Vitamin C, also known as ascorbic acid, is an essential nutrient for the human body. On May 21, the US website "Medscape" published an article by Dr. Sandra Fryhofer, former president of the American College of Physicians and an associate professor at Emory University School of Medicine, reminding people that long-term excessive intake of Vitamin C may cause kidney stones.
Vitamin C is a water-soluble vitamin, so even if taken in excess occasionally, it can be excreted through urine. However, this does not mean it can be supplemented indiscriminately. The Swedish Institute for Environmental Medicine and the Department of Nutritional Epidemiology conducted a study that continuously followed up on data from over 22,000 men, of whom 907 reported taking at least 1000 milligrams of Vitamin C supplements daily. During the 10-year follow-up period, 3.4% of the Vitamin C supplement users developed kidney stones, compared to 1.8% in the non-supplement group. The risk of developing kidney stones for those taking high-dose Vitamin C supplements was twice that of the general population. The highest risk of kidney stones was found in those who took 7 Vitamin C tablets (1000 mg each) per week, while this ratio did not increase in those who took multivitamins or frequently ate foods rich in Vitamin C.
Fryhofer explained that the Vitamin C absorbed by the body is excreted in the urine in the form of oxalate. Oxalate is a major component of kidney stones, and excessive excretion increases the burden on the kidneys. This is of particular concern for individuals who already have kidney stones.
Fryhofer recommends that the daily supplemental intake of Vitamin C should not exceed 1000 milligrams. If fresh vegetables and fruits are consumed daily in sufficient quantities, additional supplementation is generally not necessary. For those who need supplements due to an irregular diet, attention should be paid to the dosage. For example, a common Vitamin C effervescent tablet contains 1000 mg of Vitamin C, and only one tablet per day is needed. It is not recommended to take multiple types of vitamin supplements simultaneously. It is particularly important to note that in the summer, increased sweating can lead to reduced urination if water intake is not timely, resulting in more concentrated urine and a higher risk of stones. Therefore, when supplementing with Vitamin C in the summer, it is crucial to drink plenty of water.