Most of us living in northern climes suffer from vitamin D deficiency, particularly in the sun starved winter months. Vitamin D is essential for the immune system, strong healthy bones, teeth and the absorption of calcium. More recently it has also been found to help to boost immunity to COVID19. According to a recent Oireachtas Health Committee’s report, “low levels of vitamin D have been linked to worse health outcomes in relation to Covid-19, and this is why the issue needs to be addressed urgently”.

Previous US Health studies have found that, “Mushrooms exposed to the sun can provide as much vitamin D as a health supplement”. In one study, 30 adults were given a daily capsule for 12 weeks containing either 2,000 units of vitamin D, or sun-exposed mushroom powder with high-levels of the nutrient. At the end of the trial, there was no significant difference in the participants’ vitamin D levels. The study lead author Dr Michael Holick went on to say that “These results provide evidence that ingesting mushrooms which have been exposed to ultraviolet light and contain vitamin D2, are a good source of vitamin D that can improve the vitamin D status of healthy adults. Furthermore we found ingesting mushrooms containing vitamin D2 was as effective in raising and maintaining a healthy adult’s vitamin D status as ingesting a supplement that contained either vitamin D2 or vitamin D3”. These findings were presented at the American Society for Biochemistry and Microbiology meeting in Boston and also published in the journal of Dermato-Endocrinology. Dr Holick also stated that mushrooms continue to produce the nutrient even after they are harvested as long as they are placed in direct sunlight.

Another study at Penn State University found that by exposing a single serving of mushrooms to direct sunlight for an hour or two anytime between 10AM and 3PM will boost the vitamin D levels to provide 824% of the recommended daily value for an adult. Interestingly that figure was just for white button mushrooms, oyster and shiitake mushrooms achieved even higher multiples.

For those of us who consume wild mushrooms it is likely that the sunshine boost is already present assuming they that they have grown in natural light conditions. Furthermore it seems that there is no significant decrease in the vitamin D levels caused by drying and/or cooking mushrooms.