Vitamin D is a very important nutrient present especially in foods of animal origin such as egg, meat or fish, which when it is in adequate levels, it is essential to prevent the appearance of several types of infectious and chronic diseases, including heart problems, osteoporosis, diabetes and even some types of cancer.  
As vitamin D levels tend to decrease with age, being lower in the elderly, who are the main risk group for the appearance of complications related to COVID-19, it is assumed that vitamin D supplementation or maintenance at optimal levels , with blood tests, may be a way to protect this risk group from the potential complications of coronavirus.
Because of this it is assumed that Vitamin D should be at ideal levels, in any population exposed to coronavirus, through the intake of food sources of this nutrient and also sun exposure for the production of Vitamin D by the body, and even supplementation of Vitamin D when justified in order to prevent infection complications.
How vitamin D protects against viruses
Vitamin D is able to protect against several viruses through 3 different mechanisms: 
- Creation of a physical barrier: the vitamin helps to keep the junctions between cells tighter, creating a barrier that makes it difficult for various types of viruses to enter the body;
- Increased natural immunity of cells: vitamin D increases the action of antimicrobial peptides, which are substances that are present inside cells and eliminate different bacteria, viruses and fungi;
- Decreased inflammation of the body: vitamin D is able to reduce the excessive production of pro-inflammatory cytokines, which are substances that stimulate inflammation in the body and hinder the work of the immune system.
Due to these mechanisms, it is possible that vitamin D, when in ideal doses, is able to protect against the new coronavirus or, at least, reduce its viral load, decreasing the severity of the infection and preventing the appearance of serious complications, such as pneumonia.
In addition, vitamin D levels tend to decrease with age, being lower in the elderly, who are the main risk group for the appearance of complications related to COVID-19.
What are the ideal levels of vitamin D
There is still no consensus among the various Societies on what the ideal level of vitamin D should be, however, according to the Brazilian Society of Endocrinology and Metabology and the authors of the review done in the United States  the concentration of vitamin D, in adults, it should be above 30 ng / mL.
To check vitamin D levels in the body, a specific blood test must be performed, which evaluates the amount of this vitamin in the blood, and must be ordered by the doctor. Learn more about the vitamin D exam .
How to increase vitamin D levels
One of the main sources of vitamin D is the production that takes place in the skin, which is greater when there is exposure to UVB rays. However, this type of vitamin can also be consumed in the diet or through supplementation.
The most used ways to increase vitamin D levels are:
- Soak up the sun for 15 to 30 minutes, without sunscreen, at a time of lower heat, ie before 10am or after 3pm. See how to sunbathe to produce more vitamin D ;
- Increase consumption of vitamin D-rich foods, such as cooked salmon, oysters, boiled eggs or sardines. Check out a list of the main foods rich in vitamin D ;
- Take vitamin D supplements.
However, supplementation should only be done under the guidance of a doctor, as the doses and duration of treatment vary according to age and the degree of vitamin deficiency in the blood. Excessive consumption of vitamin D can cause hypervitaminosis.