Maybe you've heard about a fairly recent food-industry practice where mushrooms are exposed to ultraviolet light to enhance their vitamin D content--your first reaction might have been, "What on earth?!"
Mushrooms and vitamin D
Why mushrooms? It turns out that the cell membranes of these tasty fungi contain a natural substance called ergosterol that is sort of like our cholesterol. And researchers have found that when mushrooms are exposed to ultraviolet (UV) light, their ergosterol is converted into vitamin D2, much like when the 7-dhydrocholesterol in our skin is transformed into vitamin D3 when we're out in the sun. Some sources suggest that UV-treated mushrooms may contain as much as 3,500 international units (IUs) of vitamin D per serving when exposed to UV light for long periods.
Now, in controlled experiments, researchers are seeing whether mushrooms enhanced in this way can help increase vitamin-D levels in the people who eat them.
The power of vitamin D
What's all the fuss about vitamin D? Well, vitamin D has been found to play a part in over 2,000 reactions within our body. Studies also suggest that, besides its well-known ability to help in treating bone diseases, vitamin D can also assist in preventin:
type 2 diabetes
high blood pressure
Higher overall death rates have been associated with vitamin-D deficiency as well, and some evidence suggests that the signs and symptoms of fibromyalgia might be due in part to a vitamin-D deficiency--or, that the severity of this disorder can be vastly lessened if a vitamin-D deficiency is found and treated.
Get yours tested
The proper lab procedure for testing vitamin D levels is a blood test called 25-OH vitamin D. It's worth noting that, whereas some labs may call levels of around 32 nanograms per milliliter (ng/mL) as normal, experts like Michael Hollick, MD, PhD, at Boston University, recommend aiming for a level of 50 ng/mL to 80 ng/mL. Some researchers even recommend allowing levels to approach 100 ng/mL. (A blood level consistently above 200 ng/mL however, is considered potentially toxic.)
Foods rich in vitamin D
According to the NIH, the following are worth consuming for their vitamin D content:
Cod liver oil, 1 tablespoon (1,360 IUs of vitamin D)
Salmon (sockeye), cooked, 3 ounces (794 IUs)*
Mushrooms that have been exposed to ultraviolet light to increase vitamin D, 3 ounces (400 IUs) (not yet commonly available)
Mackerel, cooked, 3 ounces (388 IUs)
Tuna, canned in water, drained, 3 ounces (154 IUs)
Vitamin D-fortified milk (nonfat, reduced fat, or whole), 1 cup (115-124 IUs)
Vitamin D-fortified orange juice, 1 cup (amount of added vitamin D varies) (100 IUs)
(*Note: Research has suggested that farm-raised salmon might contain only 25 percent of the vitamin D that's found in wild Alaskan salmon.)
UV-treated mushrooms might have an important role in helping to decrease the prevalence of vitamin D deficiency. But, in any case, please get your levels of 25-OH vitamin D checked regularly.