Vitamin D Levels In Mushrooms Increase When Exposed to Sunlight

Vitamin D is essential to maintain strong bones and good health. Although vitamin D can be naturally generated in the body in response to sunlight, many Australians are deficient in vitamin D. Dietary sources of vitamin D become increasingly important during winter, when days are shorter and sunlight less intense.

Like humans, mushrooms also generate vitamin D in response to sunlight. Exposing mushrooms to UV light in particular is known to result in high levels of vitamin D. This trial therefore aimed to determine the time and conditions under which 100 g of fresh mushrooms placed in the sun would produce 10mcg vitamin D. This is enough to meet the daily intake recommended under the Australian Food Standards Code.

Tests were conducted in Sydney during July 2013, using punnets of mushrooms purchased from local supermarkets. Mushrooms were either placed in a single layer on a white plastic plate, left in the punnet but unwrapped, or left in the punnet with wrapping and label in place.

Although the overwrap only blocked around 10% of UV light, the punnet plastic blocked approximately 80% and the label blocked 99%. As a result, only relatively small increases in vitamin D were found in mushrooms left in the punnets.

In contrast, vitamin D increased rapidly in mushrooms placed on a plate in the sun. A 100 g serve of small button mushrooms contained over 10 mcg vitamin D after only an hour. Larger button mushrooms required 2 – 2.5 hours to reach 10 mcg vitamin D. The difference is likely due to their smaller surface area relative to their volume.

Although placing mushrooms in the sun for 1-2 hours resulted in some weight loss, quality was still good with only minor effects on colour, flavor and texture.

Surprisingly, even mushrooms that were not exposed to the sun contained 4-6 mcg vitamin D. This was higher than the levels expected (<1 mcg). Light exposure during packing, transport and display on the retail shelf is likely to have caused this effect. This suggests even mushrooms straight from the supermarket are a significant source of vitamin D.

It was concluded that most people could meet their daily vitamin D needs by;

  • Purchasing 100 g small button mushrooms
  • Placing in a single layer on a white plate
  • Exposing to the sun for 1 hour in the middle of the day
  • Eating the mushrooms

However, researcher warns that not all foods containing vitamin D can provide the amount we need.

“To achieve enough vitamin D you could eat half a kilo of fatty fish such as tuna or salmon, around five tablespoons of margarine or half a litre of vitamin D fortified milk. Mushrooms however, can provide all the vitamin D we need, in just one serve,” concluded Cardwell.

Source: Australian Mushroom Growers