Talk:Vitamin D

Do μg and IU refer to D3?
Vitamin D is a group of secosteroids. Amounts in IU and μg and given throughout the article, but I only see one case that states which form it refers to (D3). At a guess they're all D3 but this should be explicit. According to this https://walrus.com/questions/converting-micrograms-mcg-of-calcitriol-to-international-units one IU of D3 is equivalent to one IU of D2, but it makes no sense to talk about an IU of calcitriol as no amount of it can be said to be equivalent to one IU of D3. The URL above does not look like a citable reference, despite looking very scholarly, so I won't edit the article, but someone more knowledgeable might want to, to say something like "all references to IU are to D3" and something similar for μg if that's true. Housecarl (talk) 00:31, 9 December 2023 (UTC)


 * - New talk topics go to the bottom of the page, WP:TALK. This section of the article explains thoroughly the relationship between μg and IU for D3 and D2 food or supplement sources, which do not distinguish a possible difference in vitamin D production between the two substrates. Calcitriol is not expressed in the article in units of μg or IU. Zefr (talk) 17:28, 9 December 2023 (UTC)


 * My point was "Vitamin D" is a group of things and the quantities given do not identity which of those things they refer to. But now I see the Types section says "Vitamin D without a subscript refers to either D2 or D3, or both, and is known collectively as calciferol.[citation needed]". Housecarl (talk) 21:36, 9 December 2023 (UTC)

Production from sunlight
I What to add this two sections Production from sunlight and Absorption in the body from the sun. I have tried after best ability to follow WP:MEDRS.

To convey the difficulties, with getting vitamin D from the sun. And that getting vitamin D from sun/previtamin D is a different from supplement.

Production from sunlight


To produce Vitamin D, UVB light is required. To have sufficient light containing UVB, the UV index needs to be 3 or higher (≥45 solar zenith angle at sea level). Vitamin D production is maximal at one-third of the minimal erythemal dose. When UV exposure increases to a minimal erythemal dose, vitamin D synthesis stops. One must be south of latitude 50°N to produce vitamin D around the Winter solstice.

The table assumes that one is outdoors in sunlight for more than 3 times a week, wearing only swim trunks and a t-shirt or swimsuit, and has not applied sunscreen. Such exposure to the entire skin surface corresponds to receiving between 250–1250 μg of vitamin D (10k to 50k IU) per session, or a similar amount as obtained by consuming 125–500 ml of cod liver oil (200μg/100ml ).

The "summer level" decreases to "winter level" within 6 to 8 weeks after insufficient sun exposure, without supplementation.

Barriers to UVB absorption:

 * Sunscreen
 * Clothing covering a larger area
 * Overcast skies
 * Staying in the shade
 * Insufficient UV index.

Absorption in the body from the sun
Vitamin D absorption from sunlight differs from absorption from supplements. When absorbing 3 minimum erythema doses (the time it takes for the skin to turn red), with the whole body exposed to UV light:


 * Within 24 hours, serum vitamin D levels rose from 15 nmol/l to 149 nmol/l.
 * After 1 week, serum vitamin D fell back to its initial value, while serum 1,25-(OH)2-D reached its peak.
 * Between 2-3 weeks, serum 25-OH-D concentration reached its highest level, while serum 1,25-(OH)2-D fell back to its initial value.

The study does not mention the time it takes for serum 25-OH-D to return to its initial value.

In another study comparing the difference between 1 MED, 625μg D2 (25k IU) supplement, and 250μg D2 (10k IU) supplement  , they found that vitamin D from the sun lasts significantly longer than supplements. Vitamin D from supplements returned to baseline levels within 2 days, whereas vitamin D from the sun returned after 7 days. EidenNor (talk) 08:02, 24 April 2024 (UTC)