Vitamin D Deficiency

General text about the lack of vitamins can be found here.


The term vitamin D describes a whole group of fat-soluble substances. Particularly important are vitamin D2 (ergocalciferol) and D3 (cholecalciferol). Both subtypes are digested, vitamin D2 is present in plants (e.g. fungi) and vitamin D3 is of animal origin (fish oil, eggs and meat). Our body is not fully dependable on digested vitamin D as it can produce vitamin D3 from cholesterol. However, this production takes place in the skin and it requires sunlight, more precisely its UV component.


In the liver, both vitamins D2 and D3 are converted to a compound known as calcidiol and it is then converted in the kidneys to the final substance calcitriol. Calcitriol is the active form of vitamin D.


Summarize: Vitamin D is taken in food, but we can produce it as well with adequate sun exposure. On the other hand, the formation of the active form of vitamin D is a complex process that requires properly functioning liver and kidneys.


Vitamin D deficiency is usually due to insufficient intake of vitamin dietary combined with the lack of sun exposure. It is a common problem of people in North America and Northern Europe and paradoxically also of Muslim women in Africa and Arabian Peninsula (because of religion-related covering of their bodies in public places). Another problem may be diseases related to malabsorption of nutrients in digestive tract that may also affect vitamin D absorption. Liver diseases (e.g. liver cirrhosis) and kidney diseases (chronic kidney failure) may affect conversion of D2 and D3 vitamin to the active form. Vitamin D deficiency is frequently found in patients in critical conditions and in chronically dialysed patients.


Vitamin D has complex effects, especially on bone metabolism. It helps absorb calcium in the intestine and promotes bone mineralization. The deficiency leads to decreased mineralization of bones, which causes rickets in children and softening of bones and osteoporosis in adults. Many people complain about bone pain, typically of the lower extremities. It is assumed that there is a tight relationship between vitamin D and the immune system and therefore, the lack of vitamin D may lead to weakened immunity with recurring infections. 


We should anticipate the vitamin D deficiency in patients with mentioned risk factors (see Causes). Laboratory examination allows us to measure the level of calcidiol, which allows us to determine the amount of vitamin D in the body.


People with low level of vitamin D should be supplemented. The drug has oral form (usually oral droplets) and should be taken regularly. It is necessary to adhere to the dosage prescribed by the doctor as excessive intake of vitamin D may cause an overdose with increase of serum calcium and other complications including constipation, loss of appetite and formation of calcium deposits in the heart and kidneys, causing their damage.


Jiri Stefanek, MD  Author of texts: Jiri Stefanek, MD
 Sources: basic text sources