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Place Mushrooms in Sunlight to Get Your Vitamin D: Part Two

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How much vitamin D can 100 grams of fresh mushrooms make from sunlight? A lot, but a lot more when mushrooms are dried, pulverized, and then exposed to UVB light lamps. Caution: Using UVB light lamps can cause damage to your eyes and skin. Do not attempt this without taking necessary precautions.

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Robert Beelman at Penn State University was one of the pioneers who learned that pulsing high intensity beams of UV could generate vitamin D (and also -- bonus -- surface-sterilize the mushrooms). Thanks in large part to his work, UV-exposed mushrooms -- primarily the fresh button variety -- are increasingly available in grocery stores. When we ranked the vitamin D concentrations of shiitake exposed to no light, exposed to sunlight with gills up, and exposed to continuous UVB light after slicing, the results were impressive: more than a six-fold increase under UVB light compared with sunlight.

These results make sense. When mushrooms were sliced, more ergosterol-rich surface area was exposed. The indoor UV light was more intense than sunlight. The combination of these resulted in more vitamin D being produced. Although up to 12 hours of sun exposure to upside-down (gills up) shiitakes created 46,000 IU of vitamin D, I am sure sliced ones would give you more, as the surface area would increase. However, the sun is a convenient source of UVB, whereas setting up a UVB light chamber is not.

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Here is how to do it:

1. Obtain fresh organic shiitake, maitake, button, oyster, shimeji or other mushrooms.

2. On a sunny day in June, July or August, slice the fresh mushrooms. Place them evenly on a tray exposed directly to the sun from 10 a.m. to 4 p.m.

3. Before nightfall, cover the mushrooms with a layer of cardboard to block moisture from dewfall.

4. The next clear day repeat exposure to the sun from 10 a.m. to 4 p.m.

5. Remove the mushrooms and finish drying (if necessary in a food dehydrator until they are crispy).

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6. When thoroughly dry, store in a glass jar or sealed container. Adding a tablespoon of uncooked rice as a moisture absorber will help keep the mushrooms dry. The mushrooms should be good for a year or more, depending upon conditions.

7. Take 10 grams daily per person, about a small handful. Rehydrate in water for one hour. The mushrooms will swell. Then cook as desired.

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A natural question to ask is how much of the vitamin D from consuming mushrooms makes it into the bloodstream. Comparing 26 people who took a vitamin D2 supplement to 26 others ingesting vitamin D-enriched mushrooms four times per week for five weeks, researchers at the University Medical Center in Frieburg, Germany found that the serum levels of vitamin D were similar. They used button mushrooms exposed to UV light that resulted in 20,000 IU/100 grams fresh weight. Subjects ingested 120 grams fresh (≈24,000 IU) of vitamin D-enriched mushrooms, which is about a quarter of a pound, roughly a handful. The results showed similar levels of vitamin D were absorbed in the blood in both groups: Those who ingested a supplement in pill form and those who put freshly-cooked mushrooms in soup. At the end of the study, both groups' serum vitamin D levels increased to ~50 nmol/L, which is considered to be a healthy baseline level. A general consensus amongst many health care practitioners is that you need to replenish your vitamin D so blood serum levels are between 50 and 125 nmol/L of 25-hydroxyvitamin D. Care should be taken to avoid over-supplementation, as serum levels over 125 nmol/L can be hazardous (see chart).

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Mushrooms are not only wonderful sources of vitamin D, but they offer us many opportunities for maintaining and improving health. Whether you expose cultivated mushrooms or wildly-harvested edibles, both become jam-packed with vitamin D after light exposure. Mushrooms are truly super foods!

Recommended website:
NIH Office of Dietary Supplements Fact Sheet on Vitamin D

References Used for This Blog:

  • Beelman, R. & M. Kalaras. "Post-harvest Vitamin D Enrichment of Fresh Mushrooms." HAL Project# MU07018 (April 30, 2009), Penn State University.
  • U.S. Mushroom Council & Australian Mushroom Growers Association.
  • Holick, M.F. "Vitamin D Deficiency." New England Journal of Medicine, 2007; 357(3):266-81.
  • Institute of Medicine. "Dietary Reference Intakes for Calcium and Vitamin D." 2010. Washington, DC.
  • Lappe J.M., Travers-Gustafson D., Davies K.M., Recker R.R., Heaney R.P. "Vitamin D and calcium supplementation reduces cancer risk: results of a randomized trial." American Journal of Clinical Nutrition. 2007; 85(6):1586-1591.
  • Rejnmark, L. "Vitamin D with Calcium Reduces Mortality: Patient Level Pooled Analysis of 70,528 Patients from Eight Major Vitamin D Trials." Journal of Clinical Endocrinology and Metabolism. Published online May 17, 2012, doi: 10.1210/jc.2011-3328.
  • Stamets, P. & G. Plotnikoff. "Anticancer Medicinal Mushrooms Can Provide Significant Vitamin D 2 (Ergocalciferol)." International Journal of Medicinal Mushrooms. 2005; 7(3):471-472.
  • Stamets, P. "Notes on Nutritional Properties of Culinary-Medicinal Mushrooms" International Journal of Medicinal Mushrooms. 2005; 7(1&2):103-110.
  • Stamets, P. Mycelium Running: How Mushrooms Can Help Save the World. 2005. Ten Speed Press, Berkeley.
  • Urbain, P., et al. "Bioavailability of vitamin D2 from UV-B-irradiated button mushrooms in healthy adults deficient in serum 25-hydroxyvitamin D: a randomized controlled trial." European Journal of Clinical Nutrition. 2011; 65:965-971.

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