Last year, a man in central Arkansas was rushed to the emergency room after complaining of feeling weak and achy. Doctors were shocked when they took a urine sample and found astronomic levels of calcium oxalate crystals -- a compound found in kidney stones.

But the man had no history of kidney stones or disease. Nor had he downed any antifreeze -- a liquid known for high levels of oxalates. Nonetheless, a renal biopsy confirmed that the man's kidneys had failed -- seemingly overwhelmed by the massive amounts of oxalate constantly filtering through.

The doctors diagnosed the man with nephropathy, put him on dialysis and began asking questions about his diet. Turns out, the 56-year-old had been drinking a gallon of iced black tea everyday. Tea contains relatively high amounts of oxalate. Doctors couldn't come up with with better explanation for the man's condition, and so they concluded the man's monstrous daily tea habit ultimately ruined his kidneys.

"Black tea is a rich source of oxalate, containing 50 to 100 mg per 100 ml, a level that is similar to or higher than that in many foods considered to be rich in oxalate," doctors wrote in a letter published in the New England Journal of Medicine this week. "With 16 cups of tea daily, the patient's daily consumption of oxalate was more than 1500 mg -- a level that is higher than the average American intake by a factor of approximately 3 to 10."

The man remains on dialysis, his kidneys having failed to return to normal function.

"There are reports about kidney stones related to high oxalate intake attributed to tea, but to our knowledge there are no reports of biopsy-proven nephropathy [kidney damage] associated with excessive consumption of iced tea," Dr. Alejandra Mena-Gutierrez, co-author of the letter and a researcher with the University of Arkansas for Medical Sciences, told HealthDay.

Other common dietary sources of oxalate include star fruit, black pepper, parsley, poppy seed, amaranth, spinach, chard, beets, cocoa, (most) nuts, (most) berries, beans and more.

"Two to three glasses [a day] would be considered safe if you are not eating other oxalates," Dr. Ramya Malchira, an attending nephrologist at UCLA Health, Santa Clarita, told HealthDay. But in conjunction with eating large amounts of some of the foods listed above, Malchira said, "even two or three glasses could be too much."

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