"How do you know if the mushrooms you buy at the grocery store have been exposed to light? Jennifer Pierce "
Mushrooms do more than top pizza: they’re a valuable source of a vitamin we all need, especially during these short winter days. That’s because the sun is our main source of vitamin D. You will find the vitamin in a few fortified foods, like milk and OJ. And it’s naturally in mushrooms and certain wild-caught fish, such as salmon and mackerel, but there aren’t many D-rich foods. As a result, 80 percent of the U.S. population has seasonal vitamin D deficiency, says Michael Holick, Ph.D., M.D., who heads the Vitamin D, Skin and Bone Research Laboratory at Boston University’s School of Medicine. Healthy D levels keep muscles and bones strong, reduce chronic inflammation and stave off high blood pressure, cardiovascular disease, diabetes, depression and even daytime sleepiness.
Mushrooms—like our skin—make D when exposed to sunlight. That’s why wild mushrooms are high in the vitamin. Commercial mushrooms are typically grown in the dark, but some growers have started exposing them to UV light. (UV-exposed mushrooms have some mention of vitamin D on the label.) You can fortify your own fungi by sunning mushrooms on a windowsill (chop them for maximum surface exposure). One cup (about 3 ounces) of sliced white button mushrooms exposed for an hour between noon and 2 p.m. will end up with approximately 400 IU of vitamin D, according to Holick, who is developing an app to help people make their own D-rich mushrooms (vitdcalculator.com).
Happily, a recent study co-authored by Holick found that eating light-treated mushrooms maintains desirable D levels just as well as supplements or sunshine. That makes these tasty fungi a great—and the only natural and vegan—food source of D.
The daily recommended value for vitamin D is 600 IU/day for most adults, but some experts consider that too low and suggest 1,500 IU/day or more.
The numbers below show the amount of vitamin D contained in 1 cup of chopped raw mushrooms of various varieties.
Morel = 136 IU
Wild Maitake = 786 IU
Portobello = 9 IU, conventional; 384 IU, commercial-light exposed
White Button = 5 IU, conventional; 400 IU, commercial-light exposed
Editor’s Note: If you want to sun mushrooms on a windowsill to increase their vitamin D, the window must be open. Vitamin D cannot be made from sunlight that has passed through glass.
Pictured Recipe: Garlic-Rosemary Mushrooms