Taking vitamin C (ascorbic acid) supplements nearly doubles the risk of developing kidney stones (RR=1.92) according to an 11 year study of almost 50,000 Swedish men. Typical vitamin C supplements in Sweden contain 1000 mg per tablet. One tablet or more per day increased risk. Those with a history of kidney stones should be especially careful of high-dose ascorbic acid.
PositiveTip: Get your vitamin C from consuming a variety of fruits and vegetables--and be kind to your kidneys.