Impact of Milk Derived β-Casomorphins on Physiological Functions and Trends in Research: A Review

β-Casomorphins are a group of opioid peptides released during gastrointestinal digestion or food processing from the β-casein of milk protein. Consequently, milk can be divided into A1 and A2 "like" groups depending upon the presence or absence of proline or histidine at the 67th position of β-casein. A1 "like" milk is postulated to be a source of BCM-7 as histidine allows the cleavage at this position, while A2 "like" milk has proline that resists the hydrolysis. On one hand, BCM-7 has been implicated as a risk factor for cardiovascular diseases, type I diabetes, and neurological disorders. On the other hand, various physiological effects of these peptides have also been documented, i.e., secretion of mucus, increased activity of superoxide dismutase and catalase, increased levels of prolactin, and analgesic role. In addition, many evidences correlate these peptides with various immunological functions, such as development of innate immunity, lymphocyte proliferation and cellular immunity, role in autoimmune diseases, histamine release, and allergy. In conclusion, the role of β-casomorphins in physiological functions remains controversial and more research with improved diagnostic techniques is needed to unravel the mechanism and study physiological functions of β-casomorphins. Thus, health-related aspects of β-casomorphins (positive, negative, and immunological impacts) have been comprehensively reviewed in this article.