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by Dr. Sucharu Chris Prakash, MD
Q: I am a post-menopausal woman. My doctor asked me to take calcium and Vitamin D supplement. However, I had kidney stones a few years ago. Is the calcium supplement going to increase my risk of kidney stones?
A: The short answer is No. The calcium supplement should not cause kidney stones, or increase your risk of getting them again. On the contrary, calcium supplementation would be very beneficial for your bone health. But this issue requires more explanation.
The most common type of kidney stones is calcium oxalate stones. These are usually formed when the urine becomes concentrated, which leads to crystallization of calcium oxalate in the urine. The calcium and oxalate come from our diet. Foods high in oxalate include spinach, beet greens, nuts, chocolate, and strawberries. The best way to avoid kidney stones is to drink lots of water, at least six to eight glasses daily. The water dilutes the urine, reducing the risk of crystallization. You also should avoid food containing oxalate so that there will be less of it to form calcium oxalate.
Calcium itself isn’t a problem as far as kidney stones are concerned. In fact, studies have shown that the more calcium-containing foods you eat, the lower your risk of kidney stones. Why? Researchers believe that calcium from food binds with oxalate in the intestine to form calcium oxalate. The body cannot absorb the calcium oxalate from the intestine, which is then eliminated with fecal matter. This lowers the amount of calcium and oxalate the body otherwise would have to eliminate in urine, and prevents crystallization of calcium oxalate in the kidneys.
This was confirmed during a 12-year study involving 91,731 nurses between the ages of 34 and 59, none of whom had history of kidney stones. During the 12 years of the study, 864 of the nurses developed kidney stones for the first time (about one of every 1,000). The researchers found that the higher the intake of dietary calcium, the less chances the nurses had of developing stones.
The researchers also found that some nurses who took calcium supplements on empty stomach had a higher chance of getting kidney stones. The reason for this was believed to be the fact that if you take the supplements without food or at breakfast (the meal least likely to contain foods with oxalates), the calcium couldn’t bind with oxalate in the intestines, increasing chances that both will be present and available to crystallize in the urine. They theorized that taking supplements with lunch or dinner increases the chances that calcium and oxalate will bind in the intestine, reducing the risk of stone formation.
Since you have a history of kidney stones, be sure to drink lots of water and follow these dietary suggestions to reduce your risk of a recurrence:
This information is strictly an opinion of Dr Prakash, and is not intended to replace the advice of your doctor. Dr Chris Prakash is a contributing columnist, and author of eParisExtra’s “The Doctor is In” column. He is a medical oncologist at Texas Oncology Paris. He is board certified in Internal Medicine, Oncology and Hematology. He lives in Paris, TX with his wife and two children, and can be reached at 9037850031, or Sucharu.firstname.lastname@example.org