☀️Calciferol ("Vitamin" D)

Calcitriol is a hormone that your body naturally produces from sunlight. Dietitians recommend eating foods with calciferol ("vitamins" D2/D3) to ensure safe and adequate production of calcitriol, but it is also possible to produce enough calcitriol from sunlight exposure alone.

Sources

Raw - Mushrooms can contain "vitamins" D2, D3, and D4 if exposed to UVB rays (such as sunlight) - Nutritional yeast (which is fungal) can contain ergocalciferol (D2) - Lichen (which is an alga) contains cholecalciferol (D3) Fortified According to the Academy of Nutrition and Dietetics, "fortified foods and drinks provide most of the vitamin D in our diets". Ergocalciferol is fortified in plant-based foods including: - breakfast cereals - orange juice - plant-based milks (e.g. soy milk) - tofu Supplements Cholecalciferol from lichen can be used to produce vegan cholecalciferol supplements. (There are currently non-vegan cholecalciferol supplements made by exploiting sheep for their wool, so lichen gives us a great alternative.) Cholecalciferol is better than ergocalciferol for supplementing since it's more effectively absorbed by our bodies. Ergocalciferol is also available as a vegan supplement. It is commonly produced by exposing yeast to UVB rays.

Recommendations

Dietitians generally recommend getting calciferol in your diet to ensure adequate and safe production of the essential hormone calcitriol. You don't need both ergocalciferol (D2) and cholecalciferol (D3) - you just need one. In practice, this means incorporating mushrooms, nutritional yeast, and/or foods fortified with vegan calciferol (such as soy milk) into your diet where possible. You can also supplement. "Vitamin D status depends on sunlight exposure and intake of vitamin D-fortified foods or supplements. [...] Dietary and supplemental sources of vitamin D are commonly required to meet the needs of this nutrient. [...] If sun exposure and intake of fortified foods are insufficient to meet needs, vitamin D supplements are recommended, especially for the older adults [...] some experts recommend daily intakes of vitamin D of 1,000 to 2,000 IU, or even more." https://www.jandonline.org/article/S2212-2672(16)31192-3/pdf

Hormone or Vitamin? Dietary Importance

Vitamins are essential nutrients which we must get through our diets. Because our bodies can manufacture calcitriol via exposure to sunlight, it is not a vitamin. It is more accurately called a hormone. However, dietary sources of calciferol can become essential for the production of calcitriol where there is inadequate UVB exposure. This is particularly relevant to those living away from the equator where the angle of the earth to the sun results in more UVB rays scattering in the atmosphere before reaching us. (Also of note, particularly to people working office jobs, you cannot get UVB exposure through most glass because the material is opaque to those wavelengths.) Other concerns - such as avoiding sunburn, skin aging, and skin cancer - can make dietary sources even more important.

In 2018 it was found that of people hospitalized in the US (mostly non-vegans), 40% were deficient in "vitamin D". It was also found that over 90% of people ingest less than the average requirement. This further drives home the importance of getting calciferol via one's diet, whether by raw food sources, fortified foods, or supplements. "From a population of 4962 participants, age ≥20 years, who were hospitalized between 2011 and 2012 [...] analyzed from a group of approximately 5000 individuals through the administration of standardized interviews and physical examinations that include laboratory tests utilizing blood and urine specimens [...] Of the 4962 participants interviewed in this study by NHANES 2011-2012, 1981 (39.92%) were vitamin D deficient (serum levels less than 50 nmol/L), a proportion that has remained consistent since 2005-2006, when NHANES found 40% of the population to be vitamin D deficient" https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6075634/ "2013–2016 NHANES data showed that 92% of men, more than 97% of women, and 94% of people aged 1 year and older [in the US] ingested less than the EAR [Estimated Average Requirement] of 10 mcg (400 IU) of vitamin D from food and beverages" https://ods.od.nih.gov/factsheets/VitaminD-HealthProfessional/#h2 https://www.healthline.com/health/vegan-vitamin-d https://www.healthline.com/nutrition/vitamin-d-foods-for-vegetarians https://www.health.harvard.edu/newsletter_article/vitamin-d2-or-d3 https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6213178/ https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3411670 https://www.vegansociety.com/resources/nutrition-and-health/nutrients/vitamin-d https://www.ars.usda.gov/ARSUserFiles/80400530/pdf/usual/Usual_Intake_gender_WWEIA_2013_2016.pdf

Chemistry

Bodily Synthesis When our skin is exposed to ultraviolet B rays (such as sunlight), it can manufacture cholecalciferol and ultimately (through our liver and kidneys) calcitriol. Dietary Intake The body can metabolize forms of "vitamin D" into the hormonally active form of calcitriol. The most well-studied forms (and forms with the best evidence of benefit) of "vitamin D" are ergocalciferol (D2) and cholecalciferol (D3). Cholecalciferol is better than ergocalciferol since it's the more effectively absorbed by our bodies. There are other forms of "vitamin D" that we can metabolize: "vitamins" D4 and D5 are present in some plant-based foods, such as certain mushrooms that have been exposed to UVB. There is not enough research into these forms of "vitamin D", but from what we know so far it seems that calciferol (D2/D3) is the best way to ensure production of calcitriol.

Vocabulary

The term "vitamin D" is highly ambiguous and misleading. (Is it a vitamin or a hormone since our body can produce it outside of our diet anyway? Are we talking about the hormone our body needs or one of the prohormone compounds our body can use to help produce more? Which prohormone compound are we even taking about since there are multiple?) Therefore this article introduces several terms some people may be unfamiliar with in the hopes of being more precise. "Vitamin D": Can refer to the hormone calcitriol (which is not a vitamin), or (as frustratingly ambiguous as this is) to any of the prohormone compounds ("vitamins") D1, D2, D3, D4, and/or D5. Calcitriol: A hormone necessary for maintaining the human body. Calcitriol is the biologically active form of "vitamin D" that the body produces from prohormone compounds. Calciferol: Refers to ergocalciferol (D2) and/or cholecalciferol (D3). When talking about diet, this is usually what is meant by "vitamin D". Precalciferol: "Vitamin D1" - cannot be metabolized. Is produced and used by our body as part of the natural process of calcitriol production when exposed to UVB. Ergocalciferol: "Vitamin D2" - also referred to as calciferol which can mean ergocalciferol (D2) and/or cholecalciferol (D3). Is only found in plants. Is an evidence-based effective prohormone compound for producing calcitriol in the body. Cholecalciferol: "Vitamin D3" - also referred to as calciferol which can mean ergocalciferol (D2) and/or cholecalciferol (D3). Can be found in some plant-based foods. Is an evidence-based effective prohormone compound for producing calcitriol in the body. 22,23-dihydroergocalciferol: "Vitamin D4" - some evidence that it can be metabolized, but doesn't have as much supporting evidence as calciferol. Unfortunately there is no easily-readable widely-accepted name for this compound. Sitocalciferol: "Vitamin D5" - some evidence that it can be metabolized, but doesn't have as much supporting evidence as calciferol.