A1 and A2 beta-casein in milk: their relationship to human health
β-casein is a 209 amino acid protein that makes up 25-35% of the total casein protein contained in milk, or roughly 2 grams per glass. Due to genetic variation, β-casein may be present as one of two major types, A1 or A2. The single difference between these two variants is an amino acid substitution at the 67th residue of β-casein. Due to this subtle difference in structure, these β-casein variants are digested differently. For A2 β-casein, “the enzymatic hydrolysis of the Ile66-Pro67 bond does not occur or occurs at a very low rate” (EFSA Scientific Report, 2009). In contrast, the digestion of A1 β-casein can produce β-casomorphin-7 (BCM-7), an exogenous opioid peptide β-casomorphin-7 (BCM-7) (Figure: 1).
Epidemiological studies suggest that A1 β-casein may be an etiological factor in certain non-communicable conditions, including type 1 diabetes and ischemic heart disease. For instance, Elliot and colleagues (2003) compared diabetes incidence in children aged 0-14 years and concluded that consumption of A1 β-casein was significantly correlated with diabetes incidence (Figure 2).
In addition, Laugesen and Elliott (2003) have shown a strong relationship between the amount of A1 β-casein consumed and heart disease mortality (Figure: 3). It has also been suggested that A1 derived BCM-7 may have other effects on human health, as its opioid activity has been linked to gastrointestinal discomfort, histamine release and other symptoms of intolerance reactions. More recently, bovine milk derived BCM-7 has also been detected in the blood stream of formula-fed infants (Kost et al., 2009).
While further research is needed to establish a cause-effect relationship between exposure to BCM-7 and the non-communicable disease conditions, the decision to recommend A2 β-casein rich milk (i.e. a2 Milk™) to clients/patients may be made on the basis of the compelling epidemiological evidence coupled with biochemical, animal and human studies (see the relevant literature sections on this website). To this end, Professor Boyd Swinburn (Professor of Public Health Nutrition, Deakin University) in his Report to the New Zealand Food Safety Authority entitled ‘Beta casein A1 and A2 in milk and human health’ (2004) stated:
“As a matter of individual choice, people may wish to reduce or remove A1 β-casein from their diet (or their children’s diet) as a precautionary measure. This may be particularly relevant for those individuals who have or are at risk of the diseases mentioned (type 1 diabetes, coronary heart disease, autism and schizophrenia). However, they should do so knowing that there is substantial uncertainty about the benefits of such an approach”.
References
Elliott R.B, Harris D.P, Hill J.P, Bibby N.J, Wasmuth H.E, (1999), Type 1 (insulin-dependent) diabetes mellitus and cow milk: casein variant consumption. Diabetologia. 42 (3), 292-296
Laugesen M & Elliott R, (2003). Ischaemic heart disease, Type 1 diabetes, and cow milk A1 betacasein. New Zealand Medical Journal. 116(1168) U295
Scientific Report of EFSA prepared by a DATEX Working Group on the potential health impact of β-casomorphins and related peptides. EFSA Scientific Report (2009) 231, 1-107
Swinburn B, (2004). Beta casein A1 and A2 in milk and human health Report to New Zealand Food Safety Authority. Prepared for New Zealand Food Safety Authority, July, 2004
Woodford K, (2007). Devil in the Milk: Illness, Health and Politics: A1 and A2 Milk, Craig Potton Publishing Wellington New Zealand. ISBN 1603581022