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Vitamin D is not a vitamin in the strict sense, but actually behaves like a hormone: it has thousands of receptors in the cells of the immune system and is the most important immunoregulator in our body.
Characteristics of vitamin D
There Vitamin D is fat-soluble, and it is a group made up of 5 different vitamins: Vitamin D1, D2, D3, D4 and D5.
From a metabolic standpoint, the most important are Vitamin D2 (ergocalciferol) and Vitamin D3 (cholecalciferol). The former is of plant origin, while the latter is of animal origin, but both have similar mechanisms of action.
Vitamin D and sun exposure
Our body is capable of synthesize vitamin D at the skin level, starting from cholesterol, thanks to the action of solar rays, in particular UVB rays.
20 minutes of sun is enough to synthesize all the vitamin D we need. However, it is not enough to expose only the wrists and face: at least 40% of our body surface must be exposed.
We also add that it's not true that the more we spend in the sun, the more we synthesize Vitamin D. After the first 20-30 minutes, in fact, we have already produced all the daily amount necessary for the well-being of our body.
In 20 minutes, our skin can synthesize 15 to 20,000 IU per day, but this process can be hampered by clouds and air pollution. Individual factors, such as skin color, age, and weight, can also play a role.
Vitamin D in foods
There are few foods that can be considered good sources of Vitamin D (liver, egg yolk, fish and, to a much lesser extent, also some mushrooms), for this reason it can be it is necessary to resort to supplements.
Vitamin D supplements: here's why you should take them
In this regard we would like to underline that it should be integrated every day and not in weekly or monthly doses.
The inactive form of vitamin D that we get through supplements (cholecalciferol) has a half-life of only 24 hoursThis means that if, for example, we take 20,000 IU all at once, the next day the body has 10,000 IU available, after 3 days 5,000, after 4 days 2,500 and so on until they disappear.
Daily Dosage of Vitamin D
As regards the daily dosage, recent research states that the recommended levels of vitamin D would seem to be too low for our daily needs and furthermore should take body weight into account.
For example, the required dose of vitamin D for those who are in overweight, would be around 12,000 – 20,000 IU per day, that is, an amount approximately 3 times higher than that needed by a normal weight individual and approximately 5 times higher than the maximum intake level currently recommended by many medical scientific societies.
In literature no cases of toxicity have been highlighted at dosages below 30,000 IU per day and with a blood level below 200 ng/ml.
There are some pathological conditions that, on the contrary, advise against supplementation at this dosage. These include: hypercalcemia, renal failure, primary hyperparathyroidism, and hyperthyroidism.
So it is always advisable monitor blood values such as calcemia, phosphatemia and parathyroid hormone even in healthy subjects, so that a targeted and personalized integration can be outlined.
When to take vitamin D?
There is no specific time, but it may help to take it early in the day (breakfast, or at lunch at the latest) on a full stomach, as it is a fat-soluble vitamin, which means it is absorbed in the presence of fats, especially saturated fats.
