Mushrooms are the only food in the produce aisle that naturally contains vitamin D, the sunshine vitamin thats essential for bone health and associated with a wide range of other possible health benefits. Levels of vitamin D in most mushrooms are too low, however, to make a significant contribution toward your daily recommended 600 IU (800 over age 70). But new research shows that mushrooms briefly exposed to ultraviolet light in processing can produce more vitamin D than found in a glass of fortified milk.
Its not easy to get 600 to 800 IU of vitamin D daily from food sources, says Bess Dawson-Hughes, MD, director of Tufts HNRCA Bone Metabolism Laboratory. Its important, because in addition to bone health we see that D affects muscle strength and the risk of falling. Low levels of vitamin D have been associated with a range of chronic diseases, such as diabetes, hypertension, heart disease, some cancers, infections and autoimmune problems.
ADD UV TO GET D2: Mushrooms, as well as other fungi, seaweed and yeast, contain a precursor to vitamin D called ergosterol, which exposure to ultraviolet light converts to vitamin D2 (ergocalciferol)- much as the human skin uses sunlight to synthesize vitamin D3. Although recent research has suggested that D3 is a more potent form, D2 can still raise blood levels of the circulating form of the vitamin that the body uses. Testing by the USDAs Beltsville (MD) Human Nutrition Research Center found that a few types of ordinary mushrooms- notably morel and chanterelle-contain about 200 IU of vitamin D2 in 100 grams (a little over three ounces). Amounts varied widely by producer and geography, however, and most common white button and portabella mushrooms had less than 10 IU. Portabella mushrooms exposed to ultraviolet light for 15-20 seconds, on the other hand, all contained significant quantities of vitamin D2-from 124 to 1,022 IU per 100 grams.
At the recent Experimental Biology meeting in Boston, Michael Holick, MD, PhD, of Boston University, and colleagues presented findings from a small clinical trial showing that the D2 in mushrooms can boost blood levels of the vitamin as much as supplements. They compared capsules of powdered white button mushrooms, exposed to ultraviolet light, with D2 and D3 supplements.