http://www.thepaleomom.com/2012/04/why-everyone-should-be-eating-organ.html
Liver is known to be one of the most concentrated sources of vitamin A of any foods. In addition to containing dozens of important vitamins and minerals, it is an outstanding source of Vitamin D, Vitamin B12 and iron, which is in a form that is particularly easily absorbed and used by the body. Kidney is particularly high in Vitamin B12, selenium, iron, copper, phosphorus and zinc. Even though heart is technically a muscle, it also is also a superfood. Heart is a very concentrated source of the supernutrient, Coenzyme Q10 (CoQ10), contains an abundance of Vitamin A, Vitamin B12; folic acid, iron, selenium, phosphorus and zinc, and is the number one food source of copper. Heart also contains twice as much collagen and elastin than regular meat (which means it is rich in the amino acids glycine and proline), which are essential for connective tissue health, join health and digestive health (see The Health Benefits of Bone Broth).
Liver is known to be one of the most concentrated sources of vitamin A of any foods. In addition to containing dozens of important vitamins and minerals, it is an outstanding source of Vitamin D, Vitamin B12 and iron, which is in a form that is particularly easily absorbed and used by the body. Kidney is particularly high in Vitamin B12, selenium, iron, copper, phosphorus and zinc. Even though heart is technically a muscle, it also is also a superfood. Heart is a very concentrated source of the supernutrient, Coenzyme Q10 (CoQ10), contains an abundance of Vitamin A, Vitamin B12; folic acid, iron, selenium, phosphorus and zinc, and is the number one food source of copper. Heart also contains twice as much collagen and elastin than regular meat (which means it is rich in the amino acids glycine and proline), which are essential for connective tissue health, join health and digestive health (see The Health Benefits of Bone Broth).