Impact of animal and non-animal-based vitamin D fortified foods on vitamin D status: a systematic review and meta-analysis of randomised controlled trials in humans

Vitamin D deficiency is highly prevalent in the UK (1-2) . Low exposure to the sun in winter months, as well as higher risk of deficiency amongst some ethnic minority populations (1) , means that fortification of food and beverages remains an important potential route to ensure optimal vitamin D status. However, it is unclear as to whether type of fortified food affects ability to raise vitamin D status. Animal foods (e.g. dairy foods) would be expected to lead to higher vitamin D absorption than would non-animal-based foods (e.g. bread, juice), due to their higher fat content. The primary aim of this systematic review and meta-analysis was to investigate the effectiveness of animal and non-animal-based vitamin D fortified foods on raising serum 25-hydroxyvitamin D (25(OH)D). The literature search was conducted using PubMed on 23 January 2024. Inclusion criteria were as follows: data on non-pregnant/non-lactating adults or data on children, randomised controlled trial; data for 25(OH)D measurement. Initial search results retrieved 701 publications, and 593 ineligible records were removed. Next, 108 records were screened by title and abstract, with 63 records excluded, for the following reasons: off topic (n=54); pregnant or breastfeeding (n=6); non-human (n=1); preterm infants (n=1) and duration <4 weeks (n=1). After full text eligibility screening, 28 publications remained for systematic review and meta-analysis. Ethical approval was not required as this was a literature review. The end point data meta-analysis showed (for all studies combined) a significant increase in 25(OH)D (+23.4 (95% CI 17.0, 29.7) nmol/L (24 studies)). For specific food types, results were as follows: ‘animal’ +21.7 (95% CI 14.1, 29.3) nmol/L (17 studies); mixture of ‘animal’ and ‘non-animal’ +26.1 (95% CI 10.8, 41.4) nmol/L (1 study); ‘non-animal’ +28.1 (95% 12.0, 44.2) nmol/L (6 studies). Contrary to what would be expected, non-animal mode of fortification (e.g. bread, juice) had a similar effect size to animal modes (e.g. dairy), so can be considered equivalent in effectiveness in raising 25(OH)D concentration. Differences in dose, duration and population groups between the non-animal and animal modes (in terms of health and baseline vitamin D status) mean the results should be taken with caution, and future studies where these factors are standardised could be useful to provide further evidence of effectiveness.