Introduction:
Vitamin D deficiency is a common health problem worldwide and tends to be a risk factor for all-cause mortality. We evaluated the effect of continuous low-dose oral daily and loading dose of oral weekly and loading monthly intramuscular (IM) vitamin D₃ regimens on circulating levels of total 25(OH)D and in vitamin D deficient females, and between non-obese and obese subgroups.

Material and methods:
A total of 231 vitamin D deficient females were included to the study. According to treatment regimen, patients were divided into three groups: daily continuous oral, loading dose of weekly oral and monthly intramuscular. All patients in treatment groups were divided into non-obese (105) and obese (126) groups. Serum 25(OH)D and parathormone (PTH) levels were evaluated at baseline and at the third and sixth month.

Results:
In obese patients oral weekly loading regimen and in non-obese patients oral daily continuous regimens were found to be more potent. Baseline PTH levels decreased when compared with the third and sixth months (p < 0.001), but between the third and sixth months it was not changed (p = 0.783).

Conclusions:
Oral daily regimen in non-obese patients and loading weekly oral regimen in obese patients were more effective in achieving the target levels of 25(OH)D concentration above 30 ng/ml and provided a stable plasma vitamin D concentration over a long period of time.