Why we need it
Vitamin D is vital for bone health. Additionally, it increases intestinal absorption of both calcium and phosphate substantially and maintains normal blood levels of these as well.
There are more recent studies investigating and highlighting how vitamin D affects other bodily functions such as immune function and endothelial function. Additionally, there is active research being conducted to investigate links between vitamin D deficiency and various metabolic and cardiovascular diseases… and even Covid-19!
Sources
Vitamin D can be synthesized in the human skin upon exposure to sunlight ( Ultraviolet B radiation to be specific). This version is known as vitamin D3 (cholecalciferol). It can also be obtained through the diet either as vitamin D3 or vitamin D2 (ergocalciferol), which is derived from plant sources.
Example food sources include:
- Fatty fish ( salmon, mackerel, sardines, cod liver oil) -D3
- Some types of mushrooms ( e.g. Shiitake) -D2
- Fortified foods
- Vitamin D supplements
How much do we need?
As per usual, there are differences in vitamin D recommendations by the US, UK and FAO. Adults (both male and female of all ages) should get around 400-600 IU daily (International Units, 200 IU= 5µg). In case you’re curious, 400IU is the UK recommendation and 600IU is the US recommendation. However, these numbers are only useful if you plan on getting your vitamin D from the diet. According to the FAO, in most cases, approximately 30 minutes of sun exposure to the face and arms can provide the daily requirements of vitamin D.
Factors affecting Vitamin D Synthesis
- Geography (latitude and season) – the amount of UV light reaching the skin at the equator will be much greater than say… in Iceland
- Ageing- thinning of the skin reduces the efficiency of synthesis
- Skin pigmentation- darker skin pigments affects how far UV light can travel into the skin
- Clothing- reduces light reaching the skin
- Sunscreen use- Perhaps a bit contentious… although sunscreen helps to protect the skin from damage, it also negatively affects vitamin D synthesis
Storage
A super quick note on storage… Vitamin D is fat-soluble and so it can be stored in adipose tissue.
References
- Vitamin D and Covid-19
- Vitamin D: Deficiency, Sufficiency and Toxicity
- Harvard: The Nutrition Source: Vitamin D
- Vitamin D and Endothelial Function
- Vitamin D and Immune Function
- Vitamin and mineral requirements in human nutrition, 2nd edition (WHO + FAO 2004)
- Nutrition Requirements by the British Nutrition Foundation(2019)
- Dietary Guidelines for Americans (2020-2025)
I try to make these posts as brief and as concise as possible. For further detail, feel free to check out the references above!
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