Except in special cases, a balanced diet provides all the necessary vitamins to get through the bad days.
A cachet of vitamin C to "boost" its immune defenses, a vitamin D ampoule to strengthen its bones, a vitamin B capsule to replenish energy. With the arrival of the bad days, it is the big return of the cocktails of food supplements, often perceived as unavoidable allies of the winter. This is evidenced by the French turnover of this booming market, estimated at 1.8 billion euros last year, nearly 6% more than in 2016, according to Synadiet.
However, vitamins found in commerce have no preventive or curative action. These products, which are dietary supplements (and not drugs), do not have the right to post such claims or to believe that the diet does not provide enough vitamins.
What are vitamins for?
The word "vitamin" is surrounded by an aura almost mystical: nobody really knows what it looks like but everyone is convinced that it is a miraculous fuel. And it's true, vitamins (13 in total) are essential to the functioning of the body. On paper, however, the reality is less epic. Biologically, each vitamin acts as a carrier for well-defined chemical reactions within cells. The body does not know how to make them (or it manufactures them in insufficient quantities), so they come almost exclusively from our diet and they participate in multiple tasks ranging from the stimulation of the immune system to the bone mineralization, through training red blood cells.
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Does vitamin supplementation help improve health? In case of deficiencies, that's for sure. For example, a significant and prolonged vitamin C deficiency leads to scurvy. But unless you never eat fruits and vegetables, this type of deficiency is extremely rare. Sometimes there is a slight deficiency in this or that vitamin, but it is usually transient and has no impact on health. On the other hand, certain diseases such as Crohn's disease require preventive supplementation with certain minerals and vitamins. In a healthy person, a balanced and diversified diet is usually enough to cover all needs.
Be careful, this is not to say that vitamin supplementation is always useless. In some cases, it is even essential. Women who wish to have a child or pregnant systematically receive vitamin B9 to reduce the risk of neurological malformations in the fetus. Another example: all infants receive vitamin K to prevent the risk of bleeding disease. Finally, it is recommended that people who follow a vegan diet supplement vitamin B12, because it is found exclusively in foods of animal origin.
Vitamin C, little or no effective against colds
It's a tough idea: Vitamin C would help the body fight colds. It was popularized in the 1970s by Linus Pauling, an American chemist awarded the Novel Chemistry Prize in 1954. Since then, several scientific teams have been studying the question. In 2013, a large study showed that taking vitamin C does not help to prevent getting sick. Results confirmed by another study published in August. This month, another large-scale study concluded that "vitamin C has minimal or no impact on the duration of colds".
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Vitamin D, no consensus
Should I take vitamin D in winter? It plays an important role in bone mineralization (among others), and has the particularity of being synthesized in the skin under the effect of UV emitted by the sun. For fair-skinned people, exposing their arms for five minutes each day in the sun can produce the vitamin D needed by the body. For people with dark skin, you have to expose yourself a little longer. But during the winter in the countries of the northern hemisphere, the reduced sunshine pushes many doctors to advise to supplement themselves. However, work tends to put into question, on the one hand the thresholds below which one speaks about deficiency, on the other hand the utility of the supplementation in a certain number of pathologies.
To know his vitamin D level, it is possible to make a blood test (not reimbursed except special diseases) and, in case of deficiency, to be prescribed by a doctor. Vitamin D supplements are also available over the counter, and are found in oily fish such as salmon, herring and sardines.
Be careful, even if they are "natural" products (but in practice synthesized in the laboratory), vitamins in the form of food supplements are not without risks. For example, an excess of vitamin C can interfere with the body's ability to absorb certain minerals, which can cause other imbalances.