Vitamin D - the sunshine vitamin
- daphne3144
- Jun 5
- 3 min read
by Daphne Lambert
Production of Vitamin D, an essential nutrient, is stimulated when our skin is directly exposed to sunlight, or more specifically, UVB rays. Vitamin D is known to protect your body against cancer, multiple sclerosis, reduced bone mineral density, impaired cell growth, weakened immune function and chronic inflammation. Vitamin D deficiency has been linked to insulin resistance and an increased risk of type 2 diabetes and potentially increased risk of death from all causes.①
The term ‘vitamin D’ refers to not one, but several different forms of the vitamin. Two important forms for humans are vitamin D2 (ergocalciferol) and vitamin D3 (cholecalciferol). Vitamin D3 is the form synthesised in your skin when exposed to the sun. Research shows that vitamin D3 is is better absorbed and utilised by the human body than vitamin D2.② Both vitamin D2 and vitamin D3 are converted by the liver to a third form of vitamin D, known as 25-hydroxyvitamin D this is then converted in the kidneys to its active form calcitriol (1,25 hydroxy vitamin D.) The active form of vitamin D binds with the receptor on the genes to switch on different activities within the body. Vitamin D has been found to influence over 200 genes.③
On a bright summer day, a fair-skinned person, not wearing sunscreen, will make adequate vitamin D if legs and arms are exposed to the sun, for 15-20 minutes. A dark-skinned person may need two to three hours. Sunscreen will block vitamin D production but not entirely. It is, of course, important not to to get sun burnt. Adequate sunshine for vitamin D production all depends on where you live.
At latitudes above about 42 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.
Vitamin D3 is found in foods of animal origin. People who choose not to eat these foods need to make sure they have a reliable source of this vitamin. Irrespective of diet research shows that there is a worldwide deficiency of vitamin D which has reached epidemic proportions.④
The only reliable vitamin D food source for those who choose not to eat anything of animal origin are mushrooms.
Research has shown that sunlight-exposed mushrooms produce not only D2, but also D4 (with about 60% the biological activity of D3).⑤ Shiitake mushrooms, if the gills are exposed to the sun, can make D2, D3, and D4. All commonly consumed mushrooms seem to have provitamin D4 (the substance that can convert into D4) and the ability to convert it given the right UV conditions.⑥
For many people who choose a plant based diet the best option, especially in the winter, is to take a high-quality vitamin D3 supplement. Many D3 supplements are actually made from animal products, usually sheep wool, vegan alternatives are extracted from lichen.
References:
1. Ben Schöttker et al., published in the BMJ, 17 June 2014 https://www.bmj.com/content/348/bmj.
2. Vitamin D3 Is More Potent Than Vitamin D2 in HumansRobert P. Heaney. https://academic.oup.com/jcem/article-abstract
4. Dr Zahid Naeem - Vitamin D Deficiency- An Ignored Epidemichttps://pmc.ncbi.nlm.nih.gov/articles/PMC3068797/
5. De Luca HF, Synthesis, biological activity and metabolism of 22,23-3H vitamin D4. https://pubmed.ncbi.nlm.nih.gov/4298487/
6. Phillips, Katherine M. Vitamin D4 in mushrooms.
