Calcium and kidney stones

Philip J. Goscienski, M.D.

June 2007

Old myths live on and on. A newspaper article not long ago warned that taking too much calcium causes kidney stones. That simply is not true. Taking too little calcium causes kidney stones.

Stone Agers took in about 4 times as much calcium as the average American (about 1700 milligrams per day versus about 440). Almost all of it came from plant foods, a much better source than dairy products. It probably never occurred to anyone 50,000 years ago to try to milk a wild animal and they were the healthier for it.

Only about 20 percent of the calcium in our diet gets absorbed into the bloodstream. Some of the rest stays in the intestines and binds with oxalate, a chemical that is present in many foods, so that the calcium-oxalate compound passes out of the body. If there's not enough calcium to tie up that oxalate it gets absorbed and goes through the kidneys where it can then combine with other calcium molecules to form a stone.

Calcium oxalate is responsible for most (about 70 percent) of kidney stones but the good news is that this condition is largely preventable. Drinking adequate fluids is one of the most important factors and one that is easy to manage. Forget the mathematical formulas that are based on body weight. There is so much variation in our individual lifestyle and environment that no calculation fits everyone. Simply make sure that you drink enough fluid to keep your urine pale yellow. If it's dark with a pungent odor it will increase your risk of developing kidney stones.

A diet that is high in fruits and vegetables is a big help, especially for those persons who have a personal or family history of kidney stones. Plant foods contain lots of potassium and very little sodium, two very important factors in reducing stone formation. Contrary to the popular image of the Stone Age, humans lived mostly on plant foods for the million or so years before we figured out how to bring down large animals. A diet that is high in animal protein not only shifts the acid-base balance in the wrong direction, it favors the development of other kinds of kidney stones as well as those that are formed from calcium oxalate.

There are other reasons for not following the low-calcium diet advice. Most of us don't get enough calcium, putting many at risk of osteoporosis later in life. An inadequate intake of calcium also contributes to high blood pressure.

There are some foods that are naturally high in oxalate and persons who have had a kidney stone should limit their intake of these or avoid them completely. Some happen to be plant foods but they aren't particular favorites anyway: rhubarb, spinach, beets (the root and greens), Swiss chard, okra and collard greens. The list includes some we enjoy: chocolate, kidney beans, refried beans and tea. Have them in small amounts and only occasionally.

For the one reader in 10 who is destined to have a kidney stone, getting enough calcium and other nutrients through a variety of vegetables and fruits is worth the effort. Just ask the person who has had one!

Philip J. Goscienski, M.D. is the author of Health Secrets of the Stone Age, Better Life Publishers 2005. Contact him at