Haydn Shaughnessy wonders just how many of the effects attributed to milk are really what they seem.
Milk, succour for babies and infants, and perfect for a cuppa, has no business being the centre of controversy but in the United States it certainly is. In some quarters of Ireland there are people with a keen eye on their wellbeing who go to the local health food store to seek out non-dairy alternatives, opting even for the unknown (soy milk, rice milk, oat milk) rather than drink Daisy's best.
And there are people who claim that the dairy version is responsible for skin ailments, gastric problems and worse.
The debate doesn't so much rage as simmer, forever on the backburner, getting no closer to resolution. Breastcancer.org, an online bible to many women who have suffered from a breast tumour or fear the possibility, singles dairy products out as one of the most significant tumour promoters.
Milk has also been implicated in cardiovascular problems because of its fat content. On the other hand, milk has become an ideal delivery mechanism for a variety of vitamins, minerals and now Omega oils, all carried as supplements in different brands of dairy sitting on the supermarket shelves slightly apart from their more mundane, homogenised and pasteurised cousins.
The National Dairy Council (NDC) of Ireland points out that as milk consumption has declined, many illnesses, not least those associated with obesity, have become more prevalent.
"Women who drink whole milk regularly," says Dr Leán O'Flaherty, nutrition manager at the NDC, "show no difference in weight from women who drink very little."
The NDC is promoting the Dash diet (Dietary Approaches to Stop Hypertension) - a diet rich in dairy as well as fruit and vegetables, on the back of evidence from the US that three servings of dairy produce a day can reduce hypertension and the risk of stroke.
"Research at Cardiff University in Wales," adds O'Flaherty, referring to a multi-country survey by epidemiologist Prof Peter Elwood, "has shown that milk consumption is associated with a modest decrease in cardiovascular problems."
Given that 98 per cent of Irish adults consume milk, 75 per cent eat cheese and almost 50 per cent use butter, getting the science of milk right assumes perhaps more significance than any other food and health issue we face.
Robert Cohen is a bullish American commentator who has taken the dairy industry to task in his book, Milk: The Deadly Poison, and on a website, www.notmilk.com, where he collates anti-milk research. It is a significant resource for opponents of the dairy industry.
Cohen lists on his website numerous studies that show dairy products cause cancer, osteoporosis, asthma, attention deficit disorder and other diseases. Osteoporosis is perhaps his most surprising claim, given that there is a general assumption that calcium from milk protects against it. The claim is lost though in the site's staggering range of anti-milk evidence.
One of those, the cancer connection, has gained some credibility with the publication of books such as Jane Plant's Your Life in Your Hands. In it, Plant tells of her aggressive, advanced tumour going into total remission once she gave up all dairy produce. There are other anecdotal anti-dairy stories on cancer-related websites such as www.breastcancercare.org.uk.
Milk's role in breast cancer is attributed to the presence of Insulin-Like Growth Factor-1 (ILG-1) in milk. ILG-1 production is stimulated by our natural growth hormones and it induces cellular growth and division, and the presumed risk is that cell division can get out of hand in the presence of excessive IGF-1. Bovine somatotropin, a growth hormone injected into cows in the US is, argue critics, likely to increase IGF-1 in milk.
Milk has also been blamed for a new generation of food intolerances. Liz Lipski, author of the book Digestive Wellness, says lactose intolerance (lactose is the protein in milk) is now a common problem and it can lead to numerous health problems that are remote from the stomach (for example, psoriasis) but which are caused by our inability to digest lactose. Lipski points out that, in contrast, fermented milk products like yoghurt and cheese do not seem to cause or provoke food intolerances.
She also believes the homogenisation process is partly responsible because it creates an enzyme, xanthiane oxydase, which irritates and damages the lining of the stomach.
Where does the truth of these claims lie?
Robert Cohen is incisive and humorous, but not particularly willing to indulge what he might regard as naive questions. To claims that milk can be made more tolerable through fermentation into yoghurt and cheese, he responds by calling them "absurdities". Osteoporosis, though he doesn't say it, can be caused by the general depletion of minerals that accompanies an acidic diet, typical of all western societies. Therefore, though milk consumption can be high, osteoporosis can still, sadly, happen.
Jane Plant's contention that milk-borne IGF-1 is responsible for breast tumour growth has a rational scientific logic. But there are three objections that haven't been given much of an airing.
The first is that testimony from breast cancer survivors has an inbuilt bias. Those sufferers who did quit all dairy and then went on to die are not around to write about it, nor to populate internet chat rooms and forums.
Secondly, IGF-1 appears to have a protective effect against diabetes because of its close relationship to insulin. The body's use of IGF-1, the balance of IGF-1 and other elements of body chemistry and diet are proving too complex for an easy call, right now.
Third, IGF-1 doesn't seem to trigger cancers.
The possibility that milk can provoke digestive intolerances, however, is now widely accepted but with reservations. Lactose intolerance, says O'Flaherty, is a problem faced by some infants. "Parents have the habit of putting their children on very restrictive diets not realising that the lactose intolerance passes with age. They outgrow it in most cases but remain on unnecessarily restrictive diets." O'Flaherty adds: "Many people claim they have a lactose intolerance. One in five people will make that claim but in reality the figures are much lower."
Like Liz Lipski, she points out that even people with lactose intolerance can usually tolerate yoghurt and cheese, but she rejects the idea that homogenisation causes problems with fat digestion or with a rogue enzyme, cautioning that "the body is, in fact, extremely efficient at absorbing fat, regardless of whether milk is homogenised or not".
The National Institutes of Health in the US, which serves a population made up of very diverse ethnic backgrounds, points out that lactose intolerance is the norm in humans. Only those from northern Europe or their descendants - as well as some dairy-herding peoples from Africa and Asia - do not have a susceptibility to it.
It may well be then that many of the effects attributed to milk are really less general than they seem. They may be applicable to some populations in different parts of the world and not to others. But not only ethnic complications are at work. Lactose intolerance is generally a problem for the young, while calcium depletion is a problem of age and of protein-rich diets.
Very few of us know how to adapt those diets to the unique needs of each stage of our lives. Nor do we necessarily read the health pages with a grasp of to whom a particular study might apply. Taking these two precautions might bring closure to the debate on milk's real effects, on whom and at what age. In the meantime, I vow to remain partial to a ripe French cheese.