Since ancient times, sunlight has been recognized as an essential source for human health. In particular, when there is a lack of vitamin D, it is common for doctors to suggest something as natural as exposing oneself to sunlight to obtain new doses of this precious vitamin, so we think that we get vitamin D from sunlight, although this thought is incorrect, so it is a new myth to dismantle, or at least to clarify, since the statement is not entirely correct.
But before we continue debunking the myth that sunlight carries vitamin D...
What is light?
In the article on electromagnetic waves, we discussed two aspects of light, the first, that it is an electromagnetic wave, and the second, that we will have its own article on the nature of light in Science Driven.
That article will come, but in the meantime, it is necessary to explain a concept in order to continue with this new installment of "Debunking Myths".
Light has been shown to comply with the electromagnetic theory as we discussed, but also with the corpuscular theory. This is known in physics as the duality of light and what it means is that light behaves at the same time as an electromagnetic wave and as a particle, two concepts that are incompatible with each other a priori, since electromagnetic waves cannot transport particles.
Physics has shown us that in the case of light it is possible, since as an electromagnetic wave, it meets all the requirements to be such, and experiments demonstrate this, but it also meets all the requirements to be composed of photons.
In any case, according to both theories, what it never transports is anything other than electromagnetic energy or photons, so it cannot transport any type of organic or inorganic element, which means that it does not transport vitamin D either.
So why do they tell us to sunbathe to recover vitamin D?
If at this point in your reading you are feeling that we have been deceived all our lives when we are told to sunbathe to compensate for our lack of vitamin D, the answer is NO, the health personnel have done the right thing.
It is wrong to think that vitamin D is received from the sun, and I will explain why.
The human body does not receive vitamin D through the skin due to the incidence of sunlight, the human body THANKS to sunlight, stimulates the production of vitamin D.
The process by which the human body generates vitamin D when stimulated by sunlight on the skin is a fascinating example of how the body interacts with the environment to produce essential nutrients. Vitamin D is unique in that it can be synthesized by the human body through exposure to ultraviolet B (UVB) light from the sun. Here's a detailed explanation of how this process occurs:
1. Skin exposure to sunlight
When human skin is exposed to sunlight, specifically ultraviolet B (UVB) rays of wavelength between 290-315 nm, the first phase of vitamin D synthesis begins. These UVB rays penetrate the upper layers of the skin, mainly the epidermis, where they interact with a precursor substance called 7-dehydrocholesterol, a compound that is abundantly present in the skin, in the cells of the epidermis. This compound is synthesized from cholesterol through a series of enzymatic reactions that occur in the liver and other parts of the body. In essence, cholesterol is transformed into 7-dehydrocholesterol by the action of enzymes during sterol biosynthesis.
2. Conversion of 7-dehydrocholesterol into previtamin D3
7-Dehydrocholesterol is a precursor to vitamin D found in the skin, and when exposed to UVB light, its molecular structure changes. The energy from UVB rays causes this compound to undergo a chemical transformation into an unstable molecule called previtamin D3. This step is crucial, as it converts an inert compound into an active precursor that the body can further transform.
3. Thermal isomerization: formation of vitamin D3
Once 7-dehydrocholesterol has been converted to previtamin D3, this molecule undergoes a process called thermal isomerization. This process occurs spontaneously under the influence of body heat. During isomerization, the structure of previtamin D3 is rearranged to form vitamin D3 (cholecalciferol), the active form of vitamin D that can be used by the body.
Vitamin D3, at this stage, is not yet fully activated, but is already in a useful form that can be transported to other parts of the body for further processing.
4. Transport to the liver
Newly synthesized vitamin D3 in the skin is transported by the blood to the liver. At this stage, a specific carrier protein known as vitamin D binding protein (DBP) binds to vitamin D3 and transports it to the liver, where the next stage of its activation occurs.
5. Hydroxylation in the liver: formation of 25-hydroxyvitamin D
In the liver, vitamin D3 undergoes a further transformation through a process called hydroxylation, in which an enzyme called 25-hydroxylase adds a hydroxyl group (-OH) to the vitamin D3 molecule. This reaction converts vitamin D3 into 25-hydroxyvitamin D [25(OH)D], also known as calcidiol.
25(OH)D is the main circulating form of vitamin D in the body and is the one measured in blood tests to determine if a person has adequate vitamin D levels. Although it is more stable than vitamin D3, it is still not the fully active form of the vitamin.
6. Transport to the kidneys: final activation
From the liver, 25-hydroxyvitamin D travels in the blood to the kidneys. Here, a second enzyme, called 1-alpha-hydroxylase, performs a further hydroxylation, adding another hydroxyl group to the 25(OH)D. This process converts 25-hydroxyvitamin D to 1,25-dihydroxyvitamin D [1,25(OH)2D], also known as calcitriol, which is the biologically active form of vitamin D.
Calcitriol is the molecule that the body uses to carry out most of the functions related to vitamin D.
7. Actions of calcitriol (1,25-dihydroxyvitamin D)
Calcitriol is the fully active form of vitamin D, and once it is produced in the kidneys, it is released into the bloodstream, where it binds to vitamin D receptors in different tissues of the body, and performs several essential functions:
- Calcium and phosphorus regulation : Calcitriol increases the gut's ability to absorb calcium and phosphorus from food, minerals that are essential for the formation and maintenance of healthy bones and teeth. Without enough active vitamin D, the body cannot maintain adequate levels of these minerals, which can lead to bone disease.
- Maintaining bone health : By increasing the absorption of calcium and phosphorus and mobilizing these mineral reserves into the bones, calcitriol helps maintain strong bones and prevent diseases such as osteomalacia in adults and rickets in children.
- Modulation of the immune system : Calcitriol also plays an important role in regulating the immune system, helping the body defend itself against infections and controlling inflammatory responses.
- Cellular Function : Active vitamin D also has effects on cell growth and differentiation, meaning it helps regulate the way cells grow, reproduce, and die. This is especially important in preventing certain types of cancer.
Curiosities about vitamin D synthesis
- People living at latitudes farther from the equator receive less UVB radiation, especially during the winter months, which can limit vitamin D production.
- Vitamin D production is most efficient when the sun is at its highest point (around noon), as the atmosphere filters less UVB rays.
- People with darker skin have more melanin, a pigment that protects against sun damage but also reduces the skin's ability to produce vitamin D.
- Although sunscreen is essential to prevent skin damage from the sun, it also blocks UVB radiation and can reduce vitamin D synthesis.
Conclusion
Although your doctor is right in ordering you to expose yourself to sunlight when you need vitamin D, it is not correct to think that vitamin D is transported in sunlight, but that sunlight is necessary to trigger all the physical reactions that cause the body to produce vitamin D.
And the article is over :(
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