High-dose vitamin C linked to kidney stones in men

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File this under “if a little bit is good, a lot isn’t necessarily better:” taking high-dose vitamin C appears to double a man’s risk of developing painful kidney stones.

In an article published yesterday in JAMA Internal Medicine, Swedish researchers detail a connection between kidney stone formation and use of vitamin C supplements among more than 23,000 Swedish men. Over an 11-year period, about 2% of the men developed kidney stones. Those who reported taking vitamin C supplements were twice as likely to have experienced the misery of kidney stones. Use of a standard multivitamin didn’t seem to boost the risk.

The average man needs 90 milligrams (mg) of vitamin C a day; the average woman 75 mg. The vitamin is important for making and repairing connective tissue, skin, and bones. It also helps the body absorb iron. Good food sources include red peppers, papaya, and citrus fruits. Vitamin C supplements can deliver 10 times or more of the daily requirement.

In part because of the tireless but misguided efforts of Nobel laureate Linus Pauling and others, many people believe that extra vitamin C can prevent colds, supercharge the immune system, detoxify the body, protect the heart, fight cancer, and more. To date, though, the evidence doesn’t support claims that extra vitamin C is helpful. Despite that, vitamin C represents the biggest single category of vitamin and mineral sales; Americans bought more than $200 million worth of it last year.

Risk is real, benefits aren’t

The Swedish study isn’t the first to link vitamin C with kidney stones. A similar connection was observed in men by Dr. Gary C. Curhan and colleagues at the Harvard School of Public Health. Curiously, in an almost identical study in women, Curhan’s team didn’t find any association between vitamin C intake and kidney stones.

Kidney stones form for a variety of reasons. Genes matter, as do gender (men get them more than women), weight (obesity boosts the risk), and diet (eating a lot of animal protein, not drinking enough fluids). The most common type of stone is a mixture of calcium and oxalate, a substance found in many foods. Some people break down vitamin C into oxalate, which may explain the connection with kidney stone formation.

Is there enough evidence to warn men, at least, from taking vitamin C supplements? Yes, says Dr. Curhan. “High dose vitamin C supplements should be avoided, particularly if an individual has a history of calcium oxalate stones.”

In a commentary accompanying the vitamin C article, Dr. Robert H. Fletcher, emeritus professor of ambulatory care and prevention at Harvard Medical School, made the point a different way. If there’s truly a cause-effect relationship, then one of every 680 people who take high-dose vitamin C (also known as ascorbic acid) would develop kidney stones. “This is not an insignificant risk,” Fletcher writes. “But more to the point, is any additional risk worthwhile if high-dose ascorbic acid is not effective?”