You are viewing this article in the AnnArbor.com archives. For the latest breaking news and updates in Ann Arbor and the surrounding area, see MLive.com/ann-arbor
Posted on Sat, Oct 29, 2011 : 5 a.m.

Can I prevent kidney stones?

By Ask Dr. K

Harvard Medical School Adviser by the Faculty of Harvard Medical School

Q:

I'm a 30-year-old man. Like many of my friends, I've gained weight since college. I read that being overweight can lead to kidney stones. A friend who just had kidney stones told me that passing them was incredibly painful. I'd like to lose weight, but until I succeed, is there anything I can do to prevent kidney stones?

A:

When it comes to illnesses, there are worse things than kidney stones. But when it comes to pain, the passing of a stone is near the top of the list. Kidney stones are excruciatingly painful when they travel through the ureters, the tubes that connect the kidneys to the bladder.

As you may know, kidney stones are hard, chemical and mineral deposits that form inside the kidneys. Tiny stones may pass out of the body in urine without causing any discomfort. In fact, about nine out of 10 kidney stones will pass on their own within three to six weeks after forming.

However, a deposit can grow to be the size of a pea, a marble or even larger. These large stones may irritate the narrow ureter, causing pain and bleeding. Stones greater than one-fifth of an inch may have difficulty passing through the narrow ureter. Even worse, a stone may become lodged in the ureter, blocking the passage of urine and threatening to damage the kidney itself.

The number of Americans suffering from kidney stones is increasing, perhaps because of the increasing prevalence of obesity. In general, stones strike men twice as often as women.

A Harvard study of nearly 46,000 men (ages 40 to 75) found that high body mass indexes and large waist circumferences are both linked to an increased risk of kidney stones. And research from Europe and Asia shows that overweight people dump excess amounts of calcium and other chemicals into their urine, where the chemicals form stones.

Each year about a million Americans undergo treatment for kidney stones. One option is lithotripsy, a treatment that uses a series of ultrasonic shock waves to break up large stones into smaller ones that can be passed out of the body when you urinate.

But your focus on prevention is a good one because once you get kidney stones, the chance of getting them again is high. Much of the prevention advice is aimed at fending off a recurrence, but it may also help you to avoid kidney stones in the first place. Here are a few pointers:

-- Keep your fluid intake up. Kidney stones form when certain chemicals and minerals concentrate in the urine and form crystals. Drink plenty of fluids -- water is the safest bet. This will increase the amount of water in your urine, so those mineral concentrations don't get too high.

-- Eat calcium-rich foods. Calcium is a major component in about 85 percent of kidney stones, so it seems logical to avoid calcium in your diet, not seek it out. But most stones are composed of calcium combined with a substance called oxalate. If there is plenty of calcium in your diet, the calcium binds to oxalate in your intestines, keeping oxalate out of your bloodstream -- and urine. Less oxalate in the urine means fewer opportunities for calcium oxalate to form -- and fewer kidney stones. Calcium-rich foods include nonfat dairy products, leafy green vegetables and some varieties of fish, such as salmon.

-- Reconsider calcium supplements. This recommendation pertains mostly to women, who are often encouraged to take daily calcium supplements to promote bone strength, but the advice applies to men as well. Results from the Harvard-based Nurses' Health Study showed that postmenopausal women who took calcium supplements were 20 percent more likely to develop kidney stones than women who didn't.

-- Moderate your sodium intake. Low-sodium diets decrease urinary excretion of calcium.

-- Moderate your protein intake. Protein can increase calcium and oxalate excretion, raising the probability of stone formation. High-protein diets may also reduce the levels of stone-inhibiting substances in the urine.

-- Moderate your oxalate intake. Calcium intake and other dietary factors seem to be more important than oxalate intake in forming kidney stones, but high oxalate intake can occasionally be a factor. Oxalate-rich foods include beets, chocolate, spinach, rhubarb and most nuts.

A number of risk factors contribute to kidney stone formation, including certain medical conditions. While the guidelines above are a good way to start reducing your risk of stones, your doctor may have good advice about personal prevention strategies for you.

As your friend can tell you, it's far better to prevent kidney stones than to spend a night in terrible pain with a stone that just doesn't want to pass.

(Submit questions to harvard_adviser@hms.harvard.edu.)

COPYRIGHT 2011 THE PRESIDENT AND FELLOWS OF HARVARD COLLEGE.

DEVELOPED BY HARVARD HEALTH PUBLICATIONS, WWW.HEALTH.HARVARD.EDU.

DISTRIBUTED BY UNIVERSAL UCLICK FOR UFS