Vitamin D: what is it used for?

Vitamin D, or calciferol, plays an essential role in the absorption of calcium in the body: it thus ensures bone growth and mineralization. It is also a valuable ally in strengthening our immune system. Where to find it? How to use it ? And for whom?

Often called the “sunshine vitamin”, vitamin D is essential for the proper functioning of our body. Its main role: “increase the absorption of calcium and phosphorus in the intestine and decrease their elimination in the urine, thus promoting the mineralization of bones and teeth”, explains Doctor Amar Medlkane, general practitioner at Louis Hospital Mourier in Colombes (92) and at COSEM Miromesnil (Paris 8th). This is why it is generally part of preventive treatments for osteoporosis, especially in women after menopause, as well as in the elderly.

Vitamin D: a key factor in immunity

Its role in the immune system is also underlined. “Vitamin D stimulates the immune system by acting on several varieties of immune cells belonging to white blood cells,” continues the doctor. With this in mind, certain studies confer on vitamin D a protective effect in the prevention and/or treatment of subjects infected with Covid 19. SARS-COV-2. But the evidence is insufficient to attribute the major role of vitamin D. Moreover, a drop in the concentration of vitamin D in an individual does not mean an increased risk of infection with Covid-19”.

Other studies also report effects on reducing the risk of cancer and the development of cardiovascular diseases. Again, solid studies are needed to confirm these trends.

The sun: the main source of vitamin D

If vitamin D is essential to our metabolism, unfortunately our body does not produce it. “This fat-soluble vitamin (soluble in fatty substances) exists in two forms, explains Dr. Medklane. On the one hand, vitamin D2 present in food, especially in plants. On the other, vitamin D3 synthesized in the skin by the action of ultraviolet rays”.

Indeed, exposure to the sun provides the body with a sufficient daily intake of vitamin D. Daily exposure of 15 to 20 minutes – if possible between 11 and 14 hours – is necessary. “Vitamin D is synthesized in the skin under the effect of the sun and more precisely UVB”, adds the general practitioner. The amount of vitamin D synthesized in the skin varies from one person to another because it depends in particular on age, skin pigmentation (dark-skinned people have higher vitamin D needs than fair-skinned people), the use or not of sunscreen (which would prevent the synthesis of vitamin D) and the duration of sun exposure. The rest of the intake is provided by food: mainly fatty fish (cod liver, salmon, sardines, mackerel, etc.), egg yolks and mushrooms.

Supplement in case of vitamin D insufficiency or deficiency

When the sun runs out, many people can more easily lack vitamin D. “We speak of vitamin D deficiency when its blood concentration drops below 12 nanograms per ml of blood, specifies the general practitioner. A vitamin D deficiency then leads to a drop in calcium in the body and therefore a lack of bone mineralization. It is she who is responsible in the long term for osteoporosis with risk of fracture. This risk is significantly greater in women after menopause. Vitamin D deficiency can also lead to weakening of the bones, called rickets in children and osteomalacia in adults.

If food and sunshine are not enough, a doctor can suggest vitamin D supplementation. This is particularly true in the event of zero or almost zero sun exposure, repeated falls regardless of age, proven osteoporosis, a disease favoring osteoporosis, a severe chronic pathology favoring insufficiency or deficiency such as obesity and in the elderly because of the risk of falls. “There is no proven interest in supplementing pregnant women, reassures the doctor. On the other hand, it is contraindicated in the presence of a high level of calcium in the body – whatever the cause – and kidney stones (lithiasis) associated with certain calcium pathologies”.

Vitamin D in children: use drugs and not food supplements

In children, vitamin D is essential for bone growth. “In France, vitamin D supplementation is recommended from the first days of life in order to prevent rickets and must be continued throughout the growth and bone mineralization phase, i.e. until the age of 18” , recalls the ANSM (the National Agency for the Safety of Medicines).

“We have alerted the health authorities that cases of vitamin D overdose have recently been reported in young children following the taking of food supplements enriched with vitamin D instead of medication, regrets Dr Andreas Werner, pediatrician and vice-president of the AFPA (French association of ambulatory paediatrics). There are real risks of overdose favored by high concentrations (500 to 10,000 IU of vitamin D in 1 drop) and by the absence of dose recommendations according to age”. These cases are manifested by hypercalcaemia (excessive level of calcium in the blood) which can have serious consequences, especially in the kidneys (kidney stone, calcium deposit in the kidney, etc.).

“The level of safety of vitamin D-based drugs (such as Adrigyl and Zyma D) is subject to regulatory requirements higher than those that apply to food supplements,” recalls the pediatrician. “They should therefore be given priority, especially in infants”.

For older children, after the first two years, it is possible to give these drugs during the fall/winter, when children are less exposed to the sun.