I have kidney stones. Should I cut back on calcium?

Question: I have kidney stones. Should I cut back on calcium?

Answer: There is a lot of confusion around calcium and kidney stones. For years, people with calcium-containing kidney stones were advised to eat a low-calcium diet. The thinking was that calcium in foods and supplements contributed to stone formation. But today we now that isn't true. In fact, people with calcium oxalate kidney stones – the most common type – are told to meet their daily calcium requirements. We now know it's important to not restrict calcium intake.

Many studies have found that eating a calcium-rich diet is associated with a lower risk of kidney stone formation in men and women. Calcium is thought to help prevent kidney stones by binding oxalate in the intestinal tract. Oxalate is a type of salt that crystalizes with calcium in the urine to form stones; it's found in certain foods like nuts, spinach, rhubarb, parsley, tea and chocolate. By binding to oxalate in the gut, calcium reduces the amount of oxalate that gets absorbed and makes its way to the urine.

Adults, aged 19 to 50, need 1,000 milligrams of calcium each day, the equivalent of three servings of dairy or calcium-enriched beverage. (One serving is equivalent to one cup of milk or fortified beverages, ¾ cup yogurt or 1.5 ounces of cheese.) Women over 50 need 1200 milligrams of calcium each day; men's calcium requirements increase to 1200 milligrams at 70 years of age.

If you don't get all your calcium from food, take a supplement. Since calcium reduces the absorption of oxalate from foods, take your calcium supplement with, rather than apart, from meals. I recommend that you speak to your dietitian or doctor about supplementing safely.

If you have calcium oxalate kidney stones you should also limit your intake of foods high in oxalate. Although it's present in many foods, only a fraction of dietary oxalate is available for absorption. As a result, food sources don't contribute much oxalate to the urine. Studies do show, however, spinach, rhubarb, nuts, chocolate, tea, wheat bran and strawberries increase oxalate in the urine and should be avoided.

And finally – be sure to drink 12 cups of water throughout the day to help flush away substances that can cause kidney stones. On hot days, drink an additional 2 to 4 cups to make up for fluid lost through sweating.

Send dietitian Leslie Beck your questions at dietitian@globeandmail.com. He will answer select questions, which could appear in The Globe and Mail and/or on The Globe and Mail website. Your name will not be published if your question is chosen.

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