The mean vitamin D3 concentration of eggs in 2000/2001 and
2010 were 1.40 and 2.05 mg/100 g, respectively, but this
difference was not statistically significant due to the high
variability in vitamin D3among individual samples within each
period, as discussed below. The higher mean vitamin D content in
2010 was a result of eggs from specific suppliers having markedly
higher vitamin D content than other eggs. This higher value may
reflect the introduction into the retail food supply of eggs
produced by feeding or supplementation practices that increase
vitamin D in the yolk. Although direct supplementation of the
chicken feed with vitamin D has been used for this purpose,
vitamin D content could also be elevated as an indirect effect in
cases where fishmeal or fish oil is incorporated in poultry feed to
enhance the omega-3 fatty acid content of the yolk (Ku¨ c¸u¨ kersan
et al., 2010), if those particular fish products are high in
endogenous vitamin D.
The 25-OH-D3 content was determined only in the 2010 egg