Effects of vitamin D-fortified oil intake versus vitamin D supplementation on vitamin D status and bone turnover factors: A double blind randomized clinical trial

Purpose: The aim of this study was to compare the effect of vitamin D fortified oil consumption and vitamin D supplementation on serum 25-hydroxy vitamin D and bone turnover factors.

Methods: This study was a double-blind, parallel, randomized controlled clinical trial conducted over 12 weeks on 93 healthy participants aged 18-30 years. Participants were randomly allocated to 1 of the 3 groups: (a) supplement (a tablet of 1000 IU vitamin D supplement + 25 g canola oil daily, n = 31); (b) fortified oil (a placebo tablet + 25 g canola oil fortified with 1000 IU vitamin D daily, n = 30) and (c) control (a placebo tablet + 25 g canola oil, n = 32). Before and after the intervention 25-hydroxy vitamin D (25(OH)D¹), parathyroid hormone (PTH²), bone alkaline phosphatase (BAP³) and collagen type 1 cross-linked C-telopeptide I (CTX⁴) were assessed.

Results: Serum 25(OH)D increased more in the vitamin D supplement group compared to the controls (P = 0.001). In addition, subgroup analysis revealed that just in the vitamin D sufficient subgroup, serum 25(OH)D increased more in both vitamin D supplement group and vitamin D fortified oil group, compared to the controls (P = 0.001 for both). The mean differences of PTH, BAP, and CTX were not significantly different among the study groups.

Conclusion: Consumption of 1000 IU vitamin D per day for 12 weeks as a supplement or fortified oil could enhance the serum vitamin D in main population. However, the protective effect of vitamin D supplementation and oil fortification was seen just in vitamin D sufficient subgroup, not vitamin D deficient one. Besides, this dose of vitamin did not have a noticeable effect on bone turnover markers in this period. Registered under Iranian Registry of Clinical Trials (IRCT.ir) with ID number of: IRCT20180708040401N1.