Featured article in the August, 2016 Issue of Nutrition Research Update
Vitamin D intakes are below recommendations for a large percentage of the population in the United States and Europe. As such, supplementation is often recommended to maintain serum levels of vitamin D, particularly over winter. An alternative approach is vitamin D fortification of suitable foods.
Several studies have shown that fortification of chicken feed with vitamin D3 can substantially enhance the content of D3 in eggs. For example, Mattila et al. reported vitamin D3 levels of 22-30 micrograms per 100 grams of egg yolk when birds were fed 2-6 times the normal level vitamin D3, without any negative side effects to hen health or egg quality. In the United States, the vitamin D3 level for an equivalent amount of egg yolk from a conventional egg is 5.4 micrograms.
In this present study, researchers from the University College of Cork in Ireland sought to test whether vitamin D3-enhanced eggs would enhance or maintain serum vitamin D levels in healthy older adults during the winter months. Participants were randomized to either control (2 conventional eggs/week), vitamin D3-enhanced eggs (7 eggs/week with each egg containing ~10 micrograms per egg), or 25(OH)D3-eggs, a metabolite of vitamin D3 (7 eggs/week with each egg containing ~10 micrograms per egg). Serum vitamin D levels were measured at the beginning and end of the study period.
Both groups receiving the vitamin D-enhanced eggs showed significantly higher serum vitamin D concentrations compared to control after 8 weeks with no differences between the enhanced egg groups. Further, none of the participants in either enhanced egg group had serum vitamin D concentrations <25 nmol/L, which is defined by some organizations as vitamin D deficiency.
According to the authors, “the current study, to our knowledge, is the first to investigate the effect of such vitamin D-enhanced eggs on vitamin D status in humans.” Future studies are warranted to better understand the impact of vitamin D3-enhanced eggs on serum vitamin D levels in humans of different ages over the spectrum of normal weekly egg intakes.
Hayes A, Duffy S, O’Grady M, Jakobsen J, Galvin K, Teahan-Dillon J, Kerry J, Kelly A, O’Doherty J, Higgins S, Seamans KM, Cashman KD. Vitamin D-enhanced eggs are protective of wintertime serum 25-hydroxyvitamin D in a randomized controlled trial of adults. Am J Clin Nutr. 2016;104:629-37.