Vitamin D deficiency is common in people in Canada and other northern nations. In the summer, sunlight provides vitamin D, but in the winter that vitamin comes from our diet, particularly egg yolks, oily fish and fortified dairy products. To try to increase the level of vitamin D in eggs, scientists provided supplemental UVB light to poultry layer flocks. The fluorescent tube lights were placed just above the bedding in the barns because the legs of the birds contain the highest concentrations of the precursor to vitamin D.
The project was a success. Using UVB lights for six hours a day led to an almost four-fold increase in the level of vitamin D in the eggs.
A concern was the possible effect of the light on behaviour. In the commercial poultry industry, light levels are often kept low because it is believed that lighting leads to aggression (feather-picking and subsequent cannibalism). In the study, there was no evidence of increased feather picking even at the density commonly used in furnished cage systems (i.e., 12.3 hens/m2 or 60 hens in a 4.88 m2-cage).
In an earlier study, the lead researcher found that keeping chickens outside also led to a four-fold increase in the vitamin D content of eggs. The effect depended on the amount of time the birds were outside in the sun. Layers kept inside with access to the outside had eggs with higher vitamin D concentrations than eggs from birds that never went outside, but lower than the birds that lived outside. The researchers stated, “In contrast, free-range eggs randomly acquired from supermarkets had relatively low vitamin D contents.”
An aside: Dr. Kuhn also found that dark chocolate contains high levels of Vitamin D.
Sources: Kuhn, Julia, Corinna Wassermann, Stephan Ebschke et al. 2019. Feasibility of artificial light regimes to increase the vitamin D content in indoor-laid eggs. Poultry Science. Pages 1-11. 10.3382/ps/pez234
Kuhn, Julia, A Schutkowski, H Kluge, F Hirche, GI Stangl. 2014. Free-range farming: A natural alternative to produce vitamin D-enriched eggs. Nutrition. Volume 30. Issue 4. Pages 481-484.