Why are we sick in winter?

Many people will blame the cold.

The body does tend to be weakened by low winter temperatures as it struggles to keep warm.

There is another unknown cause that involves the weakening of the immune system in winter. During this period days are shorter and the sun is weaker than in spring or summer thus leading to a deficiency in vitamin D.

Vitamin D is active in numerous physiological processes and plays an important part in the immune system. 90% of vitamin D is produced through the skin by photosynthesis during exposure to the sun. Under the influence of ultraviolet rays cholesterol produces vitamin D3 that is important for the liver and the kidneys.

Food provides a little vitamin D (fish, seafood, eggs and butter) but to receive the recommended daily dose one would have to eat 20 eggs or 5 packets of butter !!! It is therefore essential to be exposed to the sun to absorb vitamin D.

But what is the connection with the immune system ?

Lymphocytes T and B, macrophages and cells presenting antigen show a receiver with vitamin D (VDR). When the body is deficient in vitamin D its functions are disturbed

     - when a pathogenic element penetrates it is recognized by both lymphocytes T and B and if vitaminin D in the blood is too low T and B will not be differentiated

    - a high rate of vitamin D allows the macrophages to produce anti-infection peptides called cathelicidine. These peptides act in the intestine, the lungs and on the skin as natural antibiotics. They destroy the infection

   - finally, vitamin D regulates the production of cytokine produced during an inflammatory reaction called TNF. Insufficient vitamin D during an infection increases TNF in the body which acts on macrophages and stimulates the process of phogocytose, the production of oxidizers and pro-inflammatory lipids. The infection is therefore made worse !

To fight this indesirable effect there are several solutions :

  - Luminotherapy (or light therapy) is an alternative medicine which consists of exposing the eyes to artificial light similar in intensity to sunlight. This compensates for the lack of sunlight during the winter and stimulates the production of vitamin D.

  - To increase the amount of vitamin D in our diet we need cod-liver oil, full-fat milk, fish etc…

It is also a good excuse to go somewhere sunny in the winter !