The Lowdown on Vitamin D
The Canadian Cancer Society recommends that light-skin people should obtain 1000 IU (International Units) per day during fall and winter, and dark-skin people should obtain 1000 IU year-round.
Health Canada recommends the following for Vitamin D Consumption:
The Daily Recommended Intake for Vitamin D
Since 1920, it has been known that the main role of Vitamin D is to work with Calcium and Phosphorus to make strong bones. Recent findings suggest that Vitamin D also helps to:
- prevent bone fractures
- reduce the risk of diabetes in young people
- protect against heart disease
- reduce the risk of multiple sclerosis
- improve lung function
Mushrooms Have Vitamin D
Mushrooms are the only vegetable that contains Vitamin D, naturally. All other natural food sources of Vitamin D are of animal, poultry or seafood origin. Also, some foods, such as milk, orange juice and cereals may be fortified with Vitamin D, up to 100 IU.
Cultivated mushrooms contain a plant sterol called ergosterol, which is the precursor of Vitamin D². In fresh mushrooms, ergosterol is stimulated to convert to Vitamin D² by ultraviolet light, either from sunlight or artificial lights.
The vitamin D levels of common varieties of mushrooms are listed below for a standard 100 g serving. 200 IU recommended for adults up to the age of 50.
Adding Vitamin D to Fresh Mushrooms
It has been demonstrated in recent studies that the level of Vitamin D² in White/Brown mushrooms can be increased significantly (up to 100% of the Daily Value), by exposure to ultraviolet light for a few minutes, either pre-harvest or post-harvest. When this technology is perfected, Super-D mushrooms may be available, to the public, as a vegetable source of Vitamin D.
How the World is Working to Add More Vitamin D to Mushrooms
In order to incorporate a UV treatment system into a commercial mushroom farm, some technical questions must be answered. For example:
- Where is the best location for UV-treatment, in the growing rooms (pre-harvest) or in the packing room (post-harvest)?
- What is the best source of UV light, distance from the mushrooms and duration of exposure?
- What is the shelf life of treated mushrooms?
- Do white mushrooms discolour? How much?
- If so, are brown mushrooms the preferred variety?
- Does the level of Vitamin D decrease with time?
In Canada, Mushrooms Canada is sponsored research at the Guelph Food Technology Centre (GFTC) to determine the appropriate UVB light dosage to achieve 100% RDA levels (400 IU) in fresh, white and brown mushrooms. The study includes shelf-life, discolouration and microbiology of the treated products.
- Commercialization of Vitamin D Enhanced Mushrooms by UV light Treatment. Mushrooms Canada and the Guelph Food Technology Centre.
The Australian Mushroom Growers Association (AMGA) has researched the intermittent UV-light exposure in a growing room, pre-harvest. Vitamin D² will be measured in the mushrooms, 4 and 8 days post-harvest. The objective was to license a Vitamin D² process for mushroom growers.
- Critical Issues for Intending Producers of Vitamin D Mushrooms. Warmish Scientific.
In the USA, The Mushroom Council and the Agricultural Research Service of the USDA are studied the time and dosage of UVB light treatment up to 4 days post-harvest and Vitamin D² degradation during storage.
- Vitamin D2 formation from post-harvest UV-B treatment of mushrooms (Agaricus bisporus) and retention during storage. J Agr Food Chem 2008;25:4541-4.