Taking Calcium Supplements? Want To Avoid Kidney Stones?

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Taking Calcium Supplements? Want To Avoid Kidney Stones?

JoAnn Guest

Apr 05, 2007 14:41 PDT

 

 

A study published in the New England Journal of Medicine, April 1,

1997, has important implications for women who take calcium

supplements for

the prevention of osteoporosis, a common condition affecting 20

million women that results in thinning of bones and leads to

fractures of the hips and spine.

 

http://www.medicinenet.com/script/main/art.asp?articlekey=1887

 

Kidney stones also are a common condition in which stones form in

the kidney and result in pain, bleeding into the urine, and blockage

of the ureters, the tubes that conduct urine from the kidney to the

bladder.

 

The major components of the most common type of kidney stone are

calcium

and oxalate both of which come primarily from the diet, that is, the

food we eat.

 

The study was a large, epidemiological study of 91,731 nurses who

had

never had kidney stones and were between the ages of 34 and 59 at

the

beginning of the study in 1980. The nurses were followed with

questionnaires for 12 years. The questionnaires asked specifically

about

dietary habits, calcium supplements, and kidney stones. The dietary

intake of calcium also was estimated from the dietary habits.

 

During the 12 years of the study, 864 nurses developed kidney stones

for

the first time. Each year, one of every 1,000 nurses developed

stones

(for an incidence of 0.1% per year). There was a strong association

between higher dietary calcium intake and stones, that is, the

greater

the intake of calcium, the fewer the nurses developing stones.

Nurses

taking the highest amount of dietary calcium were half as likely to

develop stones as women taking the lowest amount of dietary calcium.

 

Among nurses taking calcium supplements (in addition to their

dietary

calcium) the risk of developing stones was greater than among nurses

not

taking calcium supplements. Specifically, nurses taking supplemental

calcium were 20% more likely to develop stones as women not taking

supplemental calcium.

 

The relationship between dietary calcium and kidney stones is

complex.

It is known-and this study confirms--that increasing amounts of

dietary

calcium are associated with fewer kidney stones. It is believed that

this occurs because the increased amounts of calcium from food binds

to

oxalate from food in the intestine, and the complex of calcium and

oxalate cannot be absorbed into the body. This reduces the amount of

calcium and oxalate that needs to be eliminated from the body in the

urine and prevents the formation of calcium/oxalate stones in the

kidneys. In fact, calcium supplements have been used successfully to

decrease the elimination of oxalate in the urine.

 

Why then, were calcium supplements associated with more kidney

stones in

the nurses? The study's investigators hypothesize that the reason is

the

time at which the nurses took the calcium supplements. The calcium

and

oxalate in food can bind to each other only if they are present at

the

same time in the intestine. If calcium supplements are taken with

meals

containing the most oxalate, everything is fine, and the calcium and

oxalate bind. If calcium supplements are taken with meals that

contain

little or no oxalate, the oxalate doesn't bind to calcium, and the

oxalate is absorbed from the intestine and then eliminated in the

urine.

Furthermore, if calcium supplements are not taken with food, more

calcium is absorbed and eliminated in urine. (This would increase

the

risk for developing stones.) It turns out that 57% of the nurses in

the

study taking supplements were not taking them with meals, and 24%

were

taking the supplements only with breakfast, the meal least likely to

contain oxalate. Thus, more than three-quarters of the nurses taking

calcium supplements may have been absorbing and eliminating more

calcium

in their urine or were not gaining the benefit of the binding of

calcium

and oxalate in the intestine.

 

The study's investigators conclude that a high intake of dietary

calcium

reduces the risk of kidney stones but supplemental calcium increases

the

risk. They suggest that the risk of kidney stones among women taking

supplemental calcium might be reduced by consuming the supplements

with

meals, particularly meals which contain the most oxalate-lunch and

dinner. Although it would be best to have the author's suggestion

verified by a scientific study in which stone formation is compared

between women taking calcium supplements " correctly " and women

taking

calcium supplements " incorrectly, " such a study is unlikely to be

done,

and if it is done, it will take many years before the results are

known.

Therefore, women now taking supplemental calcium must decide how to

take

their supplements based on the scientific data that exist and the

suggestions that have been made.

 

 

JoAnn Guest

mrsjo-

www.geocities.com/mrsjoguest/