What is it?
Vitamin D, also called calciferol, is a prohormone that primarily contributes to bone growth. Its origin is twofold: it is both synthesized by the body and obtained through the diet.
The synthesis of vitamin D is stimulated by exposing our skin to ultraviolet sunlight, particularly UVB. Minimal sun exposure is therefore necessary for the body to produce it.
Vitamin D affects several functions of the body:
- Elle intervient sur l’absorption du calcium et du phosphore, au niveau des intestins. Elle assure la minéralisation des os, des articulations influant ainsi sur la croissance osseuse. Identifiée en 1922 par Elmer McCollum dans le cadre des soins apportés contre le rachitisme (maladie entraînant des retards de croissance osseuse du fait d’un déficit en vitamine D), elle a permis de lutter efficacement contre cette maladie.
- Elle limite les fractures osseuses, en assurant la solidité des os et des dents.
- Elle limite l’apparition de l’ostéoporose chez les personnes âgées. Cette maladie entraîne une diminution de la densité osseuse, ce qui fragilise les os du corps.
- Elle renforce la tonicité des muscles en favorisant le renouvellement des fibres musculaires et la contraction musculaire, lors des mouvements.
- Elle assure une fonction protectrice des cellules neuronales et retarde le déclin cognitif.
- Elle assurerait également des effets protecteurs contre les maladies cardio-vasculaires, le diabète et certains cancers. Toutefois, ces dernières fonctions n’ont pas été formellement prouvées.
The benefits of vitamin D
The benefits of vitamin D stem from its role in the body. Essential for ensuring the growth and health of the bones, vitamin D helps regulate blood calcium levels and the absorption of phosphorus. If the body were to lack vitamin D, calcium would be eliminated in the urine by the kidneys.
It therefore allows calcium to be absorbed and to be “fixed” onto the bones, ensuring their development.
A vitamin D deficiency can lead to rickets in children (growth retardation) and osteomalacia (reduced bone density), osteoporosis (weakened bones due to decreased density), or hypocalcemia (abnormally low blood calcium levels) in adults.
It is therefore essential not to neglect dietary sources of vitamin D and to regularly check the blood level of this vitamin in the body.
Studies are currently underway to demonstrate the beneficial effects of vitamin D on reducing the progression of certain cancers (notably colon cancer), limiting the onset of multiple sclerosis and Alzheimer’s disease, as well as reducing several cardiovascular diseases and seasonal depression.
Read also | Our tips for choosing the best vitamin D
Note: about 15 to 30 minutes of sun exposure, twice a week, is sufficient to ensure adequate vitamin D intake in an adult. Don’t hesitate to expose yourself to the sun when you have the opportunity to promote vitamin D synthesis. Don’t forget to protect your skin by applying an appropriate sunscreen.
Deficiency symptoms
To benefit from vitamin D supplementation, it is helpful to highlight the symptoms that may warn of a possible deficiency. You should act when the following symptoms are observed:
- Douleurs musculaires, douleurs osseuses
- Douleurs articulaires
- Douleurs dorsales
- Fatigue chronique
- Déprime passagère
- Être souvent malade ou contracter des infections plus souvent
- Altération de la cicatrisation
- Chutes fréquentes (surtout chez les personnes âgées)
To confirm a deficiency, a blood test can be performed by taking a simple blood sample. This laboratory test makes it possible to check the vitamin D level in the blood and thus determine the body’s needs.
Recommended nutritional intakes
Essential at all stages of life, vitamin D requirements nevertheless vary according to an individual’s stages of growth. Infants, young children and adolescents are in a growth process, so their vitamin needs will be higher, for example.
Nutritional reference values or recommended intakes for vitamin D are expressed in micrograms (µg) or international units (IU). They correspond to:
- Nouveau-nés/bébés jusqu’à 12 mois : 20/25µg ou 800/1 000 UI par jour
- Enfants âgés de 1 à 3 ans : 10 µg/jour, soit 400 UI/jour
- Enfants âgés de + de 36 mois, adolescents de 12 à 18 ans et adultes : 15 µg/jour, soit 200 UI/jour
- Enfants âgés de 1 à 3 ans : 10 µg/jour, soit 400 UI/jour
- Enfants âgés de + de 36 mois, adolescents de 12 à 18 ans et adultes : 15 µg/jour, soit 200 UI/jour
- Au-delà de 75 ans : 10 à 15 µg/jour, soit 400/600 UI/jour
Pregnant women or those who are breastfeeding should be attentive to their vitamin D intake. Indeed, some scientists believe that vitamin D may help prevent pre-eclampsia and gestational diabetes.
The recommended vitamin D intake for pregnant women is 10 µg/day, or 400 IU/day. Note: to prevent vitamin D deficiency in young children in France, children aged 0 to 18 months receive vitamin supplementation. This measure helps limit the occurrence of rickets and promotes healthy growth in children.
Top 5 foods that contain vitamin D
A few reminders: vitamin D is both synthesized by the body (from the epidermis) and supplied by the diet. It exists in two distinct forms: vitamin D2, found in certain plant sources, or vitamin D3, found in animal sources. Vitamin D2 is also called ergocalciferol, while vitamin D3 is called cholecalciferol.
Vitamin D is present in few foods. However, it is possible to add vitamin D-rich products to your diet. Especially during the winter months, when sunny days are less frequent and our exposure is reduced.
1. Cod liver oil
Cod liver oil brings back bad memories for our elders. Their grandmothers used to give a teaspoon of cod liver oil to their children to ensure their good health. And they weren’t necessarily wrong!
Cod liver oil is very rich in vitamin D. It contains 250 µg per 100 g. A teaspoon provides 37.5 µg of vitamin D, or three times the recommended daily intake! So it’s worth adding it to the menu to avoid deficiencies. Cod liver contains 100 µg of vitamin D per 100 g.
2. Fatty fish
Fatty fish have many benefits and are definitely excellent for your health. They contain omega-3s, good for the brain, sleep or for reducing stress, but also vitamin D.
Don’t hesitate to add sardines, tuna, mackerel, or salmon to your meals to reap their benefits.
To avoid preparing dishes that are too high in fat, it is preferable to eat this type of fish grilled, baked, or cooked in foil, accompanied by vegetables and starchy foods.
3. Eggs
Eggs, rich in protein, are beneficial for the brain. They also contain vitamin D (0.94 µg/egg).
Eggs are ideal for evening meals. Eat them hard-boiled, in a salad, or as an omelet, accompanied by soup, green vegetables, or a green salad.
4. Milk and dairy products
Milk, butter, yogurts, and fromage blanc contain vitamin D. Some dairy products are even fortified with vitamin D and marketed for their benefits on growth and bone strength. It’s a marketing argument, certainly, but a proven one.
Enjoyed at breakfast, lunch, or dinner as a dessert or snack (a glass of warm milk before bedtime), dairy products easily complement your daily meals.
5. Mushrooms
Mushrooms, notably chanterelles, morels, or shiitake mushrooms (Japanese mushrooms), are also a source of vitamin D. The advantage of these foods is that they are low in calories. You can consume them in large quantities.
Cooking mushrooms in a pan, in a vegetable oil rich in omega-3s, allows you to make delicious side dishes for your meats and fish. You can eat them with a serving of starchy foods to create nourishing and healthy meals.
Dangers and adverse effects, vitamin D overdose
We now know the effects of vitamin D deficiency. What happens when vitamin D intake is too high? What are the risks of overdose?
The vitamin D overdoses have become rare because intake is better controlled.
However, overdoses can cause hypercalcemia (blood calcium levels that are too high), leading to hypercalciuria (urine calcium levels that are too high). Excessive blood calcium concentration can lead to the formation of kidney stones (“small stones” present in the kidney).
These stones can cause significant pain and lead to complications such as renal colic. The deposition of calcium in the kidneys is called nephrocalcinosis, a kidney disease that can also result from a vitamin D overdose.
Hypercalcemia occurs when an individual is exposed to doses higher than 40,000 IU/day. The symptoms of vitamin D overdose are the following:
- Etat nauséeux ou vomissements
- Asthénie (fatigue)/somnolence
- Céphalées (maux de tête)
- Déshydratation/grande soif
- Faiblesse et douleurs musculaires
- Anorexie
- Augmentation du taux d’azote sanguin (azotémie)
To avoid deficiencies or overdoses, it is important to assess blood vitamin D levels by performing regular blood tests. These tests are performed by medical prescription.
