Words on Wellness • Vitamin D
The light is returning and longer days are right around the corner, though the cold keeps us under wraps. Our vitamin D stores, which our skin synthesizes in summer, start to deplete. Vitamin D is an important nutrient that helps regulate calcium and phosphorus levels for bone health. It is also part of a vital immune system, healthy gut and brain health. There are essentially two types: D3 (cholecalciferol) from fish oils, liver, egg yolk, dairy exposed to sun or D3 supplements derived from sheep lanolin, and D2 (ergocalciferol) made from irradiated yeast and added to fortified foods. Only one plant makes Vitamin D2; Mushrooms.
Mushrooms can synthesize D because they contain a “pro-vitamin,” or precursor, called ergosterol that is converted into vitamin D2 when exposed to the sun’s ultraviolet (UV) radiation—similar to how our skin synthesizes D2. All D2 must be activated to D3 in the kidneys for bone building. The best vegan vitamin D is from wild mushrooms—notably chanterelles, maitake, and morels who get natural sun exposure.
Commercially cultivated mushrooms are usually grown in the dark, so they have negligible amounts of vitamin D, however, some commercial growers produce D-enhanced mushrooms by exposing them briefly to UV lamps after harvesting. They are usually labeled “UV-treated” or “high in vitamin D”. D-enhanced mushrooms can contain 400 IU of vitamin D per 3-ounce serving. Just 15 minutes of direct sunlight can produce 200 to 800 IU in 3 ounces of mushrooms (the daily RDA is 600 to 800 IU), regardless of type or season. At least 90 percent of the vitamin is retained after storage and cooking.
A study of the bioavailability of vitamin D2 in mushrooms revealed that ingestion of 2000 IUs of vitamin D2 in mushrooms was as effective in raising and maintaining blood levels of D as ingesting a supplement of 2000 IUs of vitamin D2. Whole button mushrooms synthesize the least D, but sliced buttons are proficient producers if placed with the “gills” facing the sun to increase D production. Shiitake mushrooms do well and have even demonstrated the ability to synthesize D3 in small amounts. Though this D enhancement process may slightly dry and discolor them, you can enhance D2 levels in any mushrooms you buy or pick, by letting them sunbathe in the middle of the day.