Vitamin D has sparked a lot of interest this century, as adequate vitamin D has been linked to a number of benefits beyond healthy bones and the prevention of rickets and osteoporosis, such as a decreased risk of heart disease, type 2 diabetes, hypertension and colorectal cancer (Lee 2008; Wang 2008; Dobnig 2008; Holick 2010). In November 2010 the Institute of Medicine in the US raised the daily requirement levels for vitamin D. The recommended levels are expected to rise in Australia too when the RDIs are next reviewed.
The adult Recommended Dietary Intake for vitamin D ranges from 5-15 mcg, with more being needed by older people. Compare that to the typical vitamin D dietary intake of 2-3 mcg daily by adults (Nowson 2002). The common dietary form of vitamin D in Australia is cholecalciferol (vitamin D3) available from table margarine, canned fish and eggs (Shrapnel 2006). Both vitamin D2 and D3 are offered as supplemental vitamin D in Australia.
Mushrooms too, are a source of vitamin D. It is quite natural for ergocalciferol (vitamin D2) to be found in mushrooms. Wild mushrooms, through the action of sunlight, convert their abundant ergosterol to ergocalciferol. Wild mushrooms in Europe commonly have 2-40 mcg vitamin D/100g (Mattila 1994; Mattila 2002; Teichmann 2007). Even store-bought mushrooms are able to generate over 20 mcg per serve after being placed in sunlight for a couple of hours in the midday sun (Simon 2011). Once consumed, the vitamin D2 is converted to 1, 25 (OH) ergocalciferol. Both vitamin D2 and D3 act in the same way in the body.
There is a small amount of vitamin D in cultivated mushrooms as they don’t need light to grow. Farmers generally don’t subject their mushrooms to light other than during growing operations and harvesting. However, if these mushrooms are exposed to a short burst of ultraviolet light they generate in excess of the daily recommended intake for vitamin D.
Vitamin D-enhanced mushrooms are now available in supermarkets in Australia, the US and Canada, providing at least the daily allowance of vitamin D in a single serve. Farmers mimic nature by passing the mushrooms under a UV light. Only 2-3 seconds is all it takes for the D2 conversion process to be activated.
Following research at the University of Western Sydney showing that UV light boosts the vitamin D levels in mushrooms, the Australian mushroom industry refined the US technique to their growing system so consumers in Australia have had D-enhanced mushrooms in selected stores since September 2011 (Koyyalamudi 2009; Koyyalamudi 2011).
The vitamin D in mushrooms is easy to absorb (Outila 1999; Jasinghe 2005; Koyyalamudi 2009) and support bone growth (Calvo 2012). There is at least a 85% retention of vitamin D in wild mushrooms after frying for five minutes (Mattila 1999). Furthermore, there is very little loss of vitamin D2 when the mushrooms are refrigerated for eight days (Koyyalamudi 2009) or even three months (Mattila 1999). This means that mushrooms can be a very useful source of vitamin D to the consumer, whether eaten raw or cooked.
Vitamin D mushrooms will become a simple and delicious way for Australians to get 100% of their daily vitamin D needs, especially if they are unable to get adequate sun exposure during the day.