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Dr. Roach: Sodium and kidney stone risk linked

Keith Roach
To Your Health

Dear Dr. Roach: You recently wrote that sodium intake increases kidney stone risk. I thought kidneys filtered out serum calcium, meaning calcium intake causes calcium oxalate stones. As someone who suffered from hyperparathyroidism and kidney stones, it is my understanding that excess serum calcium causes stones. Nowhere in my research into this disease, nor in discussions with my parathyroid expert surgeon, did I ever hear of salt contributing to stone formation. I would greatly appreciate a clarification as to salt’s role in the formation of calcium stones, as I do love my salt.

— A.G.

Dear A.G.: I am always happy to discuss physiology.

A high sodium diet requires the kidney to excrete the excess sodium. The sodium transporters across the membrane in the kidney require calcium to be excreted as well. A high sodium diet increases calcium loss in the urine by six-fold in laboratory studies. The high amount of resultant calcium in the urine will lead to stone formation in people genetically predisposed to do so.

Even in people who do not form stones, a high sodium diet will cause the body to excrete excess calcium, potentially leading to osteoporosis. Even though blood pressure is the major argument against a high sodium diet, kidney stones and bone health are other reasons not to take in excessive sodium.

Dr. Keith Roach

Dear Dr. Roach: Why would a person lose his or her voice after carotid surgery? It’s been over three months.

Anon.

Dear Anon.: Some changes to the voice are common after any surgery. This is due to the placement of the endotracheal tube, which passes through the vocal cords. However, that usually goes away in a few hours, or a day or two. Three months makes me worry about damage to the recurrent laryngeal nerve, which provides the nerve supply to the vocal cords. Damage to the nerve can cause variable symptoms, from hoarseness to a complete loss of voice.

Damage to the recurrent laryngeal nerve is fairly common in carotid surgery. One study found that 18 percent of people undergoing carotid surgery had some damage to vocal-cord function — some had no symptoms, and the remainder recovered, except for 1 patient out of 50, who had permanent damage.

Damage to the vocal cord can be diagnosed by an ENT doctor via laryngoscopy or videostroboscopy. It’s important to make a diagnosis, since there are other causes. Although the timing of the carotid surgery seems to make it definitive as the cause, hoarseness and vocal loss are important signs of neck tumors.

Readers may email questions to ToYourGoodHealth@med.cornell.edu.