The other day, I went down a rabbit hole trying to find out if there were any differences between brown and white eggs. They are laid by different types of chickens and traditionally the hens that laid brown eggs were bigger and therefore cost more to feed, hence the price difference that got passed to the consumer. According to a few sites I found, efficiencies have reduced the price difference in raising the hens but it hasn’t been passed to the consumer.
But, more interesting to me, I discovered that hens who spend time outside lay eggs that have significantly more vitamin D. Kühn et al (2014) found that free range hens laid eggs that had more than three times the amount of vitamin D.
In turns out that how cows are housed impacts the vitamin D content of their milk. Weir et al (2016) found that practices like housing cows indoors through the entire year have reduced the vitamin D content in their milk.
From a sustainability perspective, I have an interest in how we raise animals for food. There have to be many consequences of high intensity farming operations and I find this reduced vitamin D quite fascinating. I haven’t done the math, but it would be interesting to know if the supplements we have to take to make up for deficiencies could be made up by different farming practices for both animals and plants. This might require a lot more research but perhaps when I have a bit more time.