Mining milk for its therapeutic benefit

Monday 21 February 2011 sees the start of National Dairy Week, which promotes the value of milk and dairy foods in a healthy balanced diet.

As well as being a complete food for newborns, milk has long been credited with a pivotal role in adult dental and bone health, largely because of its nutrition content (eg, calcium).

But more recent evidence, summarised in a paper in the Journal of Dairy Research, has revealed that milk contains many components associated with health benefits beyond those expected based on its nutritional content alone.

In the past couple of decades, much research has concentrated on the therapeutic effect of milk proteins. For example, whey protein has been investigated for suppression of tumour development. It is also attracting interest as an ingredient for weight management.

The membrane surrounding milk fat droplets, which is itself composed of layers of lipids and protein, is also being investigated for therapeutic potential. One of its proteins, fatty acid binding protein, appears to inhibit some breast cancer lines, while another inhibited Helicobacter pylori in an animal study.

Recently, too, the basic protein fraction in milk has been shown to have a direct effect on strengthening bone in human volunteers.

Bioactive peptides from milk are a subject of intense study, particularly those with an antihypertensive effect. Milk fermentation has been used to release peptides with angiotensin-converting enzyme activity, and several have found their way into commercial products.

Milk has also been found to contain antithrombotic peptides, largely through enzymatic hydrolysis of K-casein. K-casein is structurally similar to the gamma chain in human fibrinogen, leading to the suggestion that both may have evolved from a common ancestor during the past 450 million years.

Milk is also a rich source of antimicrobial proteins and peptides. For example, bovine lactoferrin has antiviral activity against human immunodeficiency virus and human cytomegalovirus.

Several studies show that infants who have been breast-fed as babies display some higher intelligence skills than formula-fed babies. In a study of infants who died from sudden infant death syndrome, the brain frontal cortex grey matter of breast fed infants was found to be higher in sialic acid, an oligosaccharide found in human and bovine milk.

A study in pigs has provided some evidence that sialic acid can improve brain development, learning and memory.  

A range of milk lipids is also being investigated, of which conjugated linoleic acid (CLA) is a key example. CLA is made in ruminant animals through conversion of linoleic acid. Several in vitro studies have demonstrated that it has effects against cancer, hypertension, atherosclerosis and diabetes as well as the ability to improve immune function. Efforts are being made to increase the CLA content of bovine milk to generate dairy products of enhanced functional value.

The dissection of milk into various bioactive components shows promise in terms of potential therapeutic benefits, but these intriguing effects need to be proved in humans as well as in the laboratory as many of the findings to date have come from in vitro studies. But it is not surprising that milk should have these properties given that it is the sole food for all newborns during their early development.

Now research is moving beyond the components of milk to milk genomics (ie, the genes that encode the composition of milk) in the hope that such an approach will help to define the biology of mammalian nutrition.

The science in milk is as yet an unfinished story and will undoubtedly be put to increased commercial use in the future.