High doses of vitamin C linked to kidney risk

Men who take high doses of vitamin C may face double the risk of kidney stones over men who do not, new research says.

The findings don't directly prove vitamin C is at fault, and the occurrence of kidney stones remains fairly rare, but they raise questions about whether large doses of the vitamin are dangerous.

"Those with a history of kidney stones should consult their doctor before taking high-dose vitamin C supplements," said Agneta Akesson of the Karolinska Institute in Stockholm, Sweden.

Researchers have suspected that large amounts of vitamin C may increase the risk of kidney stones because the body breaks the vitamin down into a substance called oxalate, a component of the stones, Akesson said.

In the study, published online in JAMA Internal Medicine, more than 23,000 Swedish men who were between 45 and 79 in 1997 were tracked. The men, not previously diagnosed with kidney stones, were followed until 2009.

About 900 of them regularly took 1,000-milligram doses of vitamin C, and 31 of them (3 percent) developed kidney stones. Of the rest of the larger group, fewer than 2 percent got kidney stones.

Vitamin C tablets in the 1,000-milligram size are easily found in U.S. drug and health stores. The size provides much more vitamin C than the U.S. government's recommended daily allowance, 75 milligrams to 90 milligrams for most adults.

Akesson said there are no well-documented reasons for anyone to take such high doses of vitamin C. The study doesn't apply to vitamin C from food. -- HealthDay