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The most recent surveys have found the average American annually drinks 10 pounds of coffee which translates into about 2.4 BILLION pounds alone. With all that consumption has come studies finding coffee--although it's a safer option to drink than soft drinks or fruit drinks--has its own sets of risks.
Among others, coffee may interfere with your body's ability to keep homocysteine and cholesterol levels in check, most likely by inhibiting the action of the vitamins folate, B12 or B6, and has been previously associated with increased risk of stroke and rheumatoid arthritis.
New research has found a new problem with coffee: People who are prone to kidney stones should limit their caffeine intake. In fact, when patients were given the caffeine equivalent to two cups of coffee, researchers found people started excreting more calcium in their urine, putting them at increased risk of forming kidney stones.
Scientists advised stone suffers limit themselves to less than two cups of coffee per day or a comparable amount of caffeine from other sources. That means two 8-ounce cups and not two enormous mugs of coffee, which can contain much more caffeine. a spike in urinary calcium increases the risk of stones because calcium is an important ingredient in kidney stones.
Previous research showed that people who do not tend to form kidney stones also excrete more calcium in their urine after consuming caffeine.
To investigate whether the same thing happens in people prone to stones, 39 people with kidney stones and nine who never had stones were asked to drink caffeine added to water after 14 hours of fasting. Researchers tested their urine two hours before and after they consumed caffeine.
After consumming 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.
Yahoo News September 3, 2004