More and more, food producers are looking for ways to increase vitamin D content in foods, especially eggs. I have written about eggs and vitamin D before:
Now, Doctor Alexandra Schutkowski, working under Professor Gabriele Stangl, of the Martin-Luther-University Halle-Wittenberg in Germany have added a lot to the knowledge of vitamin D and possible vitamin D food sources from chickens.
Schutkowski A, Krämer J, Kluge H, Hirche F, Krombholz A, Theumer T, Stangl GI. UVB Exposure of Farm Animals: Study on a Food-Based Strategy to Bridge the Gap between Current Vitamin D Intakes and Dietary Targets. PLoS One. 2013 Jul 24;8(7):e69418. doi: 10.1371/journal.pone.0069418. Print 2013.
It turns out that by European Union law, the most vitamin D a chicken producer can add to their chicken fed is 3,000 IU/KG of feed, which is not enough to make much of an impact on the vitamin D content of eggs or the meat of chicken.
So, the researchers looked at alternative route to increase the amount of vitamin D in chickens and eggs. These researchers decided to use UVB irradiation on chickens to see if they could improve the vitamin D content of eggs and meat.
First, the researchers discovered that the vitamin D precursor, 7-DHC, is almost entirely in the skin of the legs of chickens. The content of 7-DHC in the skin of chicken legs was more than 190 times higher in the legs than the skin of any other part of the chicken, including the comb. This led them to irradiate the legs of chickens, placing their lights at the side of the cages rather than on top.
The researchers than divided the chickens into four groups. The first group got no vitamin D in feed and no UVB; the second got 3,000 IU/KG in feed but no UVB; the third got no vitamin D in feed but did get UVB; and the fourth group got both vitamin D in feed and UVB.
They found the following:
- The serum 25(OH)D levels of the UVB irradiated chickens were the same as the chickens that got 3,000 IU/KG in feed.
- Surprisingly, even though 25(OH)D levels were the same in the two groups of chickens, the yolks of the chickens getting UVB had seven times more D3 (cholecalciferol) in them than did the chickens getting the 3,000 IU/KG of feed but no UVB.
- The meat of the chickens getting UVB had 5 times more cholecalciferol (D3) in them than did the chickens getting D3 in feed but no UVB.
- The 25(OH)D content of eggs was about the same for UVB treated chickens compared to feed only chickens, but the total amount of D3 in the eggs of UVB chickens was much more than the total amount of 25(OH)D in eggs of feed only chickens (30 ug/100 grams D3 versus 3 ug/100 grams of D3 in dried yolk.) That is, the UVB chickens had ten times more total D3 metabolites in them than did the 3,000 IU/KG of feed chickens despite the serum 25(OH)D of the two groups of chickens being about the same.
- They also showed that UVB irradiation of chickens is capable of optimizing laying performance, eggshell quality, and bone stability in hens compared to the chickens receiving no vitamin D3 in their diet.
The authors said:
“An interesting finding of this study was that UVB exposure could increase vitamin D3 and 25(OH)D3 concentrations in egg yolk and muscle, whilst an oral administration of vitamin D3 mainly increased 25(OH)D3, but had minor impact on vitamin D3 in egg yolk and muscle. . . In conclusion, the current study shows that UVB exposure of chickens that ensures irradiation of the whole body, including legs, is highly effective in increasing the vitamin D concentration in eggs, and meat. We therefore consider UVB treatment of farmed animals as an effective and novel approach for ‘‘bioaddition’’ of foods with vitamin D. Considering the option that free-ranged chickens are still exposed to natural sun light, free-range husbandry could become a cheap alternative to the artificial UVB irradiation to produce vitamin D3 fortified eggs.”
You may be thinking, do free-range chickens then have more vitamin D in their eggs compared to non-free-range chickens’ eggs? As the legs of chickens are underneath its body, I am not sure free-range chicken eggs will have as much vitamin D as do chickens irradiated from the side with UVB light. However, it will be a lot more D3 than the eggs that come from the usual indoor commercial egg factories. It will be interesting to see if egg manufacturers explore this UVB method, if it’s cost effective and if consumers want vitamin D-rich eggs.