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I.J.S.N., VOL.7 (1) 2016: 01-05 ISSN 2229 –6441
1
Review Article
A1 AND A2 MILK & ITS IMPACT ON HUMAN HEALTH
1Prasanta Boro, 2Binoy Chandra Naha, 3Deep Prakash Saikia & 4Chandra Prakash
ICAR-Indian Veterinary Research Institute, Izatnagar, Bareilly, U.P-243122
1PhD Scholar, LPM Section, ICAR-IVRI
2PhD Scholar, Animal Genetics Division, ICAR-IVRI
3PhD Scholar, Veterinary Biotechnology Division, ICAR-IVRI
4MVSc Scholar, Animal Genetics Division, ICAR-IVRI
*Corresponding author email: boroprasanta99@gmail.com
ABSTRACT
Most common economically important milk constituents traits include fat, protein, SNF, lactose and ash. These
characteristics and associated benefits have made milk an important part of the diet. Amongst the milk constituents, beta-
casein has gained importance and popularity amongst the health conscious people due to its recent health related issues.
Beta casein composition of milk and milk products has become an important economic trait of dairy animals. Our
indigenous dairy animals produce A2 milk and India is endowed with rich A2 dairy animals since our civilizations,
protecting the masses from ill effects of A1 milk. It is a matter of great concern for the health of people in India. There i s a
urgent need to go through our breeding policies to stop producing A1 milk.
KEYWORDS:A1 and A2 Milk, Human health
INTRODUCTION
Milk is the complete food for the infant. It contains the
essential micro-nutrients needed for growth and
development of human health as well as for the neonate
animal. In USA, Australia, New Zealand and other
developed countries, people use to consume milk
according to their needs and use milk like A2 milk, since
A2 milk is harmless whereas A1 milk is harmful for
health. So, our future breeding policies for dairy animals
should be done in a systematic manner, keeping an eye on
producing clean and healthy milk which is none other than
A2 Milk.
What actually is A1 and A2 milk?
Milk contains about 85% water. The remaining 15% is the
milk sugar lactose, protein, fat and minerals. Beta-casein is
about 30% of the total protein content in milk. A2 milk is
the milk that contains only the A2 type of beta-casein
protein whereas A1 milk contains only A1 beta casein or
A1A2 type variant. A1 protein variant is commonly found
in milk from crossbred and European breeds of cattle. A2
milk is found basically in indigenous cows and buffaloes
of India (Asia as a whole). A2 milk is branded by the A2
Milk Company like A2 Corporation and sold mostly in
Australia, New Zealand, United Kingdom and other
developed countries.
History of A1 and A2 Milk
A2 beta-casein is the beta-casein from cows that have been
produced since before they were first domesticated over
10,000 years ago. It has no known negative effects on
human health. In the past few thousand years, a natural
mutation occurred which has resulted in a proportion of
cows of European breeds producing a casein variant called
A1 beta-casein. Slowly, these protein variant became
dominant in milk which producing A1 milk. The gene
encoding beta-casein was changed such that the 67th
amino acid in the 209 amino proteins was switched from
proline to histidine. This new kind of beta-casein that was
created is known as A1 beta-casein which is found in the
milk of many crossbred cows such as Holstein, jersey and
Friesian.
Basic genetics of A1 and A2 milk
The A1/A2 status of a cow is determined by a pair of
genes on the sixth chromosome (Rijnkels, 2002). There
are two major alleles of the gene i.e A1 and A2 beta-
casein alleles. A cow carries two copies of the beta-casein
gene; she can carry either of A2A2 (homozygous), A1A2
(heterozygous) or A1A1 (homozygous) alleles. Neither
allele is dominant over the other rather; they are co-
dominant i.e. additive in their effect. Therefore, an A1A2
cow will produce A1 and A2 beta-casein in equal
amounts. An A2A2 cow will only produce A2 beta-casein
and an A1A1 cow will only produce A1 beta-casein. The
Northern European breeds of cows such as the Friesian
and Holstein carry the A1 and A2 allele at about equal
levels. The Southern European breeds and the Jersey carry
the A1 allele at about 35% and 2/3 of A2. Exceptionally,
Guernsey breed appears to carry the A1 allele at less than
10% and the Scottish Ayrshire breed appears to be well
over 50%. In addition, individual herds may carry the
allele at levels that are quite different to the average for the
breed. If a cow is A2A2 then she is guaranteed to pass on
the A2 allele to her progeny. Similarly, an A1 cow is
guaranteed to pass on the A1 allele. For an A1A2 cow
there is a 50% chance of passing on either of the allele.
Status of Milk protein variants in Cattle
Researches conducted on indigenous cows (Zebu type),
buffaloes and exotic cows (Taurine type) have revealed
A1 and A2 Milk: Its impact on human health
2
that A1 allele is more frequent in exotic cattle (A1 milk)
while Indian native dairy cows and buffaloes have only A2
allele and hence are a source for safe milk i.e A2 milk
(Mishra et al., 2009). The A2 allele gene in Indian milk
breeds of cows and buffaloes are 100% (Red Sindhi,
Sahiwal, Tharparkar, Gir and Rathi), other Indian breeds
used for farming, is around 94 per cent (Joshi, 2011) and
while in foreign breeds (HF and Jersey), it is around 60
per cent (NBAGR, 2011). A1 β-casein is absent in the
milk of pure Asian and African Cattle (Ng-Kwai-Hang
and Grosclaude, 2002). So, our indigenous cows and
buffaloes produce A2 milk.
1. Allelic and genotypic frequency of Beta casein gene across the Indian cattle breeds (Mishra et al., 2009)
Sl. No.
Cattle breeds
Allelic Frequency
Genotype Frequency
A1
A2
A1A1
A1A2
A2A2
1
Sahiwal
0
1
0
0
1
2
Red Sindhi
0
1
0
0
1
3
Tharparkar
0
1
0
0
1
4
Gir
0
1
0
0
1
5
Kangayam
0
1
0
0
1
6
Nimari
0
1
0
0
1
7
Red Kandhari
0
1
0
0
1
8
Amritmahal
0
1
0
0
1
9
Malvi
0
1
0
0
1
10
Kankrej
0
1
0
0
1
11
Hariana
0
1
0
0
1
12
Rathi
0
1
0
0
1
13
Mewati
0
1
0
0
1
14
Malnad Gidda
0.096
0.904
0
0.191
0.809
15
Kherigarh
0.109
0.891
0
0.218
0.783
2. Occurance of Beta casein gene variants in various cattle breeds and countries (Kaminiski et al., 2007)
Sl. No.
Cattle breeds
Countries
Frequency of Beta casein alleles
References
B
A1
A2
1
Jersey
Germany
0.186
0.093
0.721
Ehrmann et al., 1997
Denmark
0.350
0.070
0.580-360
Bech et al., 1990
New Zealand
-
0.123
0.591
Winkelman and
Wickham, 1997
USA
0.290-
0.370
0.090-
0.220
0.490-540
Enennam et al.,1991
2
HF
Norway
-
0.400
0.490
Lien et al., 1993
3
Guernsey
USA
0.010
Swaissgood, 1992
4.
Brown Swedish
Germany
0.170
0.108
0.705
Ehrmann et al., 1997
5.
Simmental
Croatia
0.150
0.190
0.630
Curik et al.,1997
6
Ayrshire
UK
0-0.003
0.006
0.004
Swaissgood, 1992
3. Allelic and genotypic frequency of Beta casein gene across the Indian Buffalo breeds (Mishra et al., 2009)
Sl. No.
Buffalo breeds
Allelic Frequency
Genotype Frequency
A1
A2
A1A1
A1A2
A2A2
1
Murrah
0
1
0
0
1
2
Mehsana
0
1
0
0
1
3
Marathwada
0
1
0
0
1
4
South Kanara
0
1
0
0
1
5
Manipuri
0
1
0
0
1
6
Assamese Swamp
0
1
0
0
1
7
Nilli-Ravi
0
1
0
0
1
8
Pandharpuri
0
1
0
0
1
Milk protein and BCMs
Bovine milk protein is composed approximately of 80%
casein and 20% whey (Shah, 2000; Niki et al., 1994;
Martien et al., 1994). But according to some researchers
whey proteins constitute about 14% (McLachlan, 2001;
Roginski, 2003). It contains four components namely αs1
(CSN1S1, 39–46%), αs2 (CSN1S2, 8–11%), β(CSN2,
25–35%), and κ(CSN3, 8–15%) of total caseins (Eigel et
al., 1984; Roginski, 2003,Rijnkels, 2002)whereas human
milk casein is composed of primarily β, and κ1.β-casein
is the second most abundant protein and crucial for casein
micelle structure. Beta-casein is 30% of the total protein
content in cow's milk. The polymorphic status of bovine β-
casein is confirmed, and till date 13 allelic variants have
been identified (Kaminski et al., 2007). Amongst these,
A1 and A2 variants are reported to be the most common
allelic variants of β-casein in dairy cattle (Farrell et al.,
2004). The polymorphic nature and its association with
I.J.S.N., VOL.7 (1) 2016: 01-05 ISSN 2229 –6441
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milk, fat and protein yield attracted several efforts in
evaluating this locus as a potential dairy trait marker
(Ikonen et al., 1999; Caroli et al., 2004; Kucerova et al.,
2006). Consumption of milk of certain breeds of cow,
buffaloes, sheep and goat may result in the release and
possible absorption of bioactive peptides like BCMs.
These peptides yielded by the digestion of β-casein have
opioid effects similar to morphine, and so named β-
casomorphins (β-CMs). The β-CMs have unique structural
structural features that impart a high and physiologically
significant affinity with the binding sites of endogenous
opioid receptors (Meisel and FitzGerald, 2000). Of the
protein variants A1 betacasein yields BCM-7 whereas A2
betacasein does not give rise to BCM-7 upon digestion
(Woodford, 2006; Bell et al., 2006). β-CM-7 has been well
established as a potent bio-active peptide with opioid
activity.
Mechanism of BCM-7 generation in the Small intestine
The A1 and A2 variants of bovine β-casein differ at amino
acid position 67 with histidine in A1 and proline in A2
milk. This polymorphism leads to key conformational
changes in the secondary structure of expressed β-casein
protein (Elliot et al., 1999; McLachlan, 2001). Due to
presence of histidine at amino acid 67 position, digestion
of A1 β-casein milk releases a 7 amino acid bioactive
peptide called beta-casomorphin 7 (BCM-7) in small
intestine, while proline in A2 milk at 67 position prevents
the split at this particular site and generates peptide BCM-
9 (Roginski, 2003; Kostya et al., 2004). It is believed that
generation of BCM-7 is the major causative factor
associated with A1 milk related health disorders.
However, A2 β-casein not been linked to any of such
health issues (Kaminski et al., 2007).
Impact of A1 and A2 milk on human health
Milk from dairy cows is providing a high quality source of
protein and an essential micronutrients like energy,
calcium, magnesium and phosphorus to human beings
since long time (Bell et al., 2006). A significant
relationship was observed between bovine milk protein
consumption and the incidence of type 1 diabetes and
CVD (McLachlan, 2001; Laugesen and Elliott, 2003;
Elliott et al., 1999; Thorsdottir et al., 2000, Virtanen et al.,
2000; Monetini et al., 2002; Birgisdottir et al., 2002),
arteriosclerosis (Tailford et al., 2003). Besides,
neurological disorders such as schizophrenia and autism
(Woodford, 2006), and sudden infant death syndrome
were also appeared to be known to potentiated by milk
(Sun et al., 1999; Sun and Cade, 1999; Sun et al., 2003).
The relationship between disease risk and bovine milk
consumption is the focus of this review with special
emphasis to A1 and A2 hypothesis.
In many of the medical literature we get to know the link
between the development of ischemic heart disease (CVD)
and specific milk protein intake (McLachlan, 2001;
Laugesen and Elliott, 2003; Tailford et al., 2003). Besides,
some populations such as the Masai (East African) and
Samburu (Northern Keyan) had virtually no heart disease
despite consuming a diet rich in animal milk. But that milk
fortunately came from Zebu cattle, which is a breed that
carries the A2 allele exclusively (McLachlan, 2001).
Western countries, which had similarly high bovine milk
consumption from predominantly the Holstein breed,
jersey and other breeds had a greater incidence of CVD
than nations with low milk consumption. It is so because
people of small nations consume fortunately A2 milk. But
epidemiological analyses concerning the two alleles of β-
casein and the incidence of CVD underscores the apparent
relationship between the risk of chronic disease and milk
protein variant intake (McLachlan, 2001; Laugesen and
Elliott, 2003). Above all many researchers have claimed
the relationship of A1 milk with many human diseases like
CVD, autism, schizophrenia etc (Woodford, 2011, Mishra
et al., 2009).
The Food and Agriculture Organisation (FAO) (2012) has
reported increase in many chronic diseases arising out of
milk. These diseases if studied thoroughly can be
alleviated by improving the health benefiting milk
components. The β-casein composition of the protein
fraction has become of special interest recently because of
a possible relationship between β-casein genotype and the
health of population of consumers. Genetic variants in
bovine β-casein gene (A1 and B) release a bioactive
peptide, β-casomorphin-7(BCM-7) upon digestion,
responsible for many human disorders like Type 1
diabetes, autism, schizophrenia and heart diseases but A2
milk does not cause such type of illnesses (Keith
Woodford, 2007; Mishra et al., 2009; Sodhi et al., 2012).
Infants may absorb β-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. Β-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 unlike harmful effects of A1 milk.
With the increasing intake of dairy products, the
consumption of other essential nutrients such as zinc,
vitamin A, magnesium, folate, and riboflavin are also
increasing (Weinberg et al., 2004). However, we are able
to get only about 700 mg of calcium per day, which comes
primarily from dairy products (Weinberg et al., 2004;
Ervin et al., 2004). This amount is against the
recommended amount of 1,000–1,500 mg (NIH
Consensus Development Conference, 1994). Most other
food sources contain low concentrations of calcium.
Calcium content of milk, may reduce the risk of
osteoporosis and colon cancer (Heaney et al., 1999; Birt et
al., 1999) and including milk in the diet may promote
weight loss (Phelan et al., 2003). The ideal calcium to
magnesium ratio for the human body should be 2:1. The
A1 milk's ratio is 10:1. By relying on A1 cow's milk for
calcium, we will have magnesium deficiency and
imbalance, but A2 milk does not cause such imbalances.
Magnesium relaxes us, helps improve digestion, is anti-
inflammatory in action, involved in nerve and muscle
function, de-toxifier, increases alkalinity of the blood and
flexibility of the tissues. Magnesium is required for the
body to produce and store energy. Without magnesium
there is no energy, no movement, no life. So, A1 milk will
lower magnesium levels whereas A2 milk does not.
The inflammation from A1 milk casein causes lymphatic
congestion and metabolic suppression. A1 milk worsens
acne, eczema, upper respiratory infections, asthma and
allergies. It causes digestive problems, not because of the
lactose but because of massive histamine release from
casomorphin. Ear infections, bronchitis, tonsillitis are
A1 and A2 Milk: Its impact on human health
4
driven by A1 casein. A1 milk casein causes endometriosis
because of its inflammatory and immune-disruptive effect.
Endometriosis is a gynecological condition in which cells
from the lining of the uterus (endometrium) appear and
flourish outside the uterine cavity, most commonly on the
membrane which lines the abdominal cavity. Many
women with infertility may suffer from endometriosis and
other reproductive complications.
CONCLUSION
We can now conclude that we should drink A2 milk only
as it prevents us from milk related health complications
especially from A1 milk. More research is also required to
prove the reality of the hypothesis of A1 and A2 milk. In
this aspect, Government’s support is needed to accomplish
the above anomalies of milk quality and standards to
improve the health of the people.
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