Watanabe F (2007). "Vitamin B12 sources and bioavailability". Exp. Biol. Med. (Maywood). 232 (10): 1266–74. doi:10.3181/0703-MR-67. PMID 17959839.
nih.gov
ncbi.nlm.nih.gov
Subar AF, Krebs-Smith SM, Cook A, Kahle LL.(1991) Dietary sources of nutrients among US adults, 1989 to 1991. National Cancer Institute, Applied Research Branch, Bethesda, Md. 20892-7344, USA J Am Diet Assoc. 1998 May;98(5):537-47. [1]
Gille, D; Schmid, A (February 2015). "Vitamin B12 in meat and dairy products.". Nutrition Reviews. 73 (2): 106–15. doi:10.1093/nutrit/nuu011. PMID 26024497.