Milk from dairy cows has long provided a high quality source of protein and selected micronutrients as calcuim to most populations. Recently, a relationship between disease risk and consumption of specific bovine ${eta}$-casein fraction either A1 or A2 genetic variants has identified. Populations, which consume milk contain high containing high levels of ${eta}$-casein A2 variants, have a lower incidence of cardiovascular disease and type 1 diabetes. Furthermore, consumption of milk with the A2 variants may be associated with less severe symptoms of autism and schizophrenia. The mechanism of action focuses on ${eta}$-casein A1 and related forms preferentially that are able to produce a bioactive opioid peptide, ${eta}$-casomorphin-7(${eta}$-CM-7) during digestion. Infants may absorb ${eta}$-CM-7 due to an immature gastrointestinal tract. Adult, on the other hand, appear to reap the biological activity locally on the intestinal brush boarder. ${eta}$-CM-7 can potentially affect numerous opioid receptors in the nervous, endocrine, and immune system. Whether there is a definite health benefit to milk containing the A2 genetic variant is unknown and requires further investigation.