Roger-Luc Chayer (Image : Meta AI / Gay Globe)
Vitamin D, as we know, is an essential element for human health thanks to its multiple roles regulating numerous metabolic functions. Long associated with the sun, its production occurs naturally in the body through exposure to sunlight, but it can also be obtained by taking dietary supplements that are widely available on the market. According to the World Health Organization, it is an essential molecule.
What exactly is vitamin D?
Vitamin D is a substance vital for the proper functioning of the human body, primarily recognized for its key role in calcium absorption and bone strength. It is naturally produced by the skin under the influence of ultraviolet rays from the sun, but it can also come from certain foods or nutritional supplements.
Far more than a simple vitamin, it acts as a hormone that influences many biological functions, ranging from immunity to inflammation regulation. A deficiency in vitamin D can lead to weakened bones, impaired immune function, and various more subtle health issues.
Many health specialists now consider that an adequate intake is essential throughout life, especially in regions with limited sunlight exposure. Monitoring vitamin D levels is therefore part of basic recommendations to maintain overall balance and prevent certain diseases.
Since when does a vitamin become a hormone?
Only recently, thanks to scientific and medical research, have we discovered that this simple vitamin is actually a hormone. Two molecules that are theoretically diametrically opposed.
Simply put, a vitamin is an organic substance that the body cannot produce (or not in sufficient amounts) and must obtain from food to function properly. Vitamins often act as cofactors, helping enzymes carry out essential chemical reactions.
A hormone, on the other hand, is a molecule produced by the body itself (endocrine glands, skin, kidneys, etc.) that acts as a chemical messenger. Hormones travel through the bloodstream to send instructions to different organs and tissues, regulating a wide range of functions (growth, metabolism, reproduction, etc.).
Vitamin D is special because, although called a “vitamin,” it acts as a prohormone. Under the effect of sunlight, the skin synthesizes a precursor which is then converted into an active hormonal form (calcitriol). This form notably regulates calcium absorption and plays a broader role in the body, like a classic hormone. Fascinating, isn’t it?
Does it act quickly, or must you be patient?
When vitamin D is taken (through sun exposure, diet, or supplements), it is first absorbed then converted into an active form by the liver and kidneys. This process can take anywhere from a few days to several weeks, depending on the dose, frequency, and the individual’s initial condition.
To correct a deficiency, blood levels often improve within 4 to 6 weeks after starting regular supplementation. Visible effects—on mood, fatigue, immunity, or bone strength—may take longer, sometimes several months, as they depend on the severity of the deficit and each person’s metabolism.
The World Health Organization recommends a daily intake of 1,000 IU (international units). If a deficiency is confirmed by a blood test, a higher dose may be necessary but must be prescribed and monitored by a doctor, as overdose is then possible.
Unlike some water-soluble vitamins (such as vitamin C), which are easily eliminated in urine, vitamin D is fat-soluble: it accumulates in fat stores and can cause toxicity if consumed excessively over a long period. This condition, called vitamin D toxicity, can lead to hypercalcemia (too much calcium in the blood), causing nausea, kidney problems, bone pain, and even heart issues.
In practice, doses above 4,000 IU per day require medical indication. High-dose self-medication is discouraged, as side effects can be serious, though rare.
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