Calcium is important for bone health and other processes in the body, and health experts usually recommend ensuring enough calcium in the diet. While many take calcium supplements to ensure they get enough of the mineral, researchers are now warning that taking calcium supplements could raise the risk of developing kidney stones.
The study was led by Christopher Loftus, who is an M.D. candidate at the Cleveland Clinic Lerner College of Medicine. He is set to present the team’s findings at the American Society of Nephrology’s annual meeting next month in San Diego, although the study is not yet published in a journal.
For the study, the researchers looked at records from 2,060 patients who had a history of kidney stones. Those patients all had two CT scans within two years. 1,500 of those patients were taking calcium supplements, 414 were taking vitamin D supplements but no calcium supplements, and the rest were taking no nutritional supplements at all.
Once the researchers analyzed the data, a pattern started to form. Those taking calcium supplements seemed to develop new kidney stones at a faster rate than those taking vitamin D or no supplements.
Calcium is related to kidney stones because when there are high levels of calcium, uric acid, or oxalate, these substances can form crystals that build up in the urine. These kidney stones can then either cause pain as they pass through the urinary system, or if they grow large enough, require surgery to remove them from the kidneys. Most kidney stones contain calcium, so the supplements may be adding more calcium to the system to help the kidney stones grow faster.
Because of the relationship between calcium and kidney stones, doctors usually advise those who have a tendency to form kidney stones to reduce the amount of calcium in their diet. However, some research from the 1990s suggests that patients can lower their risk of forming new kidney stones if they include the recommended amount of calcium in their diet. The new study hopes to shed more light on the controversy.
What the current study may suggest is that calcium supplements specifically could increase the risk of forming kidney stones, and forming them faster. Getting calcium naturally from a diet rich in dairy and other foods that contain the mineral could be beneficial because those foods contain other nutrients that help reduce the chance of kidney stones.
The researchers recommend that those who are taking calcium supplements not suddenly stop. They should always follow their doctor’s advice for what is right in their particular situation. If they are taking calcium supplements because of an osteoporosis risk, for example, their doctor might decide it is beneficial for them to continue taking those supplements for their overall health. When in doubt, patients should always discuss any health supplements they are taking with their doctor.
There are other ways those who have a tendency to form kidney stones can reduce their risk. One of the main things they can do is drink plenty of fluids, with the U.S. National Institutes of Health recommending drinking two or three liters of water and other fluids daily. This helps dilute the urine, reducing the chance that calcium crystals will concentrate and form into stones. Cutting back on salt can help as well, since salt can trigger the kidneys to add more calcium to the urine, where it can form stones. Reducing the amount of meat proteins in the diet, as well as foods like nuts and spinach which contain oxalate, could reduce the kidney stone risk too. The researchers also believe that taking vitamin D supplements could help reduce the risk of kidney stones, based on their findings.