Background and purpose: Vitamin D is a steroid hormone. It plays an important role in bone metabolism and neuromuscular function. It is mainly synthesis from converting 7-dehydrocholesterol to cholecalciferol on skin with exposure to sunlight. This study aimed at comparing the serum levels of 25-hydroxyvitamin D after taking parenteral and oral vitamin D in patients with vitamin D insufficiency.

Materials and methods: This historical cohort study was done in 400 patients with vitamin D insufficiency attending Rheumatology and Endocrinology clinics in Sari, 2013-2014. The patients were treated either by vitamin D3 (cholecalciferol) orally (control group) or injection (case group).

Results: The patients were 333 females (83%) and 67 males (16.8%). Two hundred forty four patients received intramuscular (IM) and 158 received oral vitamin D3. The mean serum levels of 25 (OH) D before and after the intervention in oral group were 17.16 ± 0.39 and 43.02 ± 0.48 ng/ml, respectively (P <0.010) and in IM group were 17.71± 0.32 and 41.72± 1.20 ng/ml, respectively
(P< 0.001). The mean serum levels of 25 (OH) D before and after the intervention were not significantly different between the two groups (P= 0.48).

Conclusion: Administration of oral or injectable vitamin D led to increase in 25 (OH) D levels, but there were no difference in terms of the effects or compilations. According to the requirements and wishes of the patients either the oral or injectable form could be administered for prevention or treatment.