In the many ongoing debates about healthy living and healthy eating, much attention has been paid recently to milk and other dairy products. Long considered a mainstay of healthy diets and particularly important for the growth and development of children, particularly in the Western countries, dairy foods and milk particularly have lately been questioned as to necessity, healthfulness and even safety. There are coherent arguments that can be made for and against regular consumption of dairy products. On balance, the current consensus is that, although there are some people who may be better off avoiding or limiting their intake of dairy, it is perfectly fine for most people to drink milk and eat dairy foods as they wish. The pros and the cons of dairy consumption are summarized below, focusing chiefly on milk as it is the origin of most dairy products and is for most families the most consumed dairy item.
Milk in children’s diets has been described as “one-stop shopping for nutrition”, with all of the basic nutrients needed for a child’s diet (fats, carbohydrates, proteins, vitamins and minerals except for iron). While all of these can be obtained from other sources, they are together in milk, which children will more easily and consistently consume than other sources, and which is in particular the most convenient source of calcium.
Among adults who drank milk, British studies of stroke and heart disease showed risk reduction in men with greater consumption of milk that appeared to be related to the milk intake. Lactose intolerance is a source of difficulty in milk consumption for adults and teenagers, and even for some children, but milk is readily available that is lactose-free or low in lactose, and in any case individuals vary greatly in their intolerance of lactose, and studies show that even the most intolerant can consume 1 to 1.5 cups, or 8 to 12 ounces, of whole milk without symptoms.
Milk is the most efficient dietary source of vitamin D as well as calcium, and a large randomized study in 2007 showed that boosting calcium and vitamin D levels significantly reduced the overall risk of developing cancer. Another major adult health concern, especially among women, is bone health, and osteoporosis, which may begin in childhood with low calcium consumption, has been called “a pediatric disease with geriatric consequences”; peak bone mass is reached during adolescence, and is facilitated by 4 to 5 servings a day of calcium-rich foods.
An increase in dietary calcium, most easily obtained from calcium-rich dairy foods, also moderates weight gain and reduces body fat content as compared to other foods of equal caloric content; the particular mixture of essential nutrients in dairy foods, especially calcium and protein, appears to speed up metabolism and accelerate the body’s ability to burn fat in general and the more harmful abdominal fat in particular.
Milk has sometimes been suspected of harmful effects on account of treatment of cows with synthetic bovine growth hormone made by recombinant DNA techniques, and of the addition of flavoring ingredients. The Food and Drug Administration several years ago found no difference between naturally-occurring bovine somatotropin (growth hormone) and that produced by recombinant or synthetic techniques, and no measurable differences in composition of milk from cows that receive recombinant growth hormone and those that do not. Children will generally consume milk readily, but this is sometimes facilitated by adding flavoring: the American Academy of Pediatrics has determined that, although the sugar content of unflavored milk is lower than flavored, the dietary contribution of any added sugar is “minimal”.
There is an increasing desire in most Western countries for “organic” food, although there is not universal agreement on what constitutes “organic” agriculture: the National Dairy Council, representing both organic and industrial dairy producers, has concluded that there is no identifiable difference between regular and organic milk with respect to 9 essential nutrients, and no difference in purity or safety between properly-produced organic and non-organic milk. Some nutritional advocates have argued that the mandatory pasteurization of milk has robbed it of useful components present in “raw” milk, but the universal consensus of nutritional and public health agencies in the United States and most of Europe is that the potentially harmful bacterial constituents of “raw” milk have been well demonstrated while the health advantages of unpasteurized dairy products have not.
Critics of milk consumption, especially by children, have often cited Dr. Benjamin Spock, who late in life wrote that “there was a time when it was considered very desirable, but research has forced us to rethink this recommendation…dairy products contribute to a surprising number of health problems:. Although dairy foods are prominent in the food pyramid put forward by the U.S. government, there is another pyramid, advocated by the Harvard School of Public Health, in which milk has little part and in fact figures as a source of risk, in the form of a relatively high calorie content (128 calories per cup of 2 per cent milk, for example) and a higher rate of fatal prostate cancer and slightly greater incidence of ovarian cancer among adults who drink milk. Dr. Spock also suggested that milk has little iron but may interfere with children’s ability to absorb iron and even cause subtle blood loss from the digestive tract in small children, thereby increasing the risk of iron deficiency anemia.
There have also been studies correlating the rate of milk drinking among adults with death rates in late life from coronary heart disease; in most European countries milk consumption went down during the 1990s and so did the rate of coronary heart disease, while the death rate from heart disease went up in Portugal, the one country in which the rate of milk consumption increased. Lactose intolerance can eliminate the nutritional benefits of milk, in that the calories, calcium and protein are lost and sometimes other nutrients as well in the diarrhea that attends milk consumption. Several recent studies of recurrent abdominal pain in children found that the symptoms were largely ascribable to lactose intolerance, and resolved with limitation or elimination of dairy intake. Some studies have also shown that milk intake may be associated with increased cancer risk, and this has been ascribed to an insulin-like growth factor (IGF-1), which is responsible for the beneficial effects of milk on growth in infants but which at higher levels and later in life promote the growth of cancer cells.
Some experts in bone health have questioned the value of calcium supplementation in childhood and adolescence for maintenance of bone health in adulthood. Some long-term followup of teenagers has suggested that their bone health in adulthood is more affected by their levels of physical activity in adolescence than by their milk consumption or calcium intake, and increases in milk consumption in later life have generally not been found helpful for bone health. Milk critics have also suggested that the amount of milk consumption advocated for weight loss was unusually high, up to 24 ounces over 24 hours, while more normal levels of milk consumption did not necessarily facilitate fat burning or weight loss.
With respect to the safety of treating cows with synthetic growth hormone, the food safety bodies of the United Nations, the European Union and several other industrialized nations have not reached a consensus that recombinant or synthetic bovine growth hormone is safe, and some of these have prevented its administration to dairy cows; the objections are based primarily on the cancer concerns regarding IGF-1, which is identical in cows and humans. Most of the flavorings added to children’s milk in the interest of palatability contain lactose, which raises again the concern about intolerance, and some of the flavored milk products may contain ounce for ounce as much sugar as soda pop.
Some dairy scientists have reported that cows raised by “organic” means, who eat fresh grass, clover and silage made from grass cover, produce milk that has 50 per cent more vitamin E, is 75 per cent higher in beta-carotene that is converted into vitamin A, contains 2 to 3 times the amounts of the antioxidants lutein and zeaxanthin and provide significantly more essential fatty acids than regular milk. Enthusiasts of unpasteurized milk also argue that raw milk has gotten a raw deal, and that its risk of bacterial contamination is low while beneficial bacterial species such as Lactobacillus acidophilus are more numerous in raw milk. Finally, some students of culture and animal behavior have suggested that drinking milk and eating dairy products is not “natural”, because humans are the only species that consume the milk of another species.
Balancing the pros and cons
The last argument is perhaps the most easily dealt with. We are perhaps the only species that drinks the milk of other species, but we are also the only species that builds computers, drives cars or does nutritional research. The evidence of the benefits of pasteurization is more substantial than evidence concerning the nutritional benefits of raw milk, and the reports that “organic” dairy products are more nutritious than non-organic ones is if anything an argument in favor of consuming dairy. The main problems posed by flavored milk involve sugar content and lactose intolerance, and people sensitive to sugar or intolerant of lactose might well avoid flavored milk.
The evidence that dairy products whose production involves giving cow synthetic growth hormone are safe can be debated, but there is more of it than evidence of health risks from hormones and other additives. It is not clear that milk or dairy products are helpful for losing weight or burning fat, but moderate daily consumption is unlikely to cause significant weight gain. Although physical activity is a significant contributor to adult bone health, an adequate intake of calcium and vitamin D is particularly important as well, and this needs to be obtained before adulthood; dairy products can be efficient and palatable sources of both. Foods rich in vitamin D and calcium may also decrease cancer risk; although some constitutents of milk such as the insulin-like growth factors might also promote the growth of cancers, this has not been proven.
People with lactose intolerance may have more trouble with dairy products than others, but most people deficient in the enzyme lactase can nevertheless tolerate moderate amounts of lactose, and lactose-free dairy products and dietary supplements to help with the symptoms of lactose intolerance are available. There are studies showing that milk consumption increases the risk of stroke and heart disease, and there are studies showing that dairy products may contribute to lower risk of these; the studies suggesting a benefit from dairy in the diet are more numerous, and in any case a correlation does not prove a cause. The number of doctors, nutritionists and institutions that recommend some dairy in the diet is greater than the number of those who appropriately worry about consuming too much; almost no one in this controversy has recommended doing without milk and dairy products entirely. The bottom line at present, therefore, is that dairy products are safe and healthy when like everything else they ate consumed in moderation.
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