New research suggests people who are prone to kidney stones should limit their caffeine intake.
The study author, Dr. Linda K. Massey of Washington State University, says stone sufferers should limit themselves to less than two cups of coffee per day or a comparable amount of caffeine from other sources.
People with a history of kidney stones tend to excrete more calcium in their urine after an intake of caffeine equivalent to that found in two cups of coffee.
Dr. Massey explained that a spike in urinary calcium increases the risk of stones because calcium is a major ingredient of kidney stones.
Previous research has shown that people who do not tend to form kidney stones also excrete more calcium in their urine after consuming caffeine, reports Xinhua.
To investigate whether the same thing happens in people prone to stones, Massey and Dr. Roger A. L. Sutton at the University of British Columbia in Vancouver, asked 39 people with kidney stones and nine who never had stones to drink caffeine added to water after 14 hours of fasting. The researchers tested their urine 2 hours before and after they consumed caffeine.
As the investigators report in the Journal of Urology, after caffeine, the stone-formers showed an increase in calcium, sodium, magnesium and citrate in their urine. The same pattern also occurred in the people with no history of kidney stones.
In an interview, Massey explained that more calcium and sodium in urine likely increases the risk of kidney stones, while increases in magnesium and citrate appear to protect people from kidney stones.
However, after plugging these changes into a formula that predicts kidney stone risk, Massey said, "The increase in magnesium and citrate did not offset the increase in calcium.", informs Reuters.
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