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Milk in the dock (Image: Foodcollection/Getty)

ELTON John sported one. So did Taylor Swift, David Beckham and Heidi Klum. For many years, a milk moustache was touted as a badge of good health, confirmation that you were getting the essential calcium, protein and other goodies packed into a fresh glass of moo-juice. The advertising campaign behind these images, “Got Milk?”, was one of the most influential ever in the US.

Yet today, many households are going off milk. Around 15 per cent of people in Europe now avoid dairy products for medical or lifestyle reasons, and the market for dairy-free alternatives is growing rapidly.

For many, the move away from milk is rooted in concerns about lactose intolerance, or the view that plant-based alternatives are healthier. Recent research suggesting that milk might actually be bad for your bones has only further soured our relationship with it.

So what’s the skinny on milk: is it an elixir or a poison? And if you have to avoid cow’s milk, what should you drink instead?

The ability to consume large amounts of milk in adulthood is thought to have arisen around 7000 years ago. The main sugar in milk is lactose, which can only be absorbed by the gut if broken down into simpler sugars by the enzyme lactase. All baby mammals produce lactase, but usually switch off making it around the time they start eating solid food. About 35 per cent of humans, however, have a genetic mutation that means they continue to produce lactase, and so can drink milk in quantity throughout life.

It’s easy to see how this mutation would have been beneficial, as milk is a rich source of fats, proteins and other nutrients. “It improved health in general, and this led to more successful reproduction,” says , who studies nutrition and human health at the University of Reading, UK.

In people who lack lactase, lactose passes into the colon where it feeds bacteria that generate gas and fluid, resulting in painful bloating, cramps and diarrhoea – a condition known as lactose intolerance or malabsorption. In China and South-East Asia, more than 90 per cent of people are thought to be lactose intolerant (see map), compared with between 2 and 20 per cent of those of northern European descent. However, its incidence is hard to pin down as many people rather than taking a clinical test (see “Are you lactose intolerant?“).”I think that people are a little too quick to self-diagnose bowel conditions like lactose intolerance these days because so much information is out there about them,” says , a spokeswoman for the British Dietetic Association. “The market for alternative milk products has also gone crazy, so people probably think lactose intolerance must be on the rise; it’s not.”

Appealing alternatives

Lactose intolerance aside, people might be opting for milk alternatives for other reasons. In recent years consuming milk has been linked to cancer, diabetes, asthma, acne and even weak and fragile bones. The alternatives, meanwhile, can be low in calories and fats, and often have the added appeal of new and interesting flavours.

The switch away from milk throws the spotlight on to one essential mineral we get from it: calcium. It helps build healthy teeth and bones, and plays a crucial role in blood-clotting, nerve signalling and muscle contraction. Milk and dairy products are among the best sources, but calcium is also found in green leafy vegetables, soya beans and nuts. Without enough calcium, children risk stunted bone development and some adults are placing themselves at greater risk of osteoporosis and bone fractures, either now or in the future.

Yet in many Western countries, milk consumption has been falling since the 1970s, and dairy consumption is well below recommended levels. In 2010, the official Dietary Guidelines for Americans recommended 2.5 cup equivalents (about 0.6 litres) of dairy products per day for children aged 4 to 8, and 3 cups for anyone over 8. Average consumption for adults in the US is .

A bucketful of goodness? Depends who you ask (Image: G M B Akash/Panos Pictures)

“My biggest worry about the current trend for ditching cow’s milk relates to bone development in children and adolescents, and its long-term effect on bone strength in postmenopausal women,” says Givens. Teenage girls, in particular, tend to lack the calcium they need in their diet (see “Calcium concerns”), and this could boost their future risk of osteoporosis, as they grow.

Not everyone is convinced that there is always a link between milk consumption and bone health, however, and new findings hint that for adults, drinking too much milk might have a dark side. Last year, at Uppsala University in Sweden and his colleagues published a paper which challenged the dogma that high milk consumption results in stronger bones. They followed 61,433 women over 20 years and 45,339 men for 11 years, and found that the more cow’s milk people said they drank, the more likely they were to experience a bone fracture during the study period. The risks were greatest for women: those who drank three or more 200-millilitre glasses of milk per day had a 16 per cent higher chance of sustaining a bone fracture than those who drank only one. What’s more, those who consumed more milk were also more likely to die during the study; the women who drank three or more glasses had double the chance of dying as those who drank one (BMJ, ).

“Not everyone is convinced of the link between milk and bone health”

Michaëlsson’s theory is that galactose, one of the constituent sugars of lactose, is to blame. When lab animals are fed modest amounts, equivalent to one to two glasses of milk per day for humans, galactose triggers premature ageing and shortens life expectancy due to . Theoretically, this could lead to bone loss and muscle damage – which would boost fracture risk – and also contribute to other diseases of ageing, which might explain the increased mortality that Michaëlsson recorded.

Although other studies have similarly , there isn’t enough evidence yet to suggest the general population should change their dietary pattern, Michaëlsson says, but it is an area which needs more investigation. As for the advice to drink two to three glasses of milk per day for healthy bones, he says such government messages are based on studies of the maximum amount of calcium that can be forced into bones over a short period of time. “It is a long way to extrapolate these studies to real life,” he says.

Other concerns centre around the hormones in milk, such as insulin-like growth factor (IGF-1). There are claims that they could boost the risk of cancer and diabetes, not to mention triggering acne and precocious puberty. Cows given recombinant growth hormone, as is allowed in some areas, produce milk with elevated levels of IGF-1.

A key proponent of this theory is Bodo Melnik at the Osnabrück University in Germany. He suggests that IGF-1, plus some of the amino acids and fragments of genetic material in milk, all feed into a cellular signalling pathway that essentially takes the brakes off cell growth, boosting the risk of cancer and other diseases. Constantly high levels of IGF-1 could also , resulting in type 2 diabetes. “Milk is not just a nutrient. It is a complex, bioactive substance honed by evolution to promote growth at the cellular level,” Melnik says.

Melnik’s ideas are controversial. , an IGF-1 researcher at the University of Bristol, UK, says that levels of the hormone in cow’s milk are not an issue in themselves, but milk does stimulate production of the same hormone by our pituitary gland. “The more milk you drink, the more IGF-1 you will have in your body,” he says.

IGF-1 certainly stimulates cellular growth, and could help , although the protein and calories in milk would also play a part. But Holly agrees with Melnik that too much IGF-1 in later life could be a bad thing. His main concern is that drinking a lot of milk as an adult might boost growth of subclinical cancers, although the evidence is mixed.

Reviews by both the World Cancer Research Fund and the American Institute for Cancer Research have concluded that there is a probable link between dairy product consumption and prostate cancer, but also that milk and dairy consumption probably protects against colorectal cancer and .

“Overall the evidence from long-term cohort studies is much stronger for the protective effect of milk for colorectal cancer than for the increased risk of prostate cancer, ” says Givens, “but we should not ignore it.” Studies into the effects of milk on diabetes have too, and diabetes rates in the West have risen at the same time as milk consumption has dropped, casting doubt on any link.

So why is it so difficult to get a clear-cut answer on the health effects of milk? One reason may be that milk itself is so complex. It promotes IGF-1 production, and it contains whey proteins and protein fragments called peptides, all of which, like calcium, have signalling roles. A protein called lactoferrin, for instance, plays a crucial role in iron absorption and exerts antioxidant and anti-carcinogenic effects. Meanwhile, peptides derived from another milk protein called casein may influence the behaviour of immune cells, and to the gut.

Then there’s the question of what we consume alongside milk as part of our complex diet. One reason why milk and other dairy products may protect against colorectal cancer is because calcium seems to bind to and neutralise carcinogenic substances in meat.

This interplay with other aspects of our diet could benefit heart health too. A meta-analysis of 15 studies by Givens and his colleagues concluded that high consumers of milk and dairy have than low consumers. Again, the reason could be calcium, which binds to dietary fats in the intestines and also to some of the bile acids that help to digest fat, preventing its absorption by the body.

Drink up: children who drink milk tend to be taller (Image: Kurt Hutton/Getty)

But of course there are other sources of calcium in the diet, such as nuts and vegetables, not to mention other dairy products. One problem with many of these studies is that they rarely distinguish between milk, cream and butter on one hand and fermented dairy products like cheese, soured milk and yoghurt on the other. Cheese and yogurt are low in lactose and galactose, whereas milk contains high levels of these sugars; cheese also contains around six times as much calcium weight for weight as whole milk. Although Michaëlsson found an increased risk of mortality associated with milk consumption, when he looked at big consumers of fermented milk products, it was a different story. “We saw some reduction in fractures and mortality,” he says. These findings suggest it might be wise to get some of the protein, vitamins and minerals milk provides from other healthy sources, like yogurt, nuts and seeds.

You can’t readily pour these into your tea or cereal, though. So with the health benefits of milk still under scrutiny, how do the fashionable dairy-free alternatives stack up?

Just over 3 per cent of cow’s milk is protein, and it’s also an excellent source of vitamin D and iodine – essential for healthy bones and the production of thyroid hormones respectively. That’s in marked contrast to some plant-based substitutes, which are made by grinding plant material, adding water to make a slurry and then straining it.

Plant milks are often perceived as healthier than cow’s milk, but in reality their , says at the University of Copenhagen in Denmark, who recently published a review on the subject. “Apart from soya milk, most of them are quite low in protein, and there are some extreme cases: rice milk has just 0.1 per cent protein,” she says (see “The white stuff”).

Plant-based milks may have other benefits, however. Many are low in calories, which could be helpful for weight loss. On the other hand, plant milks tend to be low in calcium and vitamin D – unless they are fortified. Even then there is evidence to suggest that this doesn’t confer the same health benefits as calcium from milk. The calcium in dairy products is more similar to the calcium compounds in the body so it’s more readily incorporated into the bones.

It is easy to dismiss the current trend for ditching cow’s milk as nothing more than a fad. Lactose intolerance is often misdiagnosed, and avoiding milk comes with risks of its own. Yet despite its ubiquity in the West, we are discovering that milk really is a most peculiar substance, and that as we live longer lives, it may have unexpected and potentially undesirable effects on the body. Rather than seeing it as a simple nutrient, we should perhaps come to revere milk as a complex signalling system, evolved to promote the optimal growth of infants. “Overall you have to balance benefits and risks and decide what is best for you,” says Givens. “There is clearly much more work needed on this.” In the meantime, the rest of us may want to question whether the pure milk moustache is a look we want to sport quite so often.

“As we live longer lives, milk may have undesirable effects on the body”

Want to know more? Read this in-depth look at the health claims of different milks.

This article appeared in print under the headline “Gone off”