to limit a patient’s intake of “free” water, which is basically contained in any fluid. Replacing regular water with broth, coconut water or a sports drink will usually return sodium levels to normal, Kennedy says. Sometimes these remedies are added into intravenous fluids if a patient is not eating by mouth. Eating salty foods, such as pretzels, is another way to raise sodium levels quickly, Pataki adds. However, extra salt may not be the right approach if there is co-existent heart, liver or kidney disease, so it is important to make sure your doctor or dietitian formulates a specific plan for you.

If the sodium levels don’t change from dietary adjustments, hyponatremia can be treated medically, Pataki says. If limiting fluids does not regulate levels, antibiotics, such as Declomycin (demeclocycline) or the mood-stabilizing drug lithium, which affects the flow of sodium through the body, can be used for chronic hyponatremia. Once treatment is over, the body often returns to its normal sodium levels.