Kidney stones are common, affecting as many as 15 percent of people. These stones come in different varieties, with the majority of them including a calcium component. Calcium oxalate stones are the most common type and represent 56 to 80 percent of cases in adults. Understanding what causes these types of kidney stones can help you prevent them.
How Kidney Stones Form
Crystals form in the urine all the time. They are usually small and passed painlessly. Kidney stones form when conditions allow these crystals to grow in size. In particular, excessive amounts of calcium, oxalate, phosphate, uric acid or cystine in the urine can lead to kidney stones. Substances exist normally in urine that can prevent kidney stones from developing. Magnesium, citrate, pyrophosphate and other enzymes all act in the body as a deterrent to crystals forming and attaching to the surface of kidney tubes. Having too little of these substances present in urine can trigger kidney stones.
Too Much Calcium
Too much calcium in the urine -- hypercalciuria -- can be a risk factor for kidney stones and is frequently genetically determined. Certain medications such as calcium-containing antacids, loop diuretics and glucocorticoids can increase calcium secretion into the urine. Too much vitamin D can also lead to increased calcium. Hyperparathyroidism occurs when too much parathyroid hormone is produced by the body, causing calcium to be pulled from the bones into the blood and subsequently into the urine. This helps to explain the association between kidney stones and low bone density. Kidney disease, too, can cause high calcium levels in the urine when calcium is not properly absorbed back into the bloodstream. High blood pressure and obesity have also been associated with hypercalciuria.
Too Much Oxalate
Some people are born with a genetic tendency to secrete excess oxalate into the urine. This condition, hyperoxaluria, is rare; most cases of hyperoxaluria arise from other causes. For one, diets rich in oxalate may place someone at risk for kidney stones. Oxalate-rich foods include beets, chocolate, nuts, rhubarb, spinach, strawberries, tea and wheat bran. Excessive amounts of vitamin C can also increase oxalate levels, as can inflammatory bowel disease.
Too Much Protein
High amounts of dietary protein can lead to increases in both calcium and oxalate levels in the urine. The elevated protein results in lower urine pH -- an acidic environment that makes it easier for calcium oxalate kidney stones to form. It also decreases citrate levels in the urine that help prevent kidney stones from forming. The risks of kidney stone formation can often be minimized by paying close attention to diet and good hydration. If you are concerned about kidney stones, speak with a health-care provider who can evaluate the type of stones you might have and what dietary changes would be most helpful for you.
- American Family Physician: Treatment and Prevention of Kidney Stones -- An Update
- National Kidney and Urologic Diseases Information Clearinghouse: Kidney Stones in Adults
- Canadian Medical Association Journal: Strategies for Preventing Calcium Oxalate Stones
- Sao Paulo Medical Journal: Calcium Renal Lithiasis -- Metabolic Diagnosis and Medical Treatment
- Harrison's Principles of Internal Medicine, 18th Edition