My mother has advised me to follow her pattern of taking three 500-milligram tablets of vitamin C each day, which she does to avoid a recurrence of breast cancer. Do you think that this is a good idea?
Supplements containing more than 400 mg of vitamin C a day only serve to enrich the vitamin C content of the toilet bowl. The body just excretes it. More importantly, federal research shows that daily doses of 1000 mg or more increases the risk of kidney stones by raising the urinary content of urate and oxalate, major components of the most common types of kidney stones.
Vitamin C supplements have been suggested as a way to protect against the highly reactive free radicals that are regularly formed during the course of normal body metabolism and are thought to promote artherosclerosis (hardening of the arteries) and cancer. It's true that free radicals can be inactivated by antioxidants like vitamin C, but at this time there is no scientific data to show that vitamin C supplements prevent cancer or heart attacks and strokes, the most dangerous complications of artherosclerosis. (Vitamin C also has been touted to prevent the common cold. But many controlled clinical trials have failed to demonstrate that vitamin C supplements produce any differences in the occurrence, severity, or duration of colds.)
Results from a National Institute of Health (NIH) study published in April of this year indicate that 200 mg of vitamin C per day is the optimal intake. In this study, seven healthy young men were kept on a diet with extremely low levels of vitamin C during a four- to six-month period of hospitalization. Their blood and tissue levels of vitamin C were then measured when they took seven different doses of the vitamin, ranging from 30 to 2500 mg daily. The researchers found that the blood concentration of vitamin C reached a plateau at doses of 200 mg a day.
Blood levels did not rise at higher doses because the intestinal absorption of the vitamin decreased while greater and greater amounts of vitamin C were excreted in the urine. The authors of the report suggest that the Recommended Daily Allowance (RDA) of vitamin C be increased from the current level of 60 mg per day, an amount previously selected to prevent the vitamin C-deficiency disease of scurvy, to 200 mg a day to assure maximal blood concentrations and saturation of tissues with vitamin C. This amount of the vitamin can be obtained easily from the diet, without resorting to supplements, by following a diet that regularly contains foods rich in vitamin C, such as citrus fruits, melons, strawberries, dark leafy-green vegetables, sweet potatoes and tomatoes.
Dr. Margolis is professor of medicine and biological chemistry at the Johns Hopkins School of Medicine.
Pub Date: 8/13/96