New Findings about Calcium and Kidney Stones

Dietary calcium from dairy cuts risk, but supplements boost risk

By Gordon Slovut - Star Tribune Staff Writer
The Star Tribune, Thursday, April 3, 1997


It seemed obvious: Since most kidney stones contain calcium, the way to lessen the risk of developing them would be to cut down on dairy products, our main source of calcium.

That's what many doctors suggested to kidney stone patients for years. They also recommended drinking plenty of fluids to dilute the urine, making stone formation less likely and washing out existing stones before they cause obstructions.

Now some major studies challenge that standard advice.

Here's what the new studies indicate:

>>>You may decrease your risk kidney stones by increasing your intake of dairy products.

>>> Yet, you may increase your risk of developing those painful stones by taking calcium supments.

Those findings are emerging from part of the Nurses Health Study, in which scientists have been following 92,731 women, aged 34 to 59, who did not yet have a kidney stone when they enrolled.

The women filled out food diaries in 1980, 1984, 1986 and 1990. Researchers from Harvard University kept track of the women's health records and found that, over the period of the study, 864 of them developed kidney stones.

Dietary calcium

How were they different from the ones who didn't develop kidney stones?

The nurses who consumed the most dietary calcium, primarily from dairy foods such as milk, cheese and ice cream, were only 65 percent as likely to develop kidney stones as the women who consumed the least dietary calcium.

At the same time, though, the nurses who took calcium supplements had a 20 percent greater risk of developing stones than women who didn't. The amount of the supplements didn't seem to make any difference.

There have been similar findings in studies of men.

The latest findings apply only to the most common form of kidney stones, those made of calcium and oxalate, a metabolic byproduct. Another 25 to 30 percent of kidney stones are caused by treatable infections or metabolic disorders, in which calcium intake may not play a role.

The researchers cite three possibile explanations for the findings:

  • Dietary calcium somehow reduces the amount of oxalate, one of the components of kidney stones, absorbed by the body.
  • Taking calcium supplements at breakfast or between meals somehow spills too much calcium into the urine.
  • There may be some other property in dairy products that reduces the risk of stone formation.

First a few things about kidney stones: They are extremely common. An estimated 12 percent of Americans develop them at some point in their lifetime, and they seen to run in families. They are three times more common in women.

They are also extremely painful. Here's a description from a 1992 New England Journal of Medicine article about kidney stones:

"[Pain] begins suddenly and intensifies over a period of 15 to 30 minutes into a steady, unbearable pain that causes nausea and vomiting. The pain, like the stone, often passes downward from the flank [side] along a path that curves anteriorly toward the groin."

Many stones wash out with the urine without any help from doctors. Those that are less than 5 millimeters (two-tenths of an inch) in diameter usually pass through on their own. Those that are 7 millimeters (slightly more than one-quarter of of an inch) in diameter usually don't leave without help. That leaves several options, including surgery, being removed through a tube, and being pulverized with shock waves.

Drink plenty of water

Since stones are most common in summer, dehydration probably has something to do with the problem. Doctors generally advise people who have had stones or who come from families with a history of kidney stones to drink 10 to 12 glasses of water a day.

In recent years, many doctors have prescribed thiazide diuretics normally used to lower high blood pressure) to try to prevent calcium oxalate stones from forming in people who have a tendency to develop them. Research suggests that the thiazides increase the calcium deposits in the bones.

There is evidence from previous studies that a diet high in salt, sugar or meat may increase the risk for stone formation, and that a diet rich in foods containg potassium and magnesium ay decrease the risk.

The other primary findings of the Nurses Health Study of kidney stones:

  • Women who consumed the most sugar and salt had higher rates of forming kidney stones than other women.
  • Those who consumed the most potassium (foods such as potatoes and oranges) and fluid were less likely to develop kidney stones than others.
  • Meat consumption didn't seem to have any effect on risk of stones. However, the researchers say they aren't confident of that finding because of some inadequacies in the 1980 questionnaire.

What should women make of it?

Not, necessarily, that they should stop taking calcium supplements,the researchers say. Because other consequences of not getting enough calcium (such as osteoporosis) can be severe, Women who don't get enough calcium in their diet ought to consider taking their supplements with lunch or dinner, not with breakfast or between meals (as many of the nurses did), the researchers said.

An editorial writer in Annals of Internal Medicine, where the kidney stone report appears, said the study reinforces the trend to avoid low-calcium diets.

Kidney Stone


Star Tribune - Briefs

Not practicing what they preach

Scripps Howard News Service

Many hospitals are failing to match their menus to their medicine. They're still serving up cholesterol-rich, hi-fat meals while urging patients to adopt healthful eating habits at home, a doctors group said this week.

The Physicians Committee for Responsible Medicine found that nearly a third of the 30 hospitals it surveyed reported that their best available low-fat meal included such items as roast beef, chicken and seafood Newburg.

The committee suggests offering patients low-fat, plant-based - as in - vegetarian meals, which many studies have found can help prevent heart disease, cancer, diabetes and other illnesses.

The study supports results of a 57-hospital study published in November by New York researchers who found that only 20 percent of hospitals hit the goal of keeping cholesterol intake to 3OO milligrams a day or less, and just over half were able to keep fat to 10 percent or less of the daily calorie intake.


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