who are prone to kidney stones or who ingest large amounts of coffee
should limit their caffeine intake, according to study results.
Researchers gave a dose of caffeine equivalent to that found in
two cups of coffee to participants who had a history of kidney stones.
Following ingestion of the caffeine, the subjects showed more calcium
in their urine; this puts them at a higher risk of forming kidney
Study authors suggest people prone to stones should limit their
intake of coffee to less than two cups or 16 ounces per day. Those
that consume other forms of caffeine, like soda, should restrict
them to a comparable amount. Analysts warn that drinkers should
measure the ounces not the servings because many mugs and beverage
containers are larger than 8 ounces.
Kidney stones are comprised of different elements and a key ingredient -- calcium.
An increase in urinary calcium suggests a greater risk of developing
stones. The more calcium in urine, the more likely stones will form.
Researchers decided to examine caffeine's affect on people
prone to the problem. After 14 hours of fasting, they gave caffeinated
water to 39 high-risk participants and nine without a history of
stones. Urine was tested and evaluated two hours before and after
participants drank the water.
Results indicate that those likely to form stones showed an increase
in calcium and sodium -- key components in developing stones.
The participants with no history of kidney stones produced similar
Both groups also showed an increase of magnesium and citrate in
their urine after drinking the caffeine. Those elements are thought
to prevent stones. However, after calculating the levels of each,
researchers concluded that the levels or magnesium and citrate created
by the caffeine were not enough to combat the increased amount of
News September 3, 2004