GSH helps the body ward off diseases associated with abnormal cell differentiation, such as those that are neurodegenerative or lead to conditions like pancreatitis or cancer.
In the first human clinical trial of its kind, scientists found that milk naturally containing only the A2 type of beta-casein protein - rather than both the A1 and A2 found in most ordinary milk - doubled the concentration of GSH in healthy adults.
Previously dairy foods have been shown to play a role in GSH synthesis, and previously, animal studies have only associated A1 protein with reductions in GSH production.
Therefore, the researchers wanted to explore the impact of the absence of A1 protein on the antioxidant's concentration
The study, which was funded by Australia’s The A2 Milk Company and published in Nutrition Journal , stated: ‘The objective of the current analyses was to elucidate the effects of consuming milk containing the A1 or A2 types of β-casein on circulating GSH concentrations in humans, using blood samples obtained in a randomized 2 × 2 cross-over study."
The team of nutrition researchers enlisted 45 subjects who, during the randomized, double-blind, controlled trial, consumed eight ounces (one cup) of milk with either A1 + A2 protein or A2 only, twice a day.
Researchers assessed differences in plasma GSH concentrations and beta-casomorphin-7 (BCM-7), a peptide produced by the breakdown of A1 protein and thought to reduce GSH concentrations.
Results showed that when consuming A2-only milk, GSH was significantly higher (4.01 ± 0.61 nmol/mL for milk containing A2 β-casein compared with 1.99 ± 0.50 nmol/mL). No significant difference between groups in BCM-7 was detected. The results were interpreted as an indication that consuming milk with A2 protein only may actually ramp up GSH production.
The study states: “The present results indicate that the consumption of milk containing only A2 β-casein was associated with greater increases in plasma GSH concentrations compared with the consumption of milk containing both β-casein types, and this was independent of a cross-over effect.”
Richard Deth, lead researcher and professor of Pharmacology in the Department of Pharmaceutical Sciences at Nova Southeastern University, said: "It was quite remarkable to find that consumption of milk containing only the A2 type of beta-casein protein produced measurably higher blood levels of the antioxidant glutathione as compared to conventional milk (which has a combination of A1 and A2 proteins).
“While we have previously shown that opiate peptide from the A1 protein in conventional milk can affect glutathione levels in cultured cells and lab animals, it is satisfying to see these effects in people.”
Through a genetic test, cows can be identified as either A1/A1 producers, A1/A2 producers or A2/A2 producers. Once identified as A2-only producers, these cows can be segregated from the herd where their milk is collected and processed separately to result in milk that only contains the A2 type of beta-casein protein.
Recent studies show that these two proteins digest quite differently from each other and, for some people, the presence of the A1 protein can result in discomfort after drinking milk.
The researchers pointed out that The a2 Milk Company was only involved with concept development and research study design, and did not contribute to data analysis or data interpretation.