Calcium May Help Prevent Kidney Stones
But new research at University of Wisconsin School of Medicine and Public Health shows that calcium supplements may help prevent kidney stones.
That's good news for kidney-stone sufferers who like to eat. It means they can have that spinach and beet salad, followed by strawberry-rhubarb pie, as long as they take a calcium supplement with dinner. It would be even better to squeeze a bit of lemon juice on that salad and have a glass of skim milk with the pie.
It used to be that people who had suffered through the miseries of kidney stones were told to avoid high-oxalate foods, which include such healthful items as spinach, beets, strawberries, nuts, soybeans and black and green tea. They may have also been told to avoid calcium. The reason was that about 80 percent of kidney stones are made up of calcium oxalate.
But it turns out that kidney stones – which are now on the rise in children and women – can't be blamed solely on foods, said Kristina Penniston, a registered dietician with the UW urology department. Penniston studies how to modify diets to prevent kidney stones.
"We used to think they were caused by high-oxalate foods," she said. "But, unfortunately, the rise in kidney stones isn’t because Americans are eating too much fresh spinach."
Instead, urology experts blame obesity, too much sodium, and too little fluids.
Then, a few years ago, a Harvard University study showed the surprising result: Many kidney-stone sufferers actually had low levels of calcium in their bloodstream.
"That turned everything on its head, because we used to tell people to avoid foods high in calcium and oxalate," Penniston says.
A newer theory, Penniston says, is that some stone-formers lack enough calcium to bind up the oxalate in the GI tract, allowing it into the kidneys, where it can form stones.
She, UW Health chair of urology Stephen Nakada, MD, and colleagues tested this theory by giving calcium-citrate supplements to people who tend to form kidney stones. A second group ate calcium-rich foods, such as dairy products.
Members of both groups had a significant drop in the level of oxalate in their urine, a sign they may be less likely to form stones. The important thing is to take the calcium with food so it can do its binding job.
The research team presented its findings at the American Urological Association meeting in May, and will soon publish a paper on their results.
Much of Penniston's research with Nakada has focused on dietary changes that can prevent stone formation. A few years ago, they published a study showing that lemonade could be used to prevent kidney stones, because it increases citric acid, which is known to inhibit stone formation.
Since then, they've found even better kitchen remedies. In a study published in Endourology in March, they compared the citric-acid content of 21 types of citrus juices and juice concentrates. They found that fresh or concentrated lemon and lime juices were the best sources of citric acid, with concentrations about 10 times higher than those found in lemonade.
Penniston recommends squeezing some fresh lemon or lime juice into water: it's lower in calories than lemonade and much higher in citric acid.
Her next research will look at whether nutritional supplements have an effect on kidney stone formation.
The two have also found that people with kidney stones, especially women, experience a lower health-related quality of life. But the good news from Wisconsin's urology department is that people can actually do some simple things with their diets to prevent one of the most painful afflictions from coming back.
"Men say that kidney stones are the worst pain they've even suffered," Penniston says. "Women say that it's not quite as bad as childbirth, but at least with childbirth, you know you're pregnant. You never know when you're going to develop a kidney stone."
Date Published: 11/20/2008