Dietary supplements

Vitamin D: what are the risks in the event of a deficiency?

For healthy people, we speak ofvitamin D deficiency when the blood concentration drops below 20 nanograms (20 billionths of a gram) per ml of blood. “All the experts consider that this is a correct minimum”, confirms Professor Jean-Claude Souberbielle, researcher at the Necker hospital in Paris.

We are talking about vitamin D deficiency when this concentration drops below 10-12 nanograms per ml of blood. But it is much rarer and mostly affects very old people who have diseases such as kidney failure.

Vitamin D, essential for bone health

Vitamin D helps build strong bones. It allows both a better absorption of calcium and phosphate in the intestine, but also the reabsorption of calcium in the kidneys. Should we still fear a deficiency when the bone capital is constituted?

“This is not done in one winter, concedes Jean-Claude Souberbielle, but the lack of vitamin D contributes to the loss of bone density after 50. Before this age, we do not have studies to say. And it is very difficult to assess the rate at which bones lose their density because it varies greatly from person to person. »

Vitamin D deficiency is also bad for the muscles

New study shows health risks in case of vitamin D deficiency not only affect the bones, but also the muscles. The study published in April 2021 in the Journal of Endocrinologyreveals that vitamin D deficiency can impair muscle function. Several studies have already established a link between low levels of vitamin D and low muscle strength, particularly in the elderly, but the mechanism involved has never been clearly elucidated.

“Specialized organs within cells, called mitochondria, convert nutrients into energy to meet this demand. Previous studies indicate that a decreased muscle strength in people with vitamin D deficiency may be linked to impaired muscle mitochondrial function,” the researchers explain. They used mice to determine the effects of diet-induced vitamin D deficiency on mitochondrial function of muscles. The mice were fed normal amounts of vitamin D, or no vitamin D to induce deficiency, for 3 months. The results showed that the deficient mice had up to 37% impaired muscle mitochondrial function.

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In other words, vitamin D deficiency impairs mitochondrial function and reduces amount of energy produced in the muscleswhich results in a muscular weakness, the cause of falls in the elderly. Supplementation therefore makes it possible to optimize muscle mass and reduce the risk of fractures

Alzheimer’s, cancers, flu… linked to vitamin D deficiency?

Other pathologies are associated with a lack of vitamin D.

  • In winter, the deficit could be one of the causes of the increase in infectious respiratory diseases. Numerous studies indeed suggest that vitamin D regulates immunity. By activating the anti-microbial response, it would prevent infectious diseases such as colds or flu.
  • “Other studies have shown a higher risk of developing a dementia syndrome, and in particular a Alzheimer’s disease, in the event of a deficiency”, notes Dr Cédric Annweiler, geriatrician. Indeed, vitamin D has anti-inflammatory and antioxidant properties: it protects neurons and vessels, thus influencing cognitive performance.
  • Vitamin D deficiency has also been linked toappearance of cancer (colorectal, breast, pancreas, prostate) and autoimmune diseases (thyroiditis, type 1 diabetes, rheumatoid arthritis, etc.)
  • This deficiency is also associated with an increased risk of hypertension and cardiovascular disease.

But “association” does not mean “causality”. It remains to be confirmed that the lack of vitamin D has a role in the occurrence of all these diseases. It could also be a consequence. And, to date, the studies do not allow to know if the supplementation protects against these diseases.

Vitamin D: what impact on Covid-19?

Since the start of the Covid-19 epidemic, vitamin D has been at the heart of questions. Some studies assure that vitamin D would indeed a protective effect against severe forms of Covid-19, but the data remain insufficient to confirm this with certainty. “Vitamin D cannot be considered a preventive or curative treatment for SARS-CoV-2 infection; but by mitigating the inflammatory storm and its consequences, it could be considered an adjunct to any form of therapy”, specified the National Academy of Medicine in May 2020. During the winter of 2020-2021, several experts also called for supplement the population in vitamin D.

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Since then, new data have emerged. Thus, a study published in June 2021 in PLOS Medicine by scientists from McGill University in Quebec (Canada) suggests that theGenetic evidence does not support vitamin D as a protective measure against the virus. To assess the relationship between vitamin D levels and Covid-19 susceptibility and severity, researchers conducted a randomization study using genetic variants strongly associated with increased vitamin D levels. Results showed only no evidence of an association between genetically predicted vitamin D levels and susceptibility to Covid-19hospitalization or a severe form of the disease.

“Most vitamin D studies are very difficult to interpret because they cannot adjust for known risk factors for severe COVID-19 (e.g., advanced age, institutionalization, chronic disease) that are also predictors of a low vitamin D. Therefore, the best way to answer the question of the effect of vitamin D would be through randomized trials, but these are complex and resource-intensive, and time-consuming during a pandemic,” notes Dr. Butler-Laporte.

Who should take vitamin D supplements?

  • After 65supplementation has an interest in preventing falls and non-vertebral fractures, as for the neck of the femur.
  • “She is also useful in postmenopausal women with osteoporosisbecause the treatments work much less well in the event of insufficiency”, emphasizes Jean-Claude Souberbielle.
  • It is also recommended for overweight, dark-skinned peoplethose who spend little time outside in the summer, who wear covering clothes or who follow a diet, to take supplements, because they often present a deficiency, even a deficiency, especially in winter.
  • Vitamin D supplementation is recommended year-round for pregnant women, breastfeeding women, young children from 2 to 5 years old and elderly people living in institutions.

And for the others?

Jean-Claude Souberbielle is of the opinion to advise the systematic taking, without dosage, of supplements: “If in doubt, it would be a pity not to correct a deficit. Especially since taking vitamin D has not shown any harmful effects. »

Cédric Annweiler, more measured, believes that “it is desirable to systematically supplement populations at very high risk of insufficiency, but it is a priori useless to give it to those who have no insufficiency or deficiencies, since we are not sure of the benefits. »

In video: Should we take vitamin D and calcium to prevent osteoporosis?

A dosage not always useful for the High Health Authority

The High Authority for Health considers that theThe dosage is useful and reimbursed (about 13 euros) only for a few people:

  • children in whom rickets is suspected,
  • adults in whom osteomalacia is suspected,
  • kidney transplant patients,
  • adults who have undergone obesity surgery,
  • and the elderly with repeated falls.
  • A rheumatologist may also prescribe one before instituting treatment for osteoporosis to adjust the dose of medication.

For others, she does not recommend the dosage, which is no longer reimbursed when it is the only way to know your vitamin D status.

“We have to save money, explains Professor Souberbielle. Gold, we do not know the optimal concentration to be achieved to help prevent or slow down the progression of a disease and it is not yet known whether supplementation brings any benefit, apart from musculoskeletal pathologies, of course. In addition, without dosage, we manage to raise the levels of vitamin D in the margin that we want, that is to say between 20 and 60 ng/ml”.

Cédric Annweiler nevertheless considers the dosage useful “because the effects of a blood concentration higher than normal are still little known in the long term”.

If we prefer not to run the risk of lacking vitamin D in winter, three solutions are available to us.

  • Food: Dairy products enriched with vitamin D, such as Calin + yoghurts: “Eating two a day is enough to fill the daily intake”, notes Jean-Claude Souberbielle. Oily fish, egg yolk or mushrooms are rich in vitamin D.
  • Prescription blisters by general practitioners
  • Over-the-counter dietary supplements in pharmacies.

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