The Medicine Cabinet: Ask the Harvard Experts
By Howard LeWine, M.D.
Q: I recently had a kidney stone. The pain was awful. Fortunately I passed it. What can I do to prevent another one?
A: It’s so important that you are thinking about avoiding another one. In about half of people who have had one, kidney stones strike again within seven years without preventive measures.
Kidney stones form when certain chemicals become concentrated enough in your urine to form crystals. The crystals grow into larger masses (stones), which may make their way through the urinary tract. If the stone gets stuck somewhere and blocks the flow of urine, it causes pain.
Most stones occur when calcium combines with one of two substances: oxalate or phosphorous. Stones can also form from uric acid, which forms as the body metabolizes protein.
To prevent kidney stones, you need to prevent the conditions that make stones more likely to form. Here are the most important steps:
Drink plenty of water. Drinking extra water dilutes the substances in urine that lead to stones. Strive to drink enough fluids to pass 2 liters of urine a day, which is roughly eight standard 8-ounce cups. It may help to include some citrus beverages, like lemonade and orange juice. The citrate in these beverages helps to block stone formation.
Get the calcium you need. Getting too little calcium in your diet can cause oxalate levels to rise and cause kidney stones. Obtain calcium from foods, not from supplements.
Reduce sodium. A high-sodium diet can trigger kidney stones because it increases the amount of calcium in your urine. A low-sodium diet is therefore recommended for the stone prone. Try to keep daily sodium intake to less than 2,300 mg.
Limit animal protein. Eating too much animal protein, such as meat, eggs and seafood, boosts the level of uric acid and could lead to kidney stones. A high-protein diet also reduces levels of citrate, the chemical in urine that helps prevent stones from forming.
Avoid stone-forming foods. Beets, chocolate, spinach and rhubarb are rich in oxalate, and colas are rich in phosphate. Depending on the type of stone you passed, limiting either oxalate or phosphate can help prevent another stone from forming.
(Howard LeWine, M.D. is an internist at Brigham and Women’s Hospital in Boston and assistant professor of medicine at Harvard Medical School.)