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Vitamin C shortage undermines antioxidant defense system.

Imagine eating bran muffins, cereal, and low-fat milk for breakfast; a tuna sandwich and chocolate ice cream for lunch; then chicken teriyaki, rice, rolls, and shortbread cookies for dinner. What's wrong with these meals? Because they don't include any fruits or vegetables, your body would eventually run out of--among other things--vitamin C.

These menus and others like them were specially designed for a 13-week ARS study of the human need for vitamin C. And one of the most important findings, according to ARS research chemist Robert A. Jacob, was that skimping on vitamin C lowers the body's concentration of glutathione. "Glutathione," says Jacob, "is a powerful component of your antioxidant defense system."

Antioxidants defend the body from damaging byproducts of natural internal chemical reactions that go on all the time. Without protective antioxidants, the risk of heart disease, cancer, or inflammatory diseases like arthritis would increase.

Vitamin C is itself a hardworking antioxidant. So are vitamin E, carotenes (compounds your body uses to make vitamin A), the essential mineral selenium, and some enzymes.

This investigation is apparently the first of its kind to link a lowered intake of vitamin C to a decrease in glutathione. "This could happen to anyone who consistently eats less than the 60-milligram Recommended Dietary Allowance of vitamin C," notes Jacob.

Americans most likely to be getting less than the RDA include smokers (cigarette smoke destroys the vitamin) and snackers who prefer foods high in fats and carbohydrates to fruits and vegetables. A small bowl of strawberries, a serving of kale leaves, or a few broccoli florets easily provide the RDA. Other foods especially rich in C include brussels sprouts, green peppers, collards, cauliflower, oranges, lemons, and grapefruit.

A 250-milligram dose of vitamin C--a level also used in the experiment-about equals that furnished in two servings of fruit and three of vegetables, as recommended in the USDA and National Cancer Institute guidelines for healthful eating.

Jacob conducted the study with eight volunteers, men aged 25 to 43, at the ARS Western Human Nutrition Research Center, San Francisco, California. His research colleagues were Susanne M. Henning, Jian Z. Zhang, Ralph W. McKee, and Marian E. Swendseid from the University of California, Los Angeles.

The decline in glutathione showed up within 9 weeks after the volunteers began consuming only 5 to 20 milligrams a day of vitamin C. That's less than one-third the RDA. During this 1ow-C phase of the study, glutathione levels in blood samples fell by 50 percent. "We were surprised to see glutathione change so noticeably in such a short time," Jacob says. Levels doubled when Jacob later boosted volunteers' vitamin C intake to 60 or 250 mg.

The researchers also noted two other signs of oxidative damage. Volunteers' blood levels of NAD and NADP--two macin-derived enzymes--increased when vitamin C levels dropped. "That indicates stress to your antioxidant mechanism," Jacob explains.

Further, quantities of oxidated guanine, another telltale indicator of oxidative damage, about doubled in sperm cells when volunteers went from the study's highest level of vitamin C--250 mg--to the low of 5 to 20 mg. Oxidated guanine levels decreased by 36 percent, however, when Jacob hiked vitamin C intake to 60 or 250 mg a day. Cancer researcher Bruce Ames and colleagues at the University of California, Berkeley, collaborated with Jacob in this work.

"Sperm may be particularly sensitive to oxidation and need vitamin C's protection more than other cells. Perhaps that's why vitamin C levels in semen are about eight times higher than in blood."

To control each volunteer's vitamin C intake throughout the study, only foods that have little if any vitamin C--such as meats, breads, rice, pasta, cookies, cake, and low-fat milk--were served. For part of the time, soft drinks that accompanied each meal were spiked with measured amounts of powdered vitamin C.

Jacob admits that although the meals were tasty, they lacked the attractive colors of fresh produce. Ironically, volunteers had few complaints. "It's sort of a sad commentary," he says, "that no one particularly minded going without fruits or vegetables."---By Marcia Wood, ARS.

Robert A. Jacob and colleagues are with the USDA-ARS Western Human Nutrition Research Center, P.O. Box 29997, Presidio of San Francisco, CA 94129. Phone (415) 556-3531.
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Title Annotation:research by Robert A. Jacob and colleagues
Author:Wood, Marcia
Publication:Agricultural Research
Date:Jun 1, 1992
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