A randomized, controlled trial evaluating the efficacy of an online intervention targeting vitamin D intake, knowledge and status among young adults

Background: Vitamin D plays a key role in bone health. Consuming adequate vitamin D during young adulthood is important due to the development of peak bone mass; however, many Canadian young adults do not meet vitamin D recommendations. This study aimed to improve knowledge, perceptions, dietary intake and blood concentrations of vitamin D among a sample of young adults.

Methods: Using a pre-post design, 90 Ontario adults (38 men, 52 women; 18-25 years), were randomly assigned to intervention or control groups. Participants completed a socio-demographic survey, pre-post food frequency questionnaire, and a vitamin D knowledge questionnaire (3 time-points). The intervention group watched a video, received online information and tracked intake of vitamin D using a mobile application for 12 weeks. A sub-sample of participants completed pre-post blood 25(OH)D₃ tests. Univariate ANOVA tested pre-post between-group differences in vitamin D intake and status. Repeated-measures ANOVA tested between-group differences in vitamin D knowledge and perceptions across 3 time-points.

Results: Mean vitamin D intake in the sample increased significantly from pre-test (M = 407, SD = 460 IU) to post-test (M = 619, SD = 655 IU), t(88) = 5.37, p < 0.001. Mean intake increased significantly more in the intervention than control group after controlling for gender and education, F(1, 85) = 4.09, p = 0.046. Mean blood vitamin D₃ was significantly higher among non-Caucasian than Caucasian participants at baseline, t(56.7) = 3.49, p = 0.001. Mean blood vitamin D₃ increased significantly from pre-test (M = 28, SD = 16 nmol/L) to post-test (M = 43, SD = 29 nmol/L), t(53) = 11.36, p < 0.001, but did not differ significantly between groups. The increase in vitamin D knowledge from time 1-3 was significantly higher in the intervention than control group (t(88) = 2.26, p = 0.03). The intervention group (M = 3.52, SE = 0.13) had higher overall perceived importance of vitamin D supplementation than the control (M = 3.16, SE = 0.12), F(1, 88) = 4.38, p = 0.04, η_p² = 0.05.

Conclusions: Although recommendations suggest blood 25(OH)D₃ concentrations of ≥50-75 nmol/L, vitamin D status was below national recommendations. While participating in an intervention did not improve vitamin D status, it led to increased vitamin D intake, knowledge and perceived importance of supplementation.

Trial registration: ClinicalTrails.gov registration #: NCT02118129 .