Health implications of milk containing beta-casein with the A2 genetic variant

Crit Rev Food Sci Nutr. 2006;46(1):93-100. doi: 10.1080/10408390591001144.


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

Publication types

  • Review

MeSH terms

  • Adult
  • Animals
  • Cardiovascular Diseases / epidemiology*
  • Caseins / adverse effects*
  • Caseins / genetics*
  • Cattle
  • Diabetes Mellitus, Type 1 / epidemiology*
  • Genetic Variation / genetics*
  • Humans
  • Infant
  • Milk / adverse effects*
  • Rabbits
  • Rats
  • Risk Factors


  • Caseins