Vitamins: role, source, definition

Vitamins are organic substances essential for the proper functioning of the body. Although they are required in very small amounts, they play a major role in many biological processes such as energy production, cell regeneration, and strengthening the immune system. However, only two vitamins can be synthesized by our bodies, making a varied diet essential.

However, certain situations such as pregnancy, food allergies, or specific diets may warrant supplementation. Understanding the roles and sources of vitamins can help you better meet these needs.

What is a vitamin?

A vitamin is an organic molecule essential for carrying out essential biological processes. Unlike macronutrients (carbohydrates, lipids, proteins), vitamins do not provide energy, but they act as catalysts in key biological reactions.

They are divided into two categories:

• Fat-soluble vitamins (A, D, E, K): soluble in fats and stored in the body.
• Water-soluble vitamins (B, C): soluble in water, eliminated daily, and therefore to be consumed regularly.

Vitamins come primarily from food. A balanced diet rich in fruits, vegetables, dairy products, meat, fish, and grains helps meet vitamin needs. However, supplements may be useful in certain situations (pregnancy, deficiencies, specific diets).

The role of vitamins in the body

Vitamins are essential for metabolic balance and the prevention of many pathologies. They are involved in:

• Energy production : B vitamins, such as thiamine (B1) and riboflavin (B2), are directly involved in energy metabolism by helping to convert carbohydrates, lipids and proteins into energy usable by cells.
• Strengthening the immune system : Vitamin C stimulates the production of white blood cells, which are essential for fighting infections. It also acts as an antioxidant, protecting immune cells from damage caused by free radicals.
• Bone health : Vitamin D plays a crucial role in the intestinal absorption of calcium and phosphorus, two minerals essential for bone mineralization and the prevention of diseases such as osteoporosis.
• Cell regeneration : Vitamin A contributes to the maintenance of healthy skin and mucous membranes, as well as to cell growth and differentiation in body tissues.

An imbalance (deficiency or excess) can cause various disorders:

• Deficiencies : Prolonged vitamin C deficiency can lead to scurvy, while vitamin D deficiency can cause rickets in children or osteomalacia in adults.
• Excess : Excessive intake of vitamin A can be toxic and lead to symptoms such as nausea, dizziness, or liver damage.

The different types of vitamins and their functions

Fat-soluble vitamins

Vitamin A

Vitamin A is essential for vision health because it helps form retinal pigments, which are essential for night vision. It also contributes to skin health, wound healing, and the proper functioning of the immune system. Carrots, sweet potatoes, and mangoes are good sources. Vitamin A deficiency can lead to decreased visual acuity in the dark (night blindness) and increased susceptibility to infections.

Vitamin D

Vitamin D plays a central role in the absorption and utilization of calcium and phosphorus, contributing to strong bones and teeth. It is synthesized by the skin under the influence of UV rays, but can also be obtained from oily fish and mushrooms. Vitamin D deficiency can cause bone deformities in children and increased bone fragility in adults.

Vitamin E

As a powerful antioxidant, vitamin E protects cells from oxidative damage caused by free radicals. It plays a role in preventing cardiovascular disease and premature aging. It is found in vegetable oils, almonds, and hazelnuts. Deficiencies are rare but can cause neurological disorders.

Vitamin K

Vitamin K is essential for blood clotting and is involved in bone metabolism to prevent fractures. Leafy green vegetables, such as spinach and kale, are excellent sources. A deficiency can cause excessive bleeding and long-term bone fragility.

Water-soluble vitamins

Vitamin C

Vitamin C is a major antioxidant that strengthens the immune system, improves the absorption of non-heme iron, and promotes wound healing. Citrus fruits, kiwis, and red bell peppers are rich in vitamin C. A deficiency can lead to persistent fatigue, joint pain, and, in severe cases, scurvy.

Vitamin B1 (Thiamine)

This vitamin is crucial for carbohydrate metabolism and energy production. It also plays an important role in nervous system function. It is found in legumes, nuts, and whole grains. A deficiency can cause beriberi, a condition affecting the nerves and heart.

Vitamin B9 (Folic Acid)

Folic acid is essential for red blood cell formation and cell development, especially during pregnancy. Green leafy vegetables, lentils, and chickpeas are excellent sources. A deficiency can cause anemia and fetal developmental abnormalities.

Vitamin B12 (Cobalamin)

Vitamin B12 is essential for red blood cell formation, proper nervous system function, and energy metabolism. It is found primarily in animal products and fortified foods. A deficiency can lead to severe fatigue, anemia, and neurological disorders.

When should you take a vitamin course?

A vitamin treatment can be considered when specific needs of the body cannot be covered by the usual diet or in specific physiopathological contexts.

Compensation for proven deficits:

Diagnosed clinical or biological deficiencies (e.g., vitamin D deficiency in populations living in areas with little sunlight or vitamin B12 deficiency in vegan patients) warrant curative intervention. These deficiencies can impair essential functions, such as bone mineralization or red blood cell production.

Prevention in specific contexts:

Certain populations have increased needs or high risk factors for deficiencies. For example, pregnant women require increased folic acid (B9) intake to prevent neural tube defects in the fetus, and infants are often given vitamin K supplements to prevent hemorrhage.

Support in physiological or pathological conditions:

During periods of high oxidative stress (e.g., recovery from viral illness, surgery), supplementing with antioxidant vitamins like C and E can promote cell regeneration and reduce inflammation. In athletes, increased intake of B vitamins can optimize energy metabolism.

Response to absorption disorders or dietary restrictions:

Pathologies such as chronic inflammatory bowel diseases (Crohn's, ulcerative colitis) or bariatric surgeries can cause micronutrient absorption disorders, justifying specific supplementation to prevent complications (anemia, osteomalacia).

Temporary and adjusted targeting:

Unlike chronic supplementation, a cure is based on a limited duration and an adapted dosage, minimizing the risks of overdose, particularly for fat-soluble vitamins (A, D, E, K). The objective is to correct a transient condition without compromising the overall balance of the body.

In short, a vitamin cure is an approach adapted to individual biological needs. It is not a substitute for a balanced diet, but rather a therapeutic or preventive tool to optimize health in specific conditions.

Precautions and recommendations when taking vitamins

A diet rich in minimally processed foods remains the ideal source of vitamins, but in certain situations, dietary supplements can be a suitable solution. However, it is essential to choose well-dosed supplements, manufactured according to strict standards and registered with competent organizations such as the DGAL (Directorate General for Food) in France. These registrations, in accordance with the recommendations of ANSES or the European Commission, guarantee their safety and the clarity of the information on the label. It is also important to strictly adhere to the indicated doses, as overconsumption, particularly of fat-soluble vitamins (A, D, E, K), can lead to toxic effects. If in doubt or if you have specific needs, it is strongly recommended to consult a healthcare professional for an informed opinion.

Conclusion: A balanced approach to good health

Vitamins play a central role in maintaining vital functions. A varied diet rich in natural products generally covers needs, but specific situations may require supplementation. In synergy with minerals , they help maintain metabolic balance and optimal well-being.

Sources :

• World Health Organization (WHO), “Vitamins and Mineral Requirements in Human Nutrition”.
• ANSES, “Nutritional references for the French population”.
• EFSA, “Scientific Opinions on Dietary Reference Values”.