Kidney Stones: Myths & Facts
For: Wellness Made Easy, February 2002
Most people will never form a kidney stone. But about 10 to 12% of those in industrialized societies will suffer from nephrolithiasis, better known as kidney stones, at least once in their lives. Men are four times more likely to have the disorder than women. Stones may form and go unnoticed until they leave the kidney and pass through the ureter toward the bladder and urethra. This process, which causes an intense pain known as renal colic, is usually accompanied by nausea, vomiting, diarrhea, and possibly infection. The pain sends most people to the nearest emergency room, and they may indeed end up needing hospitalization, although stones are not generally life-threatening and may not require any kind of surgery. Half of all first-time stone formers will have a recurrence.
All kinds of waste products are filtered out of blood by the kidneys and excreted in urine. All stones are mixtures of minerals, chiefly calcium, magnesium, and phosphate, plus oxalic acid (mostly produced in the body, but also found in some foods), uric acid (an end-product of metabolism from meat), and rarely the amino acid cysteine. If these substances accumulate without enough fluid to carry them away, stones may form in susceptible people. The most common stones are almost pure sodium oxalate (the salt of oxalic acid); others are formed from a combination of calcium oxalate and calcium phosphate. First, a core has to form so that crystallization can begin. But why stones crystallize in some people but not others is not clear. Genetics has something to do with it.
The key to effective treatment is diagnosing the kind of stone you form. If you are passing a stone, you should urinate through cheesecloth or a sieve and save the stone for chemical analysis.
First stone, only stone?
Nobody who ever passed a kidney stone wants to repeat
the experience. No one piece of potentially preventive advice will
do for all stone formers, especially where diet is concerned. You'll
need the advice of a physician knowledgeable about the different
kinds of stones. Here are some pointers for avoiding a recurrence:
• Drink plenty of fluids. This has always been the mainstay of stone prevention, and can cut your risk of recurrence by up to half, even if you do nothing else. Drink eight 8-ounce glasses of fluids a day—more if you are traveling by plane or exercising, or if the weather is hot. Go easy on alcoholic and caffeinated beverages, which tend to dehydrate. Sufficient fluid keeps the urine diluted and decreases the risk of stone formation. Aim for a urine volume of two to three quarts daily, and make sure your urine is light in color (pale yellow or almost clear). You may have to measure your urine output until you can gauge how much fluid you need.
• Some find it's beneficial to eat less animal protein, though this is controversial. You need not become a vegan. But follow the semi-vegetarian diet—lots of fruits, grains, and vegetables, with small amounts of meat and fish. Your doctor may advise you to avoid foods high in oxalates, including tea, rhubarb, beets, and spinach.
• Stone formers were once told to avoid calcium, but newer research suggests that getting the recommended amounts of calcium may actually help prevent stones in some people. This is good news, because cutting out calcium can harm bones and general health. And a low calcium intake may lead to higher oxalate levels. Nevertheless, a few stone formers may reduce their chances of recurrence by cutting down on calcium. This is why it's important for your doctor to pay attention to your body chemistry.
• Keep your sodium intake low—less than 2,400 milligrams a day. A low-sodium diet can reduce calcium in the urine. Avoid fast foods, as well as canned soups and other processed foods.
• Avoid crash diets, fad diets, high-protein diets, and any other plan for quick weight loss. Some of these diets can cause a condition called ketonuria, which may increase uric acid production and thus tends to promote kidney stones. Habitual use of stimulant laxatives is also particularly bad for stone formers.
• Drugs can be used successfully. One type, called thiazides, can keep calcium in the bones and out of the urine. Allopurinal, another type, can keep uric acid from forming.
• Supplements of vitamins C and D in very high doses may increase the risk of recurrence in some people. If you take vitamins, be sure your doctor knows how much you take.
UC Berkeley Wellness Letter, March 1998
