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Researchers found that a single serving of white button mushrooms will contain 869 percent the daily value of vitamin D once exposed to just five minutes of UV light after being harvested.
updated 4/18/2006 11:10:50 AM ET 2006-04-18T15:10:50

Mushrooms may soon emerge from the dark as an unlikely but significant source of vitamin D, the sunshine vitamin that helps keep bones strong and fights disease.

New research, while preliminary, suggests that brief exposure to ultraviolet light can zap even the blandest and whitest farmed mushrooms with a giant serving of the vitamin. The Food and Drug Administration proposed the study, which is being funded by industry.

Exposing growing or just-picked mushrooms to UV light would be cheap and easy to do if it could mean turning the agricultural product into a unique plant source of vitamin D, scientists and growers said. That would be a boon especially for people who don't eat fish or milk, which is today the major fortified source of the important vitamin.

One grower predicted the pilot project, if supported by further research, could give consumers a radically different reason to buy mushrooms, now sought out for being low in fat and calories.

"They eat them for what they don't have, versus what they do have," said Joe Caldwell, vice president of Monterey Mushrooms. The Watsonville, Calif. company is the nation's largest producer of fresh mushrooms.

The ongoing work so far has found that a single serving of white button mushrooms — the most commonly sold mushroom — will contain 869 percent the daily value of vitamin D once exposed to just five minutes of UV light after being harvested. If confirmed, that would be more than what's in two tablespoons of cod liver oil, one of the richest — and most detested — natural sources of the vitamin, according to the National Institutes of Health.

Details were being presented this week at the FDA's annual science forum. The FDA proposed the research, which was funded by the Mushroom Council, as the agency looks for ways to increase the amounts of vitamin D consumed by Americans.

"This could be it," said Robert Beelman, a Penn State food scientist who's spent more than a decade working to give mushrooms their own "nutritional identity."

Sunshine is a significant source of vitamin D, since natural UV rays trigger vitamin D synthesis in the skin. Mushrooms also synthesize vitamin D, albeit in a different form, through UV exposure. Growers typically raise the mushrooms indoors in the dark, switching on fluorescent lights only at harvest time. That means they now contain negligible amounts of vitamin D.

Research, including new findings also being presented at the conference, consistently has shown that many adult Americans do not spend enough time outside to receive enough UV exposure needed to produce ample vitamin D. The problem is especially acute in winter.

That worries health officials and not only because of rickets, the soft-bone disease linked to vitamin D deficiency that was a scourge in decades past. Vitamin D is increasingly thought to play a role in reducing the risk of osteoporosis, cardiovascular disease and tooth loss, as well as in reducing mortality associated with colon, breast, prostate and other cancers.

Beelman said his research has shown that exposing growing mushrooms to three hours of artificial UV light increases their vitamin D content significantly. That could be easier than exposing fresh-picked mushrooms to light, Beelman said. The only drawback is that the white button mushrooms — like people — tend to darken with increased UV exposure, he added.

Copyright 2006 The Associated Press. All rights reserved. This material may not be published, broadcast, rewritten or redistributed.

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