Vitamin D

Vitamin D

Vitamin D, or calciferol, is a fat-soluble vitamin that performs many functions in the body.

It is best known for its benefits to bone health and the immune system.

Vitamin D synthesis is directly linked to exposure to sunlight, which is why certain times of the year with little sunlight are prone to vitamin D deficiency.

Vitamin D characteristics

  • A fat-soluble vitamin synthesised from the sun's UVB rays.
  • It exists in two forms, D2 and D3.
  • Found mainly in fish and dairy products
  • Preserves bone and muscle tissue
  • Deficiency may be a risk factor for osteoporosis

Why eat foods rich in vitamin D?

Healthy bones and teeth

Vitamin D promotes intestinal absorption of phosphorus and calcium.

This vitamin is actively involved in the mineralisation and strengthening of bone tissue and teeth.

Vitamin D therefore plays an important role in the prevention and treatment of osteoporosis.

Strengthens the immune system

Calciferol can play an important role in the prevention of certain autoimmune diseases, such as type 1 diabetes or rheumatoid arthritis.

Its protective effect against breast and colon cancer, type 2 diabetes and certain cardiovascular diseases is still being investigated.

Maintains brain and muscle function

Vitamin D is essential for the contraction and regeneration of muscle tissue, as it is involved in the absorption of calcium and phosphorus.

It can help slow the loss of muscle mass, especially in older people.

It also protects the brain from premature decline in cognitive function.

Where can we find vitamin D?

Vitamin D is mainly found in fish and dairy products, especially when fortified.

Contrary to popular belief, there are no vegetables or fruits that are particularly rich in vitamin D.

If you are on a vegetarian or vegan diet, supplementation may be useful.

In food

  • Cod liver oil (1 tablespoon of cod liver provides 1,360 IU of vitamin D)
  • Oily fish
  • Chicken liver
  • Margarine
  • Egg yolk
  • Full and semi-skimmed dairy products
  • Cereals

Sunlight (UVB rays)

Vitamin D can be synthesised in the skin by the action of the sun's UVB rays.

It is the main source of vitamin D in many countries.

For most people, vitamin D synthesis from sunlight accounts for about 80-100% of their vitamin D intake.

Food supplements

Vitamin D can be found in food supplements (capsules, drops).

Daily requirement of vitamin D

Recommended dietary intake

  • Infants 0-6 months = 20-25 mcg
  • Infants 7-12 months = 10mcg
  • Infants 1-3 years = 10mcg
  • Children 4 to 8 years = 15mcg
  • Boys 9 to 13 years = 15mcg
  • Girls 9 to 13 years = 15mcg
  • Boys 14 to 18 years = 15mcg
  • Girls from 14 to 18 years = 15mcg
  • Men from 19 to 50 years = 15mcg
  • Women aged 19 to 50 = 15mcg
  • Men aged 50 and over = 15µg and 20µg if aged 70 and over
  • Women aged 50 and over = 15 µg and 20 µg if aged 70 and over
  • Pregnant women = 10mcg
  • Nursing women = 10mcg

Vitamin D supplements: dosage and indications

Vitamin D-based supplements are particularly good for promoting bone and muscle health.

They also stimulate the immune system and maintain cognitive function.

You can find supplements in oily or capsule form, based on vitamin D2 or vitamin D3.

It seems that the oily form of vitamin D3 is better absorbed by the body.

The dosage of vitamin D is usually 15 to 30 micrograms per day.

If you have any questions about this, ask your doctor for advice.

Vitamin D deficiency

Vitamin D deficiency can lead to bone mineralisation defects and rickets in young children.

In adults, calciferol deficiency results in bone demineralisation and loss of muscle mass, which can lead to osteoporosis.

If skeletal demineralisation becomes significant, convulsions or tetany may occur.

Lastly, in the long term, vitamin C deficiency can lead to a decline in cognitive function and an increased risk of certain diseases (cancer, heart disease, etc.).

Consequences of excess vitamin D

At very high doses, vitamin D causes excess calcium in the blood (hypercalcaemia) and urine (hypercalciuria) and promotes the formation of calcium oxalate-based kidney stones.

In healthy adults, the authorities recommend that vitamin D intake should not exceed 115 micrograms per day.

Contraindications

It is not recommended that you take vitamin D supplements if you have kidney stones.

Certain molecules used to treat epilepsy, AIDS and obesity can reduce the absorption of vitamin D.

Vitamin D Chemical properties

Vitamin D is a fat-soluble vitamin that can be obtained from food or synthesised in the human body under the action of UVB rays during exposure to the sun.

Vitamin D is fat-soluble and its absorption is facilitated by the presence of fats.

There are two types of vitamin D in the diet:

  • Vitamin D2, or ergocalciferol, comes from foods of plant origin;
  • Vitamin D3, or cholecalciferol, comes from animal foods or is synthesised by humans after exposure to the sun.

Once ingested or synthesised by UV rays, vitamin D is transported to the liver, where it is hydroxylated to form calcidiol.

In the kidney, calcidiol is converted to calcitriol, the active form of vitamin D.


Vitamin D