Background and aims Vitamin D deficiency has been associated with growth failure and rickets during childhood period. Turkish Ministery of Health recommends 400 IU of vitamin D supplementation during the first year of life in order to prevent rickets and vitamin D deficiency. Vitamin D has been started to be supplemented free of charge to all infants under 1 year of age since 2005. The aim of our study was to determine the serum 25-(OH) vitamin D (25-OHD) levels, the prevalence of vitamin D deficiency and insufficiency and the factors that influence the vitamin D status among healthy children aged 3–36 months.

Methods The study group consisted of healthy children who admitted to the outpatient Healthy Child Clinics of Istanbul University, Cerrahpasa Medical Faculty for their routine control and vaccination between 1.9.2013 and 31.11.2013. A questionaire regarding the duration of vitamin D prophylaxis, dose, duration of sun exposure, duration of breastfeeding, consumption of Vitamin d-rich foods, maternal vitamin D prophylaxis during pregnancy and lactation, the educational status and clothing style of the mother, was given to the parents of each child. The levels of 25-OHD, paratyhroid hormone (PTH), calcium (Ca), phosphorus (P) and alkaline phosphatase (ALP) were determined in every child.

Results A total of 190 healthy children (102/88: male/female) with a mean age of 15.9±10.4 months were enrolled. The mean 25-OHD level was 38.1±16.2 ng/ml. 25-OHD level was<30 ng/ml in 33.2% of children of which 13.6% were in the deficiency range (<20 ng/ml) and 19.5% were in the insufficiency range (20–29 ng/ml). Of the enrolled children who were≤1 year of age, 89.2% were on vitamin D prophylaxis while 20.2% of those>1 year of age were on prophylaxis. The percentage of children with 25-OHD levels in the sufficiency range was significantly higher in children receiving vitamin D than those not receiving it (p=0.04). 25-OHD levels were in the sufficiency range (≥30 ng/ml) in 64.9%, 81.4% and 100% of children who received vitamin D at a dose of 400 IU, 400–800 IU and>800 IU, respectively. The PTH and ALP levels were found to be higher in children with 25-OHD levels<30 ng/ml than those with levels≥30 ng/ml. The only variables that had an effect on the vitamin D status were to receive vitamin D prophylaxis and the dose of vitamin D for prophylaxis.

Conclusions Vitamin D deficiency and insufficieny remain a serious public health concern worldwide. Not only the deficiency but also the insufficiency of vitamin D can be associated with many health related issues given the proposed role of vitamin D in many systems as vitamin D receptor (VDR) is expressed in various organs and tissues of the human body other than bone cells such as the kidney, the colonic mucosa and immune cells. Our study showed that vitamin D prophylaxis and dose of vitamin D had an influence on vitamin D status of the child. However, further studies are needed to determine the optimal dose and duration of vitamin D prophylaxis among healthy children.