Sunny Vitamin. What scientists hide
Vitamin D is conditionally assigned to the group of vitamins, in fact it is a fat-soluble prohormonal steroid that is involved in endocrine, paracrine and autocrine regulation [Vanchinathan, Lim 2012].
Synthesis of Vitamin D in the Skin
According to the International Lighting Engineering Commission (MSC), effective radiation (i.e., the effectiveness of each wavelength for the synthesis of vitamin D in the skin) covers the spectral range of 255–330 nm with a maximum of about 295 nm (UVB). Exposure to UV light, which induces redness of the skin at a minimum erythema dose for 15–20 minutes, can induce the production of up to 250 μg of vitamin D (10,000 IU) [Krause et al. 1998, Stamp et al. 1977].
The precursor of vitamin D in the plasma membrane of basal and suprabasal keratinocytes and dermal fibroblasts 7-dehydrocholesterol is converted to provitamin-D3. Vitamin D3 synthesized in the skin is released from the membrane and enters the systemic circulation associated with vitamin D-binding protein (DBP) [Clemens et al. 1982].
Once in the bloodstream, vitamin D is converted in the liver by the action of hydroxylase to 25-hydroxyvitamin 25 (OH) D, or calcidiol. A circulating 25 (OH) D level is a measure of vitamin D content. This level reflects the dose of ultraviolet radiation and vitamin D intake from food.
Sources of Vitamin D
[by: Vanchinathan, Lim 2012; Kochupillai 2008; Gilchrest 2008]
But why – may an attentive reader ask – so many scientific references, because everything is obvious and so? Everything can be learned from any glossy magazine or beauty blog.
If you are sure, then you can stop loading yourself with unnecessary reasoning, and we will try.
We at the editorial office selected some of the most enduring conflicting myths and looked for answers from scientists.
Vitamin D Myths
Myth 1. Vitamin D is synthesized in adequate quantities only if you consume a lot of animal protein and drink milk.
A number of respected authors claim [LoPiccolo, Lim 2010; Holick et al. 2011] that there are only a few natural sources of vitamin D:
fish (mackerel, salmon, tuna)
Since it’s not easy for many people to get enough vitamin D from natural food sources, many countries consume foods such as orange juice, milk, yogurt, and cereal with vitamin D.
Colin Campbell, the author of the acclaimed “Chinese study”, on the contrary, claims that the use of animal protein for a long time usually blocks the production of vitamin D and as a result reduces its concentration in the blood. Moreover, the long ingestion of large amounts of calcium creates favorable conditions for the reduction of “superpowerful vitamin D” in the body.
We are not yet aware of the situation with the “powerful” vitamin, but we see a powerful contradiction.
Norwegian scientists come to the rescue, who have proved and shown that sailors who eat a lot of fish but drink a little milk have excellent vitamin D values, even in short sunlight.
Conclusion: it is very important that the influence of nutrition is carried out through a thin chain of biochemical interactions. In a debate about animal or vegetable protein, doctors need to look at both vitamin D and calcium levels.
Vitamin D deficiency can occur with:
his lack of diet for some time
limited exposure to sunlight
impaired renal function of the conversion of 25 (OH) D into an active form of insufficient absorption of vitamin D in the digestive tract.
Myth 2. Prescribing high dosages of vitamin D is safe.
Vitamin D is produced in the skin, then transferred to the liver, where, under the influence of enzymes, it is transformed into a metabolite of vitamin D (while it is mainly in the liver and in fat).
The next step is key. If necessary, some of this vitamin is transported to the kidneys, where, under the influence of another enzyme, it is converted to a metabolite of 1.25 D. The main thing in this process is the speed with which vitamin D is converted in the form of reserves.
The activity of 1.25 D is approximately 1000 times higher than that of vitamin D in the form of reserves, and it persists for 6–8 hours after production.
For comparison: vitamin D in the form of reserves is stored for 20 days or more.
This is how any finely organized system works: the higher the activity, the shorter the validity period and the lower the quantity of the final product.
A curious observation was provided by McCullough P. J and colleagues (2019). We quote: “All patients in our hospital regularly (starting from July 2011) were tested for vitamin D, and depending on the results, they were offered supplements to regulate the level of vitamin (to reduce or increase it). During this period, we observed over 4700 patients, most of them agreed to a dose of vitamin D at 5000 or 10,000 IUs / day.
Due to illness, some patients agreed to a dose increase of 20,000 to 50,000 IUs / day.