What’s the fuss?
Vitamin D is a liposoluble vitamin present in some foods, normally added to many others and also avaiable as a dietary supplement. It is also, primarily, produced in our own body when exposed to ultraviolet radiation.
For those who are not familiarized with the subject, liposoluble vitamins are, as it’s own name suggests, vitamins that are soluble in lipids (fat soluble) and not in water (hidrosoluble). This means that in order to be absorbed, these vitamins require, among others things, the presence of fat in our organism.
The vitamins classified as liposoluble are vitamins A, D, E and K. Vitamins A and D are primarily stored in the liver and vitamin E in the fat tissues and reproductive organs. Vitamin K is stored in very small amounts.
There are several diverse forms of Vitamin D (diverse chemical compositions with similar molecular structure, so to speak). The two main forms of vitamin D we normally refer to are D2 (ergocalciferol) and D3 (cholecalciferol). When we talk about vitamin D, we are normally talking about these two forms.
Vitamin D2 was chemically characterized in 1931, while D3 was established and accepted as the direct result of UV radiation in 1935.
Sun and stuff?
Not pretending to dig in chemistry (even more because I don’t have enough knowledge to do so), let’s try to simplify some things:
The chemical composition of vitamin D is slightly different from other vitamins. It is in fact classified as a liposoluble secosteroid (derived from cholesterol). No, vitamin D is not juice (anabolic steroids), but it in fact an extremely potent hormone, responsible for the absorption of calcium, iron, magnesium, phosphate and zinc. Despite being found in some foods and added to many others (as already refered above), the main natural source of vitamin D is, as has always been, the dermal synthesis, which depends on exposing our bare skin to sunlight (specifically to UVB radiation).
Either dietary vitamin D or the one synthesized through sunlight exposure is biologically active – requires an enzymatic conversion that takes place in the liver and kidneys. It looks that there is strong evidence that the synthesization of vitamin D via sunlight exposure is regulated in our organism to prevent toxicity. This means that, in theory, it is impossible to produce excess of vitamin D (1). In the other hand, due to the large amount of contradictory medical research related to cancer and UV radiation, it still very hard to say how much sunlight exposure is safe and necessary to attain optimal levels of vitamin D.
The discordance amongst the scientific community about the optimal levels of vitamin D has become more and more popular and controversial, with the authorities from some countries refering levels twice superior or inferior to the ones refered by the IOM (Institute Of Medicine)
Generally speaking, the recommendations are as follows:
- With at least bare arms and face, sunlight exposure between 10h00 and 14h00, in a warm sunny day (not very probable during the winter in most countries), with no application of sunscreen, should be enough to reach optimal levels of vitamin D if:
- Between 10 to 15 minutes – pale skin
- 20 minutes – dark skin
- 30 minutes – older people
It’s easy to understand that the indications are neither very specific nor very probable to happen in a huge part of the globe.
Dietary Reference Intakes
Traditionally the DRI for vitamin D has been based on the necessary amount to prevent diseases like osteomalacia or tickets, as the result of it’s deficiency. The problem is that if some recent research shows that higher levels helps to prevent a series of diseases (such as fibromyalgia, rheumatoid arthritis, rickets, multiple sclerosis or diabetes(2)), other research indicates that the long-term exposure to high levels could have the reverse effect(3) (4). Still, the toxicity seems to be always connected to the excessive consumption of dietary vitamin D.
Because of these findings, the ideal levels of calcifediol concentrated in the blood tends to vary between 80 and 100 nmol/L(2). In 2011 the IOM published a bibliographical review concluding that the optimal levels should be between 50 and 125 nmol/L (5).
It was also concluded that the DRI for vitamin D should be between 600 and 800IU (15 – 20ug), never under 400 or above 4000IU (10 – 100ug) (5).
DRI – by age:
Newborns | 0 – 12 months | 400IU
Infants | 1 – 8 years | 600IU
Youth and Adults | 9 – 70 years | 600IU
Elderly | >70 years | 800IU
Dietary sources of Vitamin D
The vast majority of vitamin D dietary sources are animal based. The most popular and known from it’s high concentration is blue fish (oily fish), like sardines, salmon, mackerel, tuna, amongst others(6). Besides fish, there are also avaiable many fortified foods, such as cow’s milk or eggs. The good news for those who do not consume animal products is that even vegetable milks or cereal are fortified nowadays.
One should consider the fact that a diet free of animal products will, almost certainly, be very poor in vitamin D. Perhaps even totally absent of.
There is also another factor to take into account – remember that I mentioned the difference between vitamin D2 and D3? Well, it happens that despite the fact of some research shows that vitamin D2 is equally effective mantaining serum 25-hydroxyvitamin D status (16), other papers show that vitamin D2 (ergocalciferol) seems to be less efficient than D3 (cholecalciferol) when it comes to raising calcifediol levels in the blood (7) (16). Nevertheless, as the paper itself indicates, it is still very complicated to get to a final conclusion.
VITAMINA D2 VS D3
Vitamin D2 is produced by some forms of plant life when exposed to UV radiation, which makes it a cheap source and, because of that, normally added to fortify foods.
Vitamin D3 is the most biologically active form of vitamin D, just found in humans and other animals. When the skin is exposed to sunlight, it converts the cholesterol in vitamin D3 (very simply speaking of course). You’re starting to understand the problem here right? Vitamin D3 is just produced by animals. Or is it? It looks like after all some forms of lichen also produce vitamin D3 (8) ! In other words, it is no longer impossible to find vegan vitamin D3 supplements. There aren’t many brands commercializing it, but there are some, like vitashine brand from Vegetology. Those of you who are vegan and do D3 supplement – unless the product has some sort of certification from The Vegan Society, or any other well known entity, it is highly probable that the supplement is made out of sheeps lanolin from it’s wool.
The Bone and the Sun Scene
Nothing in the human body depends on just one factor. This is why it is so important to know how to interpret essays, cohort studies, case control studies, etc. It is very easy to read a study and take foregone conclusions about it. But if you shouldn’t doubt science, you should question it.
Remember when I wrote about calcium, when I mentioned that several factors may compromise bone health, I even mentioned Norway’s example, with extremely high dietary calcium consumption and though with very high osteoporoses levels? Well, in this particular subject, vitamin D could perform a role just as if not more important than calcium itself (9).
When the calcium levels in the blood are low, parathormone (PTH) is released. PTH causes an accelerated release of bone calcium, thus lowering the calcium levels in blood. Osteoporoses could even be a result of chronic high levels of PTH. The conversion between calcifediol and calcitriol is also, on a certain level, regulated by PTH levels (10). The calcitriol increases the absorption of calcium and phosphorus (other of the bone main components) through the intestine and lower it’s excretion through urine. Because of this, the calcium levels in blood increase while the PTH levels lower
Vitamin D really is the f*ckin thing right?
So what’s the deal?
Ah, but I’m vegan ‘n stuff. Dude, you could even be cannibal, it would be the same sh*t. If your vitamin D levels are not optimal, you will most likely die soon (11).
Well, if you’re reading this and still can stand all my sh*t, from the three following options, you fit in two:
- you’re vegan, just like me;
- you like to have variety in your diet;
- you’re an idiot;
If you’re an idiot, there is not much I can do about it. You should have studied harder.
If you like to have variety in your diet, good for you. Still much better than comming here to tell me how healthy bacon is (12).
If you’re vegan and you’re worried about your vitamin D levels, well, before freaking out, do some blood tests.
Measuring the total serum 25(OH)D (25-hydroxycholecalciferol) seems to be the most viable option (17) .
Consider also the fact that responsible authorities, like theEndocrine Society, just recommend the test for at-risk pacients and not for the general population (18) . One of the reasons could be the “special and personal” character of this vitamin, the other could be the fact the the test result will vary quite depending on the method used in the lab.
In this study, the same sample was sent to over a 1000 labs around the world. The result was a variation of the total serum 25(OH)D levels between 20 nmol/L and 80 nmol/L (19) .
Well, if you managed to test your levels and they are low, I hope you’re getting some help from your doctor. Anyways, if that is the case, here is the deal my friend:
- either you start sunbathing;
- or you supplement with d2 or d3;
- or you go to the tanning salon;
If you live in a nice and warm place and you still go to the tanning salon… well… I don’t even know where to start. If so, apparently you’re on the right track if you want to increase your chances of skin cancer (13).
By this time I guess you’re wondering if you should do a vitamin D supplement. Well, as I already mentioned, some research seems to point D3 as a most efficient option when it comes to raise serum levels. However, the Endocrine Society recommends supplementing with either D3 or D2 to pacients in risk. In my opinion, if you’re already doing a D2 supplement and you don’t have any problem, I would say to stick with it.
Keep in mind that despite having some help with this post, I, personally, don’t have any relevant academic background and my personal analysis has it’s weight on what I write.
The truth is everything seems to indicate Equatorial Africa as the origin of our species. This means that back in the day we were all about running naked throughout the savanna, under the freshness of the african sunlight, before we decided to aventure ourselves in the rest of the globe, more than 50000 years go (14). When the homo sapiens had the urge of start having sexual intercourse with the neandertal and the denisovan, some adaptations to cold, altitude ‘n stuff were generated (15) .
Ahhh but a man can adapt to live anywhere, even cold as sh*t and with no sunlight. A man can adapt my ass! I know how all this rain all winter and summer makes me suffer. What I really mean is, despite the sunlight being essencial to all of us, probably because of all the mutations our species suffered, some of us are physically better adapted to live in cold and dark climates than others. I never read any scientific research regarind this, but I strongly believe our personal genetic code has something to do with the production of vitamin D. In my opinion, this could even help to explain how can countries with long hours of sunlight exposure (like Portugal for example) still struggle with vitamin D deficiency.
Well, by this time you should have learnt at least 2 things:
- If you’re racist, you’re stupid;
- If you live somewhere near the equator, just go more out’f*ckin’side man!;
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A very special thanks to nutricionist Margarida Guerreiro for reviewing all the material.
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