Iron content of eggs
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Iron Content in Eggs: Baseline Levels and Distribution
Eggs are recognized as a good source of dietary iron, with most of the iron found in the yolk rather than the white. Typical iron concentrations in egg yolk range from about 62 to 71 micrograms per gram (µg/g) under standard feeding conditions, while the white contains much less iron 12. The distribution of iron between yolk and white is not significantly affected by storage, and individual birds or breeds do not show large differences in baseline iron content .
Dietary Iron Supplementation and Egg Iron Enrichment
Research consistently shows that the iron content of egg yolks can be increased by supplementing the hens' diet with various forms of iron. Supplementation with organic iron compounds, such as iron-soy proteinate, iron-methionine chelate, iron glycine chelate, and iron amino acid complexes, has been shown to raise the iron content in egg yolks by 15–17% compared to control diets 134568. For example, adding 2.5 g/kg of a mineral premix containing iron to the diet resulted in a 15.7% increase in yolk iron content after six weeks . Similarly, supplementing with 100 ppm iron as iron-soy proteinate for five weeks increased yolk iron by 16.6% .
Both organic and inorganic iron sources (such as FeSO4) are effective, but organic forms may be slightly more efficient at enriching egg yolk iron and improving egg quality 568. The optimal supplementation level varies, but studies suggest that 45–120 mg/kg of organic iron in the diet is effective for maximizing yolk iron without negatively affecting egg quality or hen health 568.
Factors Affecting Iron Bioavailability in Eggs
The bioavailability of iron from egg yolk is relatively high, especially when consumed with vitamin C (ascorbic acid), which enhances iron absorption. In animal studies, the biological value of egg yolk iron was found to be 85% that of ferrous sulfate, a standard reference for iron bioavailability, and equivalent when ascorbic acid was present . Cooking eggs and the age of the laying hen can also influence iron availability. Cooked egg yolks and eggs from older hens tend to have higher available iron content, likely due to changes in yolk protein composition, particularly a decrease in phosvitin, which binds iron tightly and reduces its availability .
Impact on Egg Quality and Hen Health
Supplementing hen diets with iron, especially in organic forms, generally does not negatively affect egg quality or hen performance when used at recommended levels. In fact, some studies report improvements in egg weight, shell color, and internal quality measures such as Haugh unit 358. However, excessive iron supplementation can reduce egg production and quality, so optimal dosing is important .
Conclusion
Eggs naturally contain a moderate amount of iron, primarily in the yolk. The iron content of eggs can be significantly increased by supplementing the hen's diet with organic or inorganic iron sources, with organic forms often providing additional benefits for egg quality. The bioavailability of egg iron is high, especially when eggs are cooked or consumed with vitamin C. These findings support the potential for producing iron-enriched eggs as a functional food to help address dietary iron deficiencies.
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