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Health Options
Alan Titchenal |
Study finds diet can
affect kidney stonesIdeally, the words "kidney" and "stone" should never appear in the same sentence. But about 10 percent of Americans will experience a kidney stone at some time. Although the incidence has increased over the past 20 years, they are not new to the human race. They have even been found in a 7,000-year-old Egyptian mummy.
Question: What is a kidney stone?
Answer: Kidney stones are composed of various types of crystals that form in the kidneys. Of the many types of stones, the most common are formed of salt crystals that contain calcium.
Q: What causes them?
A: There is no single cause, and it is not known why some people are more susceptible. Those with a family history of stones are much more likely to get them. Certain foods seem to play a role, but only in those who are susceptible.
Q: What are the symptoms?
A: Small crystals can pass from the kidneys to the bladder and out of the body without symptoms. But if the crystal is too large, a stone can lodge in a tube of the urinary system and cause great pain, usually a sharp cramping on one side of the back at a level opposite the belly button. The pain can also be in the lower abdomen and spread to the groin area.
Q: What is the treatment?
A: Usually, the stones painfully work their way through the urinary tubes and leave the body with urine. Treatment entails drinking lots of water and taking pain medication.
If a stone is too large to pass through the tubes, it can be removed medically, most commonly through lithotripsy, which uses shock waves to break the stone into smaller pieces that can pass.
Q: Can you reduce the risk?
A: A report from the Harvard Medical School, published in today's issue of the Archives of Internal Medicine, compared dietary habits with the incidence of kidney stones during a four-year study of more than 96,000 female nurses, age 27 to 44. During the study, 1,223 women developed kidney stones that were mostly the calcium-containing types.
Women who consumed more than 1,100 milligrams of calcium daily had almost half the risk of developing stones as those who consumed less than 600 milligrams. Interestingly, no reduction in risk was associated with calcium intake from supplements.
Also, women who consumed more fluids, more animal protein, less sugar and more phytate had less risk of developing stones. (Phytate or phytic acid is found naturally in foods such as whole wheat and beans.)
Although cases must be evaluated on an individual basis, the results of this study indicate that the common practice of restricting dietary calcium in those who have had kidney stones is no longer justified.
Besides reducing the risk of kidney stones, eating more milk products, whole grains and beans, along with adequate protein and not too much sugar, can provide a variety of other health benefits as well.
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Alan Titchenal, Ph.D., C.N.S. and Joannie Dobbs, Ph.D., C.N.S. are nutritionists in the Department of Human Nutrition, Food and Animal Sciences, College of Tropical Agriculture and Human Resources, UH-Manoa. Dr. Dobbs also works with the University Health Services and prepares the nutritional analyses marked with an asterisk in this section.