Gettysburg Medical News
The Clinical View
by P.E. Hoffsten, M.D.
23 January 2002

LOW CALCIUM DIETS ARE BAD

     Kidney stones are one of the very common problems in a medical practice.  Estimates are that 1 person in 10 will develop a kidney stone during their lifetime.  Unfortunately of those that get one stone, half will get another one.  Of those that get two stones, two-thirds will have more than that.  So they tend to be recurrent.  Anyone who ever had a kidney stone or seen someone with a kidney stone, can testify to the devastating pain that comes with these events.

      Most kidney stones are made of calcium.  In the past and for many years, a standard recommendation for people that have kidney stones is to get on a low calcium diet.  The theory would be that if the person has less calcium in their diet, they would also have less calcium in their urine and kidney stones would be less likely to happen. This column is about the invalidity of this idea.

       The fact is that most kidney stones come not from too much calcium being taken in but rather from too much calcium leaking out of the kidney into the urine.  People who have kidney stones most commonly have a genetic defect that allows calcium in the blood to leak into the urine. As the kidney concentrates the waste products to excrete them in a small amount of volume, the calcium becomes too concentrated and can form kidney stones.  The fact is that decreasing the amount of calcium that a person takes in has little or no impact on how much the kidney leaks.

       One of the basic rules of life is, “When what you are doing doesn’t work, do anything else.  But don’t keep doing what you are doing because you have already shown that that doesn’t work.”  It has been shown over years that low calcium diets don’t work to prevent kidney stones, and thus new methods of treatment and prevention of kidney stones were sought.

       A recent study in the New England Journal of Medicine (a medical journal for healthcare professionals) made a comparison between low calcium diets and a diet that was low in salt and animal protein.  It was found that the individuals on the low calcium diet had twice as many kidney stones as the group of people using the low salt, low animal protein diet.  While I don’t think that I am going to sell a low protein diet to South Dakota, the idea that a low salt diet will be a help has much wider application and in my opinion is probably the more effective of the two considerations.  All of the salt that a person eats comes out in the urine.  The more salt you eat, the more salt there is in the urine.  The more salt there is in the urine, the less room there is for the calcium that is already there from the leaky kidney.  Therefore, high salt diets are probably the most significant contributor to kidney stones.

       Notice how wonderful this is.  A low salt diet costs less.  There is no medicine to take. There no side effects and you have fewer kidney stones.  What more could you ask for?

       One additional consideration regarding the low calcium diet is important.  If the kidney has a leak all the time, calcium is being slowly lost from the body.  If the person remains on a low calcium diet, they don’t replace that slow kidney loss.  It has already been shown that later in life, individuals with the calcium leak problem develop osteoporosis and a predisposition to hip and back fractures.

       In summary, low calcium diets don’t work and probably contribute to hip and vertebral fractures.  Low salt diets do work to cut down the incidence of kidney stones and also prevent high blood pressure and heart failure.  Low calcium diets are bad.  Low salt diets are good.