What is Vitamin D and Why is It Important?

Vitamin D is a vital substance required for the proper functioning of the body. It ensures the intestinal absorption of calcium and phosphorus, which are responsible for bone and tooth strength. Additionally, this vitamin plays a crucial role in supporting the immune system and ensuring normal muscle and nervous system function.

The body can obtain vitamin D from three sources:

Synthesis in the skin under the influence of ultraviolet sunlight;
Through food products;
With the help of dietary supplements.

Symptoms of Vitamin D Deficiency

In many cases, the early stages of deficiency may proceed without noticeable symptoms. When levels of this biologically active substance drop significantly, the following signs may occur:

Persistent fatigue and general weakness;
Bone and joint pain (wrists, ankles, shoulders);
Muscle weakness and difficulty walking;
Frequent infectious diseases;
Frequent mood swings, susceptibility to depression, and insomnia;
Hair loss and headaches.

Complications of Prolonged Deficiency

Long-term lack of vitamin D can lead to various serious consequences depending on age:

In children: Rickets may develop, in which bones soften and growth is delayed, resulting in bowed legs, chest, and joint deformities.
In adults: The risk of bone softening (osteomalacia) and bone fragility (osteoporosis) increases, which raises the likelihood of fractures.

Causes of Deficiency and Risk Groups

Vitamin D deficiency is caused by insufficient sunlight, a monotonous diet, and an increased body requirement for this substance. Regular use of sunscreen and reduced solar activity during winter also slow down the synthesis process.

Who is in the risk group?

Older adults (over 65 years old) — with age, the skin's ability to synthesize the vitamin decreases;
Individuals with darker skin tones — pigmentation hinders the deep penetration of sunlight into the skin;
People who spend a lot of time indoors (night-shift workers, homebound individuals);
Individuals who are overweight or have undergone bariatric surgery;
Pregnant and lactating women, as well as infants who do not receive vitamin supplementation.

Diagnosis and Normal Ranges

The most reliable method for determining vitamin D levels in the body is testing the concentration of 25-hydroxyvitamin D (25-OH D) in the blood. Test results are expressed in nanomoles per liter (nmol/L) or nanograms per milliliter (ng/mL):

Severe deficiency: less than 30 nmol/L (12 ng/mL);
Mild deficiency: 30–50 nmol/L (12–20 ng/mL);
Normal range: 50–125 nmol/L (20–50 ng/mL);
High level: greater than 125 nmol/L (50 ng/mL).

In cases of bone pain and serious suspicions, additional diagnostic examinations may be prescribed to evaluate bone mineral density.

Forms of the Vitamin and Absorption

Vitamin D exists mainly in two forms: D2 (ergocalciferol) and D3 (cholecalciferol). Since this vitamin belongs to the fat-soluble group, scientific sources indicate that taking it with fatty food increases absorption efficiency by an average of 32%.

Methods for restoring levels of this biologically active substance, preventive measures, and required dosages are determined individually by a doctor based on specific lab results and the overall health condition of the patient.