https://goodness-exchange.com/cod-vikings-vitamin-d/
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2258476/
https://www.westonaprice.org/did-cod-liver-oil-contribute-to...
I was thinking about this: https://en.wikipedia.org/wiki/Cod_liver_oil
https://goodness-exchange.com/cod-vikings-vitamin-d/