Introduction and objective:
Lichen planus is a chronic inflammatory skin disease involving the mucous membrane of the oral cavity. It is postulated that different factors play a role in the occurrence of the disease and may activate the immune system, thus influencing the development of lichen planus. Vitamin D is a steroid prohormone with multiple systemic effects.

Objective:
The aim of this study was to assess oral lichen planus against 25-hydroxy-vitamin D3 serum level. Vitamin D takes an active part in the pathogenesis of immunisation diseases, may have also a beneficial effect on oral health.

Material and methods:
The clinical picture of lichen planus was analyzed according to the concentration of 25-hydroxy-vitamin D3. Patients were given a questionnaire interview which included questions about the co-existence of systemic diseases, subjective complaints, and information relating to the individual course of the disease. In the next stage of the study, patients were underwent a physical examination. Laboratory determinations of the concentration of 25-hydroxy-vitamin D3 were also performed.

Results:
The mean vitamin D concentration in patients with lichen planus in the oral cavity was 14.37 ± 4.95 ng/ml. An insufficient level (10–30 ng/ml) was detected in 84.91% of the examined patients, whereas a deficiency (< 10 ng/ml) was observed in 15.09% of those patients. None of the analyzed patients had vitamin D level in the range of established clinical standards. A substantially lowered vitamin D level was found in patients reporting bleeding and pain of the gums.

Conclusions:
The study enhances relationship between reduced levels of vitamin D3 and lichen planus in patients with oral lesions. Thus, vitamin D3 control and supplementation may play an important role in the treatment of lichen planus.