Frequently Asked Questions
January 2006: Aren’t kidney stones a result of too much calcium?
Q: I was just diagnosed with kidney stones. Aren't kidney stones a result of too much calcium? I know that milk is a good source of calcium so should I avoid dairy foods?
A: Kidney stones, one of the most painful of the urologic disorders, are not a product of modern life. Scientists have found evidence of kidney stones in a 7,000-year-old Egyptian mummy! Unfortunately, kidney stones are one of the most common disorders of the urinary tract. In 2000, patients made 2.7 million visits to health care providers, and more than 600,000 patients went to emergency rooms for kidney stone problems. Men tend to be affected more frequently than women.
A kidney stone is a hard mass developed from crystals that separate from the urine and build up on the inner surfaces of the kidney. Normally, urine contains chemicals that prevent or inhibit the crystals from forming. These inhibitors do not seem to work for everyone, however, so some people form stones. If the crystals remain tiny enough, they will travel through the urinary tract and pass out of the body in the urine without being noticed.
Doctors do not always know what causes a stone to form. While certain foods may promote stone formation in people who are susceptible, scientists do not believe that eating any specific food causes stones to form in people who are not susceptible. A person with a family history of kidney stones may be more likely to develop stones. Urinary tract infections, kidney disorders such as cystic kidney diseases, and certain metabolic disorders such as hyperparathyroidism are also linked to stone formation.
A simple and most important lifestyle change to prevent stones is to drink more liquids - water is best. Those who tend to form stones are encouraged to drink enough liquids throughout the day to produce at least 2 quarts of urine in every 24-hour period.
Individuals prone to forming calcium oxalate stones may be asked by their doctor to cut back on certain foods if their urine contains an excess of oxalate:
- beets
- chocolate
- coffee
- cola
- nuts
- rhubarb
- spinach
- strawberries
- tea
- wheat bran
People should not give up or avoid eating these foods without talking to their doctor first. In most cases, these foods can be eaten in limited amounts. Those with very acidic urine may need to eat less meat, fish and poultry as these foods increase the amount of acid in the urine.
Individuals who form calcium stones used to be told to avoid dairy products and other foods with high calcium content. However, many current studies have shown that foods high in calcium, including dairy products, may help prevent calcium stones. Researchers from Washington State University conducted a study investigating whether increasing calcium in the diet could potentially reduce the risk of kidney stones by lowering levels of urinary oxalate. The study participants had a history of at least one calcium oxalate stone. The two study diets used differed only when milk was substituted for apple juice. The diet itself was moderately high in oxalates. The milk-drinking group - with higher calcium intakes - had lower levels of urinary oxalate, which could potentially reduce the risk of kidney stones. The researchers believe that milk binds with the oxalate in a meal, rendering it unavailable for kidney stone formation.
Taking calcium in pill form, however, may increase the risk of developing stones. People with kidney stones may be told to avoid certain types of antacids that have a calcium base.
Most kidney stones pass out of the body without any intervention by a physician. Stones that cause lasting symptoms or other complications may be treated by various techniques, most of which do not involve major surgery. Also, research advances have led to a better understanding of the many factors that promote stone formation.
Massey LK, Kynast-Gales SA. Substituting milk for apple juice does not increase kidney stone risk in most normocalciuric adults who form calcium oxalate stones. J Am Dietetic Assoc, 98(3): 303-8,1998
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