The importance of the vitamin in our life and living activity in general is known by everyone. Even in Ancient Egypt people thought that different products and foods had different useful properties for the organism. The scientific researches in this sphere revealed the presence of special substances in the food that is vitally required for the organism of every human being. They were called vitamins from the Latin word "vita" that means "life". Today the vitamins are divided into two main groups: fat-solvent and water-solvent vitamins. Every vitamin is responsible for different functions that it plays in the body. The complex of vitamins in general is required for normal vital activity and physiologic processes in the body.

Vitamin of the D group is considered to be a fat-solvent vitamin. It is collected in the body for some period of time that is why it is very important to avoid overdose.

Vitamin D is required for transporting calcium and phosphorus from the blood to the bone tissue. Vitamin D can be easily received from the sunlight. The ultra-violet rays are absorbed by our skin that converts them into vitamin D and collects it in the fatty layer. Thus, sunbathing is very useful. Vitamin D is also can be received from foods such as fatty fish, fish oils, liver, and milk. Those who have vitamin D deficiency and cannot receive it by means of natural sources are prescribed to take special vitamin D supplements that are available today as liquid vitamin D or in pills.

The categories of people who may suffer vitamin D deficiency and who take vitamin D supplements include those who have the lack of sunlight due to their working conditions, for example, night shift workers or monks. Young children are recommended to take vitamin D supplements as well due to the bones growth to avoid such a disease as rickets. Vitamin D deficiency in old people may also lead to bad absorption of the calcium and phosphorus that causes the general decrease in the bone tissue density and as a result bones fragility appears. Old people should take vitamin D supplements to avoid deficiency and go outdoors more often. The main features of vitamin D deficiency may include shortsightedness, falling of teeth, muscle weakness, hyper-excitability, irritability, insomnia, depression, etc.

Vitamin D supplement review usually helps to reveal the situations when vitamin D is required. Physicians do not recommend using vitamin D supplements if a patient has a high level of calcium in the blood, in the case of allergic reactions and so on. These supplements should be taken with food or drinks in order to avoid disordered stomach. In comparison with other vitamins, the organism is not able to remove the excess vitamin D; the overdose is harmful, though it is noticed extremely rarely. Overdose symptoms may be the following: excessive thirst, vomiting, itch, diarrhea, etc. Those people who are able to go out often in the fresh air should also eat less vitamin D foods than those who usually spend their days inside a closed room.