Prevalence of vitamin D deficiency in children in the northern country during winter season is very high (up to 90%). Vitamin D supplementation at a dose 600 -1000 IU/d is recommended in Polish children from September till April. However, there is shortage of studies in Polish children. The aim of the study is to assess the effectiveness of vitamin D supplementation in the prevention of vitamin D deficiency in Polish children (4-10 years of age).

Prevalence of vitamin D deficiency in children in the northern country during winter season is very high (up to 90%). Vitamin D supplementation at a dose 600 -1000 IU/d is recommended in Polish children from September till April. However, there is shortage of studies in Polish children.

Aims:

1. Assessment of the impact of vitamin D intake at a dose of 1000 IU / day on vitamin D status in children aged 4-10 years.
2. Evaluation of the effectiveness of supply of vitamin D at a dose of 1000 IU / day in preventing vitamin D deficiency and maintaining optimal vitamin D status ( 25OHD level >30ng/ml)
3. Evaluation of vitamin D status depending on age, BMI and body composition.
4. Assessing the safety and tolerability of mel ● tiki vitamin D in children. Material: Children aged 4-10 years Study desing: Prospective intervention trial Intervention: cholecalciferol at a dose 1000 IU/day for 3 months

Methods:

1. Analysis of clinical characteristics (attendance at kindergarten / school, consumption of products rich in vitamin D, exposure to sun, use of sunblock's, the overall child's health (chronic diseases, medications, vitamins, micronutrients)
2. Anthropometric measurements (body weight, height, BMI, assessment of body fat content - body composition by bioimpedance method- TANITA)
3. Assessment of vitamin D status (serum total 25OHD concentration in blood serum by immunochemiluminescence method)
4. Collecting data on the tolerability and safety of meliki ● tiki vitamin D including possible symptoms of vitamin D overdose

Inclusion Criteria:

• Age 4-10 years; declaration of no use other preparations containing vitamin D; parental written informed consent

Exclusion Criteria:

• Osteoporosis, autoimmunological disorders, sarcoidosis, exacerbation of asthma, hypercalcemia, nephrolithiasis, renal insufficiency, nephrotic syndrome, cholestasis, hepatitis, diabetes typ 1, anticonvulsant treatment, prolonged treatment with steroids, cimetidine, ketoconazole, teophiline, diuretics, anti-tuberculosis drugs, participation in another clinical trial