Collection and analysis of published scientific information as preparatory work for the setting of Dietary Reference Values for Vitamin D

Abstract

In recent years, there has been much attention for the global high prevalence of low blood concentrations of 25(OH)D, as an indicator of vitamin D status. These 25(OH)D concentrations primarily depend upon the level of sun exposure. However, also dietary vitamin D intake is of importance, especially at higher latitudes during winter. To get insight in the amount of oral vitamin D needed to achieve and maintain an adequate 25(OH)D blood concentration, the aim of this review was to systematically investigate the intake-status relationship for vitamin D under minimal endogenous vitamin D synthesis, as preparatory work for the setting of Dietary Reference Values for vitamin D. Searches were conducted in Medline, Embase and Cochrane. All published prospective cohort studies with the vitamin D intake-status relationship as the primary aim of investigation, as well as all trials, issued through 23-7-2014 and covering all ages, were included in this review, which resulted in 7,807 unique hits. Subsequently, 1,323 potentially relevant articles were identified by title and abstract screening. Hand searches led to the inclusion of 22 additional potentially relevant papers. Thus, in total, 1,345 full-text papers were screened. After full text screening, 56 articles met the predefined inclusion criteria, resulting in the inclusion of 65 studies, i.e. 57 trials and 8 prospective cohort studies, in infants, children or adults (one article corresponding to one to three studies). Two of the included studies were conducted in infants, eight in children or adolescents, and 55 in adults. The majority of the studies examined the impact of vitamin D3. Most trials studies showed a dose-response relation between vitamin D intake and status. However, as the impact of a similar dose of vitamin D on 25(OH)D concentration substantially differed across the studies, it is difficult to quantify this dose-response relationship. Therefore, the exact nature of the vitamin D dose-response relationship warrants further investigation, for instance by performing meta-regression analyses.