Table of Contents
Vitamin D and sun
The term vitamin D refers to both vitamin D2 than vitamin D3, both of which are present in some foods and food supplements. These are inactive forms that are converted into calcitriol after passing through the liver and kidneys. The calcitriol is the physiologically active vitamin D.
Although food can be a source of this precious vitamin, it must be said that most of it is produced by our own body when we expose ourselves to the sun. Penetrating into the skin, ultraviolet rays trigger the synthesis of vitamin D starting from an intermediate of the cholesterol metabolism. In temperate latitudes, when a skin surface equal to that of the forearms is exposed for about a quarter of an hour being careful not to wear sunscreen, 80% of the vitamin comes from hers skin synthesis and the remaining 20% from food.
There history of vitamin D it begins in the first twenty years of the last century when it was discovered that children with rickets recovered when exposed to sunlight. At the same time it was found in thefish liver oil a fat-soluble compound essential for bone metabolism. It was the same substance responsible for healing children. The structure of vitamin D was definitively identified in 1930 by Windaus.
What is it for?
Vitamin D mainly has one skeletal function since it maintains the balance between calcium and phosphorus and makes it possible tooptimal bone mineralization. We must not forget, however, that vitamin D is also able to interact with specific receptors present within the nucleus (they are indicated with the abbreviation VDR) in order to favor the expression of some genes. Through this modality Vitamin D can exercise a variety of extra-skeletal effects.
The main functions of vitamin D can be summarized as follows:
- Absorption of calcium and phosphorus in the intestine;
- Maintaining normal blood calcium levels;
- Adequate bone mineralization for the health of our skeleton and teeth;
- Stimulus to protein synthesis and to muscle contraction;
- Promotion of the biosynthesis and release of insulin by the cells of the pancreas that have this role;
- Increased insulin sensitivity e diabetes prevention food;
- Anti-inflammatory action;
- Increased immunity innate against different infections (tuberculosis, flu, viral infections of the upper respiratory tract).
Since it acts simultaneously on both the skeleton and the skeletal muscle, enhancing both of them, vitamin D seems to be the vitamin of all those who practice outdoor sports. While the skeleton becomes stronger by virtue of the mineralization of the bone matrix, the muscles are also strengthened by the boost that vitamin D exerts on the synthesis of muscle proteins.
What happens, however, to those who are sitting behind a desk all day? The light that penetrates through the window panes does not have such an intensity as to initiate the synthesis of vitamin D in the skin. Sitting behind a desk all day long gets lost bone mineral density and muscle mass at the same time, unless it is compensated by physical activity and adequate supplementation, especially in the winter months.
Vitamin D deficiency
The synthesis of vitamin D is affected by several factors. Some have to do with the characteristics of the individual, others with the environment. As we age, the mechanisms of synthesis of vitamin D in the skin become less and less efficient. For this reason the seniors are among the people at greatest risk to meet a deficiency state.
In general we could say that the vitamin D deficiency it is determined in most cases by a reduced exposure to sunlight and only secondarily by an insufficient intake with the diet. To determine if we are deficient in vitamin D it is necessary measure blood concentration of an intermediate referred to as vitamin 25 (OH) D. There is talk of deficiency for a value of 25 (OH) D equal to or less than 20 picograms per milliliter. There severity vitamin D deficiency is certainly higher during the winter months when exposure to sunlight of adequate intensity is a rare event.
Furthermore, since vitamin D is fat-soluble (i.e. it dissolves in fat) it tends to settle in the adipose tissue being somehow kidnapped. It is therefore understandable why subjects with an overweight or obese condition need greater intakes of vitamin D with the diet compared to normal weight in order to reach adequate plasma levels.
Vitamin D deficiency has several adverse effects on our health, first of all determining a reduction in the concentration of calcium and phosphorus in the blood. Secondly to this first event, an inadequate mineralization of the skeleton is observed which manifests itself as rickets in children and as osteomalacia (ed. a pathology caused by insufficient quantities of minerals, which make the skeleton susceptible to fractures, malformations and pains) and osteoporosis in adults. The weakened bones undergo deformation as you begin to feel severe skeletal pain. If, in addition to being deficient in vitamin D, we also consume a diet low in calcium, the clinical manifestations will be even more serious. Some studies document how a vitamin D and calcium supplementation can in the elderly significantly reduce the risk of fractures, especially those involving the hip and lumbar vertebrae.
Since, as we have seen, vitamin D also plays an important role in the health of our muscles, the condition of deficiency is associated with muscle fatigue it’s at strength reduction. More tired and lacking in strength muscles can lead to the appearance of balance disorders. We could therefore say that the two most important risk factors for accidental fall fractures (bone demineralization and loss of balance) can both result from a vitamin D deficiency.
In which foods it is found
In order to reach adequate blood levels it is useful to know which foods contain vitamin D. The best sources include:
- the fatty fish such as trout, salmon, tuna and mackerel;
- L’Cod liver oil, which provides a significant amount and has been used for a long time to treat deficiency states;
- more modest quantities are contained in beef liver, in milk, butter, cheese and in the egg yolk.
The plant-based foods they are almost completely devoid of vitamin D: i mushrooms, to which we are unaccustomed to attribute a nutritional value, are a decent source of vitamin D2. Finally, they are on the market enriched products with vitamin D. Milk, yogurt, vegetable drinks and breakfast cereals are among the main foods fortified with the addition of this vitamin.
Read also
