OUR HEALTH ADVICE – Essential for the good health of our bones and muscles, this vitamin is mainly provided by the sun. But diet also plays a big role. Here is the recipe to ensure an optimal intake.
Save who can, winter is here. The sun is lacking and, with it, vitamin D. In fact, it is essentially synthesized by the body through the exposure of our skin to ultraviolet rays (UVB). This fat-soluble vitamin, which is fixed in fat, comes for 30% from food and for 70% from sun exposure. And this, on the condition of offering for 20 minutes a day the equivalent of 30% of the surface of the body to zenithal rays, without filtering sunscreen or atmospheric pollution, which blocks ultraviolet rays.
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In our latitudes, between October and April, we produce very little vitamin D. As a result, “80% of French people have a deficit”, declares the Dr Jean-Michel Lecerf, head of the nutrition department at the Institut Pasteur de Lille. Certain categories of the population are even more likely than others to be deficient, like people with dull or dark pigmentation, as well as elderly subjects whose skin synthesis is less efficient. This is why they are advised to go out regularly and take advantage of the slightest sunshine, taking care to uncover their forearms, hands and face.
A protective role
Vitamin D plays an essential role in the mineralization and maintenance of bone capital, by promoting the intestinal absorption of calcium. “It is a protective factor against rickets, one of the major growth disorders in children, against osteomalacia, or soft bone disease, generally coupled with bone pain, muscle weakness and fatigue, especially in young women with multiple and closely spaced pregnancies, and against senile osteoporosis, which increases the risk of fractures”, indicates Marie-Christine Boutron-Ruault, doctor and director at the National Institute of Health and Medical Research (Inserm).
Is this its only function? Several epidemiological studies have highlighted that vitamin D deficiencies are associated with an increased risk of breast, colon and prostate cancers, cardiovascular diseases, neurodegenerative pathologies or even macular degeneration linked to age (AMD). “If this vitamin is, in fact, a hormone and that vitamin D receptors are present in a very large number of cells in the body, interventional studies nevertheless struggle to provide definitive proof”, note the Dr Jean-Michel Lecerf.
A new lead could however emerge: the potential immunomodulatory effect of vitamin D, highlighted in the current epidemic context, in particular during the first wave of Covid-19 which was accompanied by strict confinement. “The first observational studies showed that more than 80% of severe forms of Covid-19 affected patients who were deficient in vitamin D (1)”summarizes the Dr Boutron-Ruault. More than fifty international clinical studies are underway to assess the effectiveness of vitamin D in the treatment and prevention of SARS-CoV-2 infection. In the immediate future, and this was the meaning of the notice published on April 17, 2020 by the National Health Security Agency (Anses) which invited the French to “ensure adequate intake of vitamin D through diet», we must not neglect to consume it. This contribution weighs for less than a third, but it counts, especially in periods when the UV index is close to zero.
Prioritize fortified dairy products
“There are two kinds of dietary vitamin D: vitamin D2 (ergocalciferol) which is of plant origin, and vitamin D3 (cholecalciferol) which is found in animal products. Both are useful, but vitamin D3, which is also the one synthesized during sun exposure, is a bit superior, because it contributes to more effectively increase the blood level of 25-hydroxyvitamin D (25-OHD), a form under which vitamin D is stored in the body”explains the Dr The deer. “The main sources, for adults as well as for the child, are dairy products, especially those enriched with vitamin D, says Gwenn Vo Van-Regnault, Nutrivigilance Project Manager at ANSES. Then come fatty fish, limited to one portion per week, then offal, especially liver, egg yolk, fat or even certain mushrooms, the only vegetables to contain it.
Cod liver oil remains unbeatable, even if it is not very tasty! Otherwise, it is better to favor small oily fish (sardines, mackerel, etc.), which are less contaminated by heavy metals than fish at the end of the chain (tuna, salmon, etc.). They are also less expensive. “But families do not spontaneously turn to these products when they want to treat themselves”, notes the Inserm research director. Not to mention the diets that then advocate the reduction of foods of animal origin, such as veganism.
This is why medicinal supplementation, always based on vitamin D3, may prove to be essential in order to achieve the correct doses throughout life. During childhood and in old age, daily needs are greater. The recommended daily intakes are 400 to 800 international units (IU) for healthy children, and 800 to 1000 IU for seniors. A daily prescription is also recommended for the prevention of fractures and falls. It is preferable to a monthly prescription of around 50,000 IU, even if the latter still gives good results. “In contrast, taking mega-doses every 6 or 12 months did not show positive effects”, warns Jean-Michel Lecerf. Supplementation must be checked and discussed with your attending physician, in order to avoid the risk of hypervitaminosis. It is also necessary to ban food supplements overdosed in vitamin D, available in free access. “This vitamin remains a hormoneinsists the Dr Boutron-Ruault, and work would tend to show that there is no interest in taking doses higher than our needs and that this could even be pathogenic.” Finally, to facilitate its assimilation, it is preferable to ingest this fat-soluble vitamin during a meal rich in fat.
(1) Journal of Endocrinological Investigation, June 2021; European Review for Medical and Medical Sciences, February 2021; Journal of Internal Medicine, January 2021; Nutrients, November, 2020.
3 questions to… Gwenn Vo Van-Regnault
Gwenn Vo Van-Regnault is in charge of the nutrivigilance mission at the National Agency for Food, Environmental and Occupational Health Safety (ANSES).
“Beware of overdose in infants”
Why has ANSES issued an alert on the risk of overdose in toddlers?
Gwenn Vo VAN-REGNAULT. – ANSES received three reports. In all three cases, the parents of the newborns had a medical prescription for drug supplementation, with a well-defined dosage. This supplementation has been replaced by food supplements. The three products, purchased on the internet, and intended for adults, had doses up to 30 to 40 times higher than the recommendations issued for children.
What are the risks?
The main consequence is hypercalcemia. An overdose of vitamin D leads to an increase in calcium in the blood, which initially results in a loss of appetite and weight, vomiting, digestive disorders… But, depending on the case, this can cause heart damage. , with arrhythmias, and/or kidney damage, with calcification in the kidneys, or even life-threatening infants.
What forms should be favored for infants?
The drug should be preferred to avoid any risk of overdose. Unlike food supplements, it is subject to supervised and validated trials. The sources of vitamin D intake should not be multiplied, as this increases the risk of overdose, and the purchase of food supplements on the internet should be avoided, due to the risk of non-compliance.
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10 and 15 μg
This is the recommended dietary intake of vitamin D per day: 10 micrograms for children 0-18 years old, without risk factors, 15 for healthy adults, and up to 20-25 μg for the elderly at risk.
The main food sources
Foods rich in vitamin D are few in number and mostly come from the sea. The guidelines that follow do not take into account fortified margarines, milks or yoghurts, which provide valuable support for consolidating one’s needs.
Cod liver oil 250 μg/100 g
Raw cod liver 100 μg/100 g
Horse mackerel 48.5 μg/100 g
Sardine, pilchard, swordfish, herring, anchovies, eel, rainbow trout 10-20 μg/100 g
Mackerel, tuna, margarine 7-9 μg/100 g
Veal liver, bacon, egg yolk, shiitake, morels, porcini mushrooms, dark chocolate 2-6 μg/100 g
Emmental, soft cheese, milk, butter, mozzarella, yoghurt 0.2-1.5 μg/100 g
Source: Ciqual table, 2020
At the end of winter, stocks are at their lowest
Between the synthesis of vitamin D, under the effect of ultraviolet rays, and its use by the body, there is a lag. “In summer, generally, we fill up and, therefore, reserves on which we will live until the beginning of wintersays Jean-Michel Lecerf. When we come to spring, we’re totally flat.” “This is whycontinues Marie-Christine Boutron-Ruault, that our stocks are at the top between July and September, the time in May-June to start recharging the batteries.” Hence a drug supplementation most often prescribed on the threshold of autumn. Hence also the importance of a good daily food intake.
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Serum vitamin D assay
The serum dosage of vitamin D (25-OH-vitamin) is no longer supported, except in certain indications: obesity, intestinal absorption problem, kidney transplant… The normal values of a dosage of 25 -OH-vitamin D3 in plasma oscillate between 30 and 45 nanograms per milliliter.