The best source of vitamin D is the sun. Subcutaneous glands in the skin use sunlight to form pre-vitamin D which is converted to Vitamin D by the liver and kidneys. On a bright summer day, a fair-skinned person needs less than 30 minutes in the sun (without sunscreen) to make the daily requirement of Vitamin D. A dark-skinned person may need two to three hours,. However it’s not that simple because it all depends on where you live. At latitudes above about 40 degrees (like the UK) blood levels of vitamin D decline between October & March not only through paucity of sunlight and covering up to keep warm but because the required ultra violet radiation declines, even in the summer months moisturising creams containing UV protection, sun screens and working indoors often mean we are deficient in this vitamin.

Vitamin D is a vitally important nutrient it protects many tissues in your body against cancer, multiple sclerosis, reduced bone mineral density, impaired cell growth, impaired immune function and chronic inflammation. Vitamin D is required for normal bone growth and a lack of vitamin D can set the stage for osteopenia and osteoporosis. In addition, Vitamin D deficiency has been linked to impaired insulin resistance and an increased risk for type 2 diabetes.

The alternatives to the sun are vitamin D from food, foods that are fortified with vitamin D or the use of supplementation.

The term ‘vitamin D’ refers to not one, but several different forms of the vitamin. Two forms are important in humans: vitamin D2 (ergocalciferol) and vitamin D3 (cholecalciferol). Vitamin D2 is produced by some plant life in response to UV radiation, whereas Vitamin D3 is the form synthesized in your skin in the presence of ultraviolet B rays and is found in foods of animal origin. Both Vitamin D2 and Vitamin D3 are biologically inactive forms of Vitamin D. Before they can become active in your body, they must be converted to active forms in the liver and kidneys.

Research shows that vitamin D3 is superior for the human body, as it is better absorbed and utilized than D2.

If you eat foods of animal origin then oily fish and eggs are a good choice if you eat a plant based diet then mushrooms . Fortified foods generally use vitamin D2 and these products can be rather processed.

Wild Alaskan salmon:

A 4 ounce portion of wild Alaskan salmon will give you just over the recommended daily requirement of vitamin D3

Eggs:

Eggs are another food containing vitamin D3. Choose organic, grass fed chicken eggs, as they contain more vitamin D3 around 12% of the RDA.

Shiitake & maitake:

Both these mushrooms are a good source of vitamin D but mostly D2 Mushrooms react to sunlight in the same way as humans and producing a natural form of vitamin D. It has also been demonstrated that white button mushrooms exposed to ultraviolet B radiation have dramatically increased levels of vitamin D.

Paul Stamets in Mycelium Running writes about the unbelievable effect that sunlight can have on pre-picked mushrooms. In a series of experiments, Stamets discovered that shiitake mushrooms are capable of manufacturing vitamin D even after they have been picked, especially if their gills are exposed to sunlight. Freshly picked shiitake mushrooms contain about 110 IU of vitamin D per 100 grams. Six hours of direct sun exposure can increase vitamin D content in mushrooms by between 100 and 418-fold.

Research has shown that sunlight-exposed mushrooms produce not only D2, but also D4 (with about 60% the biological activity of D3) and small quantities of D3 itself.*

Paul Stamets does not suggest D2 is preferable to D3 but he does point out in “ populations where vitamin D is seriously deficient, sun-exposed dried mushrooms could help address a serious health issue.”

In the UK, the recommended daily amount (RDA) is just 5mcg (200 IU) per day, although up to 25mcg (1000 units) is advised during the winter months, many believe this is too low & therapeutically higher amounts are used. Excess vitamin D is stored in body fat.

Taking a high-quality vitamin D supplement, especially in the winter, is a good idea. Ensure you supplement with natural vitamin D3, vegans and vegetarians should always look to make sure their vitamin D3 supplements are in fact vegan, as many D3 supplements are actually made from animal products – usually sheep wool, vegan alternatives are extracted from lichen.

A good choice is

https://www.wildnutrition.com/products/food-grown-vitamin-d

Research suggests there is an epidemic of Vitamin D deficiency signs include obesity, achy bones, feeling blue, head sweating, and gut trouble. If you think you are deficient in vitamin D it would be wise to have your bloods tested before taking a supplement as too much vitamin D is related to excessive calcium in the blood leading to nausea, vomiting, poor appetite, constipation & kidney stones.

more information here

https://www.vitamindcouncil.org

Resources

Paul Stamets – Mycelium Running – how mushrooms can help save the world

* De Luca HF, Weller M, Blunt JW, Neville PF. Synthesis, biological activity and metabolism of 22,23-3H vitamin D4. Arch Biochem Biophys. [PubMed]