Background: Many residents of the United States and Canada depend on dietary sources of vitamin D to help maintain vitamin D status. Because few natural food sources contain vitamin D, fortified foods may be required.
Objective: We aimed to determine the effects of vitamin D-fortified foods on serum 25-hydroxyvitamin D [25(OH)D] concentrations.
Design: We searched MEDLINE (1966 to June Week 3 2006), Embase, CINAHL, AMED, Biological Abstracts, and the Cochrane Central Register of Controlled Trials for randomized controlled trials (RCTs) comparing vitamin D-fortified foods with a control and reporting serum 25(OH)D concentrations. Two reviewers independently determined study eligibility, assessed trial quality, and extracted relevant data. Disagreements were resolved by consensus. Meta-analyses of absolute mean change in 25(OH)D were conducted by using a random-effects model, with evaluation of heterogeneity.
Results: Nine RCTs (n = 889 subjects) were included, of which 8 consistently showed a significant beneficial effect of food fortification on 25(OH)D concentrations. Although 7 RCTs (n = 585 subjects) potentially were meta-analyzable, we were unable to combine the overall results because of significant heterogeneity. The individual treatment effects ranged from 14.5 (95% CIs: 10.6, 18.4) nmol/L to 34.5 (17.64, 51.36) nmol/L (3.4-25 microg vitamin D/d). Subgroup analyses showed a reduction in heterogeneity and significant treatment effect when 4 trials that used milk as the fortified food source were combined.
Conclusion: Most trials were small in size and inadequately reported allocation concealment, but results showed that vitamin D-fortified foods improved vitamin D status in adults.