Women Should Up Vitamin C Intake

MONDAY, Aug. 13, 2001 (HealthDayNews) -- Ladies, it's time to load up on the fruits and veggies.

New research from the National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK) provides evidence that the current recommendation -- that women consume 75 milligrams of vitamin C every day -- is not sufficient. Women should take equal doses to men, it finds.

The study, which appears in the Aug. 14 issue of the Proceedings of the National Academy of Sciences, is the first to focus on how much vitamin C women need. The existing recommendations for women are based on research data for men.

The Food and Nutrition Board of the National Academy of Sciences, which makes recommendations for both the United States and Canada, raised men's recommended daily allowance (RDA) of vitamin C from 60 milligrams to 90 mg in April 2000, based on data suggesting that the additional milligrams would achieve maximum tissue saturation.

But because the data came from testing done on men, the board had to extrapolate from that, using body weight, to set the new RDA for women at 75 mg daily.

Dr. Mark Levine, the chief of the NIDDK's Molecular and Clinical Nutrition Section in Bethesda, Md., led the latest study. He has spent several years working on the RDA of various vitamins. "As a physician-scientist, I see nutrition as a way to prevent illness," he says.

The earlier recommendations on vitamin C were based on the principle of preventing a deficiency and providing a small extra amount of the vitamin, Levine adds.

"We think a better way is [to] base vitamin C recommendations on what the vitamin does," he says.

To do that, says Levine, the researchers need to find out which dose results in which concentrations in the body and what those concentrations do in the body.

Levine studied vitamin C intake in men in 1996, providing data that the Food and Nutrition used to devise the current RDAs.

This time, he studied vitamin C intake in women. Fifteen healthy women between the ages of 19 and 27 volunteered for the study, which demanded that they remain in the hospital for approximately six months so researchers could control their dietary intake.

While in the hospital, the women consumed a special diet that included virtually no vitamin C. The researchers then tested the effects of daily vitamin C doses ranging between 30 mg and 2,500 mg.

Levine and his colleagues gathered data to plug into the Food and Nutrition Board's formula for vitamin C intake. For each dose, they determined how much vitamin C can be found in certain immune cells, and how much vitamin C was excreted in urine samples.

Based on finding how the different vitamin C doses were metabolized, and applying the formula that the Food and Nutrition Board uses to calculate the ideal daily dose, Levine and his colleagues suggest that the current RDA of 75 mg for women should be increased to 90 mg.

But the researchers still don't have data about how different doses of vitamin C affect various clinical outcomes. Indirect measures do exist, such as the fact that vitamin C is found in fruits and vegetables, and that a diet rich in fruits and vegetables has health benefits.

"People should eat five servings of fresh fruits and vegetables a day or more," says Levine. He adds that it's not clear whether people are more likely to absorb the vitamin through their diet or from a supplement.

But he says, "We don't recommend that people take vitamin C as a supplement, unless there's some reason they can't or won't eat fruits and vegetables."

Dr. Ishwaral Jialal, chairman of the vitamin C subcommittee of the Food and Nutrition Board's Panel on Antioxidants and Related Nutrients, praises the study.

"It's the first study to show in young, healthy women that they need 90 mg of vitamin C," he says.

But he cautions that one single study is unlikely to convince the Food and Nutrition Board to change the current RDA, and he also points out that the new study didn't include older women.

However, if future studies provide evidence that supports Levine's findings, Jialal says that the committee may meet to consider changing the RDA for women.

Levine hopes to follow up his study with research on the health outcome of various vitamin C doses, and the most effective RDA of vitamin C in other populations, including children and the elderly.

What To Do

The Food and Nutrition Board set the adult upper-intake level of vitamin C at 2,000 mg per day. Higher levels could cause side effects, including diarrhea.

A recent Department of Agriculture nutrition survey estimated that 39 percent of men and 43 percent of women don't get enough daily vitamin C. The best way to increase your intake of vitamin C is to eat a diet rich in fresh fruits and vegetables.

For information on the current RDAs, visit this Web page from the Medical College of Wisconsin.

The American Dietetic Association can provide some information about whether you need a multivitamin or mineral supplement, or you can check out this Food and Drug Administration guide to dietary supplements.