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Vitamin D for bones: why it is so important

Vitamin D for bones: why it is so important

The degenerative pathologies of the skeletal system can be very synthetically traced, at least from the point of view of an effective phytotherapeutic intervention, to the alterations of the calcium metabolism and to the substances related to it (phosphorus, silicon, fluorine and to the sterol group goes by the name of vitamin D).

Vitamin D deficiency is a widespread condition in the general population in different geographical areas, although this phenomenon is generally underestimated. Numerous experimental and clinical evidences show that vitamin D deficiency represents not only an important factor conditioning skeletal health, but also a possible contributing factor in the pathogenesis of numerous chronic diseases.

Although vitamin deficiency can be detected in all ages of life, it is the elderly population that is most frequently subjected to it. In fact, most of the vitamin production depends on sun exposure and only minimally on the amount taken with food, so that the categories most at risk of failure are those with limited exposure to sunlight and poor nutritional status. It is therefore clear that the elderly are the most exposed class to the harmful effects of vitamin deficiency, due to lifestyles and consequent lower ability to produce vitamin D.

What is vitamin D and where it is found

The term "vitamin D" refers to a group of five liposoluble pro-hormones of which, however, only two have physiological relevance: ergocalciferol (vitamin D2), which derives from ergosterol present in plants, and cholecalciferol (vitamin D3) produced from 7-dehydrocholesterol, present in the skin and precursor and derivative of cholesterol which, after absorbing UV light (solar radiation) undergoes a series of conformational changes and turns into provitamin D3, which is then converted into vitamin D3. However, as the years go by, the cutaneous capacity to produce cholecalciferol is reduced, which is one of the main reasons that particularly expose the elderly to the risk of developing a deficiency state.

Only 10% of vitamin D is supplied by the diet, the remaining 90% is produced in the skin thanks to exposure to the sun. Vitamin D is contained in an appreciable quantity only in a few foods of animal origin: cod liver, fatty fish fillet (herring, salmon), trout, fresh blue fish, in particular mackerel, whole milk, butter, some hard cheeses and eggs.

Vitamin D is absorbed in the intestine with the same modalities as other lipid substances present in food. In several tissues, including the liver, vitamin D is hydroxylated to 25-hydroxycholecalciferol and as such enters the bloodstream linked to a specific transport protein. At renal level 25-hydroxycholecalciferol is hydroxylated to 1,25-dihydroxycholecalciferol (the biologically active form of the vitamin) or to 24,25-dihydroxycholecalciferol (the inactive form of the protein). Low levels of calcium and / or phosphorus stimulate the synthesis of 1,25-dihydroxycholecalciferol, while high levels of calcium are that of 24,25-dihydroxycholecalciferol. Unlike other fat-soluble vitamins, vitamin D is not stored in the liver.

Why Vitamin D is so important?

Vitamin D:

- stimulates the intestinal absorption of calcium and phosphorus, the reabsorption of renal calcium and bone mineralization processes;

- is involved (in the form of 1,25 dihydroxycholecalciferol) in the regulation of cell proliferation and differentiation processes; in particular it seems to stimulate the differentiation of osteoclasts in bone and of keratinocytes in the epidermis;

- exerts an anti-proliferative action in different tissues including the epidermis and tumor cells in culture;

- in the form of 1,25-dihydroxycholecalciferol it binds to the receptor thus forming a complex that induces the biosynthesis of calcium transport proteins. Vitamin D-dependent calcium transport proteins are present in numerous body districts including the intestine, kidneys, skeleton. 1,25-dihydroxycholecalciferol, the active form of vitamin D, can be considered a hormone. Vitamin D regulates the metabolism of calcium in our body together with two other hormones: parathormone (PTH or parathyroid hormone, which mobilizes calcium from bones and increases urinary excretion of phosphate), calcitonin (better defined as thyrocalcitonin because it is secreted from parafollicular cells of the thyroid: lowers the blood level of calcium and phosphate and inhibits bone resorption).

It is also known that the absorption and utilization of calcium is influenced by the plasma levels of Ca (2+) and PO4 (2–) and by the presence of vitamins D3.

What factors could lead to vitamin D deficiency?

Plasma levels of 25-hydroxycholecalciferol less than 5 ng / l (or 12.5 nmoli / l) determine the appearance of deficiency symptoms. A lack of acquired vitamin D can depend on various factors:

- old age,

- malabsorption,

- lifestyle characterized by long days indoors, with poor exposure to the outdoors and therefore to the sun,

- kidney failure,

- anticonvulsants,

- inadequate intake of vitamin D with the diet,

- phototype (people with dark skin need more sun exposure than people with fair skin in order to produce vitamin D) and excessive use of sunscreen.

Vitamin D deficiency may also be due to hereditary disorders of vitamin D metabolism (1 alpha hydroxylase deficiency or vitamin D resistance to action)

What does vitamin D deficiency entail?

Vitamin D deficiency is associated with:

- the reduction of intestinal calcium absorption (there is a reduction in the serum concentration of calcium and phosphorus),

- increased parathyroid secretion (PTH) (secondary hyperparathyroidism and increase in serum alkaline phosphatase occur),

- increased bone turnover, osteoporosis, increased risk of femoral and non-femoral fractures.

In its most severe expression, vitamin D deficiency causes osteomalacia, rickets in children.

Furthermore, vitamin deficiency is associated with weakness and muscle pain, impaired physical performance, easy tendency to fall; the correlations existing between vitamin D and muscle activity are based on the evidence that muscles possess receptors for vitamin D.

The intake of high doses of vitamin D instead determines the increase in plasma levels of 25-hydroxycholecalciferol, while those of 1,25-dihydroxycholecalciferol remain unchanged. Plasma levels of 25-hydroxycholecalciferol higher than 100 ng / l (or 150 nmol / l) determine the appearance of signs of intoxication (nausea, vomiting, diarrhea, hypercalcemia, hypercalciuria, nephrocalcinosis and soft tissue calcification).

Difference between Osteoporosis, Osteomalacia, rickets

Osteoporosis is a disease due to excessive demineralization of the bone, which becomes very fragile and prone to fractures.
It is known that from birth onwards the skeleton grows and increases its heritage in terms of mineral density up to a maximum value (defined as "peak bone mass") around 30-35 years, up to 40 years is maintained a equilibrium condition between bone resorption and neo apposition, then the mineral density of the skeleton starts to decrease slowly.At the time of menopause, in women the loss of bone happens much more quickly, because the ovaries are no longer able to produce estrogen, very important hormones for maintaining the balance of the skeleton.The deficiency of estrogen favors bone resorption at the expense of neoformation, so that bone mineral density undergoes a significant decrease.In man, this process is slower and more linear, but progresses with age, so that both sexes at a later age are at risk of osteoporosis.

Osteomalacia is a skeletal disease characterized by a defective mineralization, with accumulation in the non-mineralized matrix bone (osteoid). The bone thus formed is weaker and softer than normal and undergoes deformations with the load (eg curved legs). The term osteomalacia refers to the disease of the adult, which develops after the end of growth. The most frequent form of osteomalacia is due to a deficiency of vitamin D, which can be determined by reduced production in the body, malabsorption, liver disease, chronic anticonvulsant therapies. Less frequent are the osteomalacie due to altered metabolism of vitamin D, resistance to the action of vitamin D, hypophosphatemia and hypophosphatasia.

The term rickets is used instead for the still growing skeleton, in which the mineralization defect concerns both the bone and the epiphyseal cartilage.

Recommended levels of vitamin D intake

Under normal conditions, exposure to sunlight is sufficient to meet the body's need for vitamin D. The scientific societies SIOMMMS (Italian Society of Osteoporosis, Metabolism Mineral and Skeletal Diseases), ES (Endocrine Society) and AGS (American Geriatric Society) define optimal serum levels of vitamin D ≥30ng / mL, considering lower values ​​conditions of lack / insufficiency. They also suggest the preventive intake of vitamin D in some sections of the population, the elderly and post-menopausal women, regardless of clinical conditions and knowledge of serum levels. On the contrary, the threshold indicated by the US NAM and the British National Osteoporosis Society (NOS) to define the safe deficiency has been placed below 10ng / mL, while below the 20ng / mL a "risk of inadequacy" is identified .

What do you recommend for bone maintenance?

Two supplements, to be chosen based on the need and practicality of us

The classic cod liver oil, in pearls (liquid would be too unpleasant, so instead it is tasteless!), Rich in vitamin D, of animal origin, is generally recommended for a harmonious body development and also used in prophylaxis of rickets in children, in osteoporosis in adults.

FitoD3, contributes to the normal maintenance of bones and to the absorption of calcium and phosphorus and to the normal functionality of the immune system. More recommended than cod liver oil if you already have a problem due to vitamin D deficiency. Covers a 2 month treatment.

FitoD3 is in liquid form (in oil) because it is sensitive to water (it oxidizes in contact) and sensitive to heat (if compressed it is heated during processing). FitoD3 is natural, of vegetable origin (not animal!) As it is extracted from Icelandic lichen, therefore also suitable for vegans. It is palatable having a citrus flavor.

How to take FitoD3? From 3 to 10 years: 4 drops per day. Boys, pregnant and lactating women: 6 drops per day. Adults: 20 drops per day. Do not exceed the recommended daily dose.

Dr. Laura Comollo

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