On Nutrition: Calcium and kidney stones

Rene from Racine, Wisconsin, writes: "I am hoping you can help me understand calcium supplements and the likelihood of kidney stones. For the first time in my 61 years, I had a kidney stone. I also have been diagnosed with osteopenia (lower than normal bone mass). I would like to take a calcium citrate supplement along with MK7 (a form of vitamin K) but read that citrate may increase stone formation. Can you advise and help clear up my confusion on calcium supplements for someone prone to kidney stones and osteopenia or recommend a reliable publication that I could understand? Thank you in advance."

Nice to hear from you, Rene. I enjoyed your nice city back in 2016 while on a book tour. Your question is a good one.

To begin, the two most popular types of calcium supplements are calcium carbonate and calcium citrate. Calcium citrate's absorption into the body does not rely as much on the release of stomach acid (that occurs after a meal) as does calcium carbonate. That means we can conveniently take calcium citrate supplements with or without meals.

Besides being well absorbed, there is also good evidence that calcium citrate supplements may prevent bone loss in older women. In fact, citrate is a major component of healthy bone.

Regarding calcium citrate and kidney stones, you might check out a 2019 review article by endocrinology professor Andrea Palermo of Bio-Medico University, Italy, and her colleagues in Reviews in Endocrine and Metabolic Disorders. These experts cite evidence that calcium citrate supplements have a lower risk for kidney stones than supplements made with calcium carbonate.

And while we still don't have all the answers, it is interesting that the use of citrate salts is a widely used treatment for kidney stones. We also need to remember other strategies to lower our risk for this painful condition: Drink plenty of fluids, cut back on salt and avoid caveman portions of meat.

Lastly, don't forget that the safest and most efficient way to get adequate calcium is from our food. While supplements are a good way to get what our diets don't contain, they may come with side effects.

You didn't ask, but here are some other nice-to-knows about calcium supplements:

From your 51st birthday onward, women need 1,200 milligrams of calcium a day from food and supplements combined. Start checking the Nutrition Facts label for calcium content on your favorite foods to see if you need to add a supplement.

If you do take a supplement, your body can absorb no more than 500 milligrams at a time. That means you might need to take more than one dose a day.