Humankind has been consuming cows' milk as nourishment for thousands of years. Such use has contributed significantly to the development of civilization. Yet outcries to the effect that cows' milk as food is unhealthful, even poisonous, to humans have occasionally been getting play in the American media. The roots of this incongruity are complex. They lie in the culture of abundance that characterizes the present-day United States. Much of the negativism toward milk relates far less to health concerns than to antagonism toward animal agriculture. Getting the public to believe that milk consumption is deleterious to humans can make commercial dairy farming disappear, and such a disappearance would gladden animal rights activists and some environmentalists.
In the Beginning
If ever there were a natural food perfected by very long-term natural selection for mammalian health and survival, it is milk. According to the fossil record, mammals by definition a genus whose females secrete milk as food for their young offspring originated about 150 million years ago. Virtually all mammalian individuals producing deficient or unwholesome milk would have had no reproducing offspring and thus would have been barred from the gene pool.
Archeological evidence from the Middle East suggests that humans have been milking livestock for at least 8-10 millennia. The American dairy industry has grown concurrently with the U.S. On average among Americans, in the more than two centuries of this country's existence, health has improved and longevity and stature have increased. The calcium content of milk necessarily figured in the stature increase, because milk was the main dietary source of physiologically available calcium. More to the point is that, while millions of humans have consumed milk and milk products regularly and in significant quantities throughout several hundred years, there is no sound evidence that milk, or any milk component as such, has ever caused any widespread, serious human disease. If milk were, as the title of a 1998 trade book describes it, "the deadly poison" or even if its consumption were merely antithetical to good health, as many animal rights fanatics and health food fanciers claim the American dairy industry, which has flourished for decades, would have long ago gone bankrupt.
. . . [I]t appears that the [anti-dairy] coalition has targeted milk for the purpose of eliminating its ultimate target: animal agriculture.
Nutritional Utility, Safety, and Quality
In the U.S., public approval of cows' milk climaxed early in the 20th century, when it became widely known as "nature's most nearly perfect food." In that century, nutrition research established that cows' milk had more of the dietary essentials micronutrients, essential amino acids, and essential fatty acids in significant quantities than had any other single food. To my knowledge, no one has ever even attempted to refute that conclusion scientifically. Moreover, cows' milk provides protein of high quality, and nearly 77 percent of the calcium in the American food supply comes from milk and milk products. But as well as being a major source of the classical nutrients, cows' milk contains other bioactive substances enzymes, growth factors, hormones, and cytokines (hormonelike molecules). These four components of cows' milk may well prove significantly beneficial to human health.
Milk and milk products represent an outstanding achievement of American enterprise. The sanitation procedures the American dairy industry developed early on guided the processing of many other foods. American milk is clean, of uniform high quality, very palatable, and very widely available. Then, of course, there is the renowned culinary versatility of milk and milk products.
Down on Milk
As a whole, the anti-dairy coalition does not seem genuinely concerned about milk itself. Rather, it appears that the coalition has targeted milk for the purpose of eliminating its ultimate target: animal agriculture. The anti-dairy coalition has won wide approval even among persons who do not approve this goal. Its sympathizers and activist members include reporters, doctors, and dietitians. Thus, objective evidence of the healthfulness of milk consumption is becoming hard to come by.
Rejection of milk is commonly conveyed by remarks to the effect of "It's for kids." The implicit meaning of such remarks is that milk consumption is worthwhile during childhood and youth but not during adulthood. The assumption behind this implication is that the organs and tissues of adults have finished developing and that drinking milk, which conduces to growing up, is therefore absolutely superfluous for grownups. This assumption is not accurate. According to the best up-to-date evidence, the calcium in one's bones increases at least until the first half of one's third decade of life. Moreover, human cells of many types, including brain cells, replicate continually throughout adulthood. And among senior citizens, trying to maintain one's body is a challenge, as bones are thinning and muscles and other organs are weakening. Many seniors can benefit from consuming foods with proven utility for tissue maintenance, such as cows' milk.
Among other put-downs of cows' milk are statements that "it's for calves" and that human consumption of it is "unnatural." The substances in cows' milk that are essential nutrients for calves are also essential nutrients for humans. (Some of these essential nutrients were identified as such through research on farm animals.) And one cannot, considering the greatness of the range of what humankind ingests as food, reasonably describe human ingestion of bovine milk as unnatural. Indeed, more than any other plant or animal matter that humans consume, milk is human food by natural design. It is because of natural selection that the native peoples of Europe can digest lactose a disaccharide that is the principal sugar in human and bovine milk and a natural constituent only of milk.
. . . [M]ore than any other plant or animal matter that humans consume, milk is human food by natural design.
Epidemiologic Studies and Milk
Although on the whole epidemiologic studies yield very useful information, they can be a mixed blessing. They mainly generate data about associations (correlations), which are not necessarily causal, and they seldom establish cause-and-effect-relationships. Thus, epidemiological studies can make factors conditions, states, and actions that tend to coexist with particular ailments easy targets of junk science. Such a factor, however, is not necessarily the absolute cause of any ailment with which it has been associated statistically. Its association with a particular disorder may be purely a function of sample selection or of a statistical association with other coexistent factors. Or the factor in question may be a joint or secondary cause, or just an aggravator, of the disorder.
Often, shortly after a scientific study has generated findings of an association between a disease and anything else under investigation, researchers attempt to duplicate the study and/or to verify its findings. Quite often, such follow-up studies yield findings that are considerably different from, or even contrary to, the findings of the earlier study. Such a turn of events might well not deter disreputable and/or intellectually lazy persons and organizations from citing the earlier findings deceptively. Examples of findings from recent epidemiological studies that have made dubious the cumulative putative wisdom from many earlier studies include: (a) that following a low-fat, high-fiber diet is unlikely to reduce one's risk of developing colon cancer; (b) that hormone replacement therapy does not reduce the risk of having a heart attack; (c) that dietary fat is not a factor in the incidence of breast cancer; and (d) that ample consumption of fruits and vegetables does not contribute to preventing breast cancer.
In the Nurses' Health Study, of Harvard University, researchers found that the incidence of bone breakage (mainly hip fractures) among nurses who substantially drank milk surpassed that among their statistical counterparts who drank little or no milk. This finding certainly bears investigating. It has been established that intake of calcium (e.g., in the form that occurs in milk and milk products) is necessary for the development and maintenance of bones, and that it is important to bone strength and to preventing osteoporosis. Genetic, hormonal, motional, and/or nondietary behavioral differences may have accounted for the difference in the incidence of bone fractures between those nurses who drank milk substantially and those who did not so. There was also a relative lack of subjects who as teenagers had consumed more than three glasses of milk daily. The researchers found the lowest rate of hip fractures in the study among such subjects, but because of the relative fewness of these subjects, this finding was not statistically significant. Those subjects who as teenagers had consumed more than three glasses of milk daily were the only ones in the study likely to have had a daily calcium intake approximating that which the Food and Nutrition Board of the National Academy of Sciences terms "adequate" for persons 9 through 18 years old.
Regrettably, American girls during their teen years by the end of which period about half of their adult bone mass will have formed tend to refrain from drinking milk, apparently for fear that milk consumption will fatten them. But because milk (especially skim milk) has a relatively high volume-to-calories ratio, consuming it tends to satisfy quickly the desire to eat.
Recently, ample intakes of bioflavonoids pigments that are widespread in plants have become popular. Ingestion of bioflavonoids apparently contributes to preventing cancer and heart disease. But epidemiologic evidence suggests that there may be a correlation between ample ingestion of bioflavonoids and some forms of leukemia. Evidence from other studies suggests that isoflavones (e.g., from soy) may be an adverse factor in breast cancer. These findings alone, however, do not warrant recommending that all humans forgo consumption of plant foods of any kind.
Yet opponents of dairy have been doing something comparable to this, with battle cries such as "Milk causes cancer." Components of plant foods include varied allergens, toxins, and carcinogens but the concentrations of these components are such that, for most persons, they are not responsible for illness. Continually diversifying one's diet and avoiding overeating tend to prevent such illness.
No cause-and-effect relationship has been established between milk consumption and any major disease. No food, however, has been identified as perfect for the health of every human. Certain health factors genetic, allergic, or cardiovascular, for example make substantial consumption of cows' milk in its commonest American form (i.e., homogenized and pasteurized but otherwise un-processed) unhealthful or risky for some persons, such as those with certain cancers, heart disease, lactose intolerance, multiple sclerosis, or type 1 diabetes.
Stating publicly and flatly that "milk causes cancer" a commonplace among opponents of dairy is irresponsible. The major types of cancer include two that the anti-dairy coalition has singled out as alleged results of milk consumption: breast cancer and prostate cancer. Breast cancer is the commonest form of cancer among American women, while prostate cancer is the second commonest form of cancer among American men.
How breast cancer originates is unknown. Opponents of dairy at least imply, on the basis of statistics from cross-cultural studies, that it is be-cause women in China drink little or no milk that breast cancer is less prevalent among them than among women in the U.S. But cultural and genetic differences could well account for this discrepancy. In a study conducted in Finland, re-searchers found that among Finnish women the incidence of breast cancer was inversely proportional to milk intake.
Although an association exists between milk consumption and prostate cancer, the average age at which prostate cancer is diagnosed is 73 years, and it is rarely diagnosed in persons who have not entered middle age. Virtually every man at least 80 years old has prostate cancer, and most men of such age who have prostate cancer don't die of it. Thus, the association between milk consumption and prostate cancer is reasonably viewable as evidence that milk consumption contributes to longevity.
Evidence from feeding trials suggests that while milk consumption might activate prostate cancer, so might ingestion of calcium supplements. It would not be unreasonable for physicians to prescribe, according to results from prostate-specific antigen (PSA) tests, restrictions on calcium intake to those of their patients who have prostate cancer. Moreover, a means of reducing the calcium concentration of milk has existed for more than 50 years.
Aflatoxin, which can cause liver cancer, is produced by certain molds that contaminate stored foods. There is evidence, both from studies of humans and from experiments on laboratory rats, that milk consumption after exposure to aflatoxin promotes liver cancer. There is no sound evidence, however, that milk consumption sets off cancer of any sort. Indeed, it is well known that in ordinary circumstances laboratory rats on a diet of cows' milk and wheat (which is the standard diet for such animals) are without tumors throughout their lives.
Cow's milk contains substances that, at least hypothetically, are anticarcinogens. These substances in-clude butyric acid, carotene, conjugated linoleic acid (CLA), ether lipids, sphingomyelin, vitamins A and D, and whey proteins. Recent findings suggest an inverse relationship between CLA intake [See "CLA: Does Fat Have a Silver Lining?", Priorities, Vol. 8, No. 4, 1996, p. 44] and breast-cancer incidence. Ac- cording to the National Academy of Sciences, CLA is the only fatty acid that has unequivocally proved inhibitive of carcinogenesis in experimental animals.
Cholesterol, saturated fat, and heart disease
No epidemiological wave has affected as many persons as has that concerning dietary lipids and heart disease. Although elevated blood cholesterol is established as a positive risk factor for heart disease, there are many inconsistencies in the evidential picture of cholesterol and heart disease, and it is only in 15-20 percent of humankind that cholesterol intake significantly affects blood concentrations of cholesterol. Cholesterol constitutes only 0.30-0.35 percent of milk fat (butterfat), and consuming skim milk tends to reduce blood concentrations of cholesterol. According to a current theory, oxidized cholesterol which occurs both in foods and as a human metabolic byproduct can inflame blood vessels and thus increase one's risk of having a heart attack.
Another positive risk factor for heart disease is saturated fat intake. It seems, however, that the crux of this risk factor is the intake of myristic acid and palmitic acid. Both of these fatty acids are constituents of milk fat. This is what chiefly connects heart disease and milk and milk products. Palmitic acid and, particularly, myristic acid apparently promote incorporation of cholesterol into low-density lipoprotein (LDL) a lipid-protein complex that is a major carrier of cholesterol in the bloodstream. An association exists between elevated blood concentrations of LDL and an increase in the risk of developing coronary heart disease (CHD).
But there is experimental evidence that feeding CLA, which occurs mainly in milk fat, to laboratory animals can prevent in them formation of the plaques that characterize CHD. Another form of CLA has proved inhibitive of fat storage in experimental animals.
An autoimmune disease is any of a group of diseases characterized by the production of antibodies against cells that are normal and belong to the body. Examples include multiple sclerosis (MS), rheumatoid arthritis, systemic lupus erythematosus, and type 1 diabetes. Pathologists hold that such diseases involve genetics, viruses, and other environmental factors. They may involve food proteins. For example, butyrophilin a protein in the membrane of fat globules in milk gives rise to an antibody that cross-reacts with a protein in the myelin sheath (an insulator on some neurons). And another milk constituent bovine serum albumin (BSA) can induce production of an antibody that cross-reacts with a protein on the surface of beta cells (pancreatic cells that make insulin). The resultant binding induces immune-system attacks on tissues it characterizes. There is an epidemiological association between milk consumption and MS (which is marked by destruction of myelin) and between milk consumption and type 1 diabetes (which stems from the immune system's destruction of beta cells).
It appears, however, that in some circumstances butyrophilin and BSA might be helpful in restraining MS and type 1 diabetes, respectively. And no doubt certain nondairy food proteins are also factors in autoimmunity. It be-hooves the health-science research community to seek (a) to define the relative significance of milk intake in autoimmune diseases and (b) to formulate a means of detecting susceptibility to autoimmune food proteins. In any case, milk can be made free, or nearly free, of butyrophilin and/or BSA, and consuming skim milk in place of whole milk can considerably reduce one's exposure to butyrophilin.
The American Academy of Pediatrics recommends that children be breast-fed regularly until they are 12 months old, to foster the infant's gut and immune system. During the first year of life, the human gut is more permeable than it normally is at any other time of life, and peptide fragments and even intact food proteins can enter the circulatory system intestinally and trigger antibody production.
The natural ability to digest lactose depends on a gene whose expression is virtually universal among human infants and is widespread among children and adults of northern European extraction. The gene is largely unexpressed, except in infancy, among Native Americans and Orientals and in some African populations. Lactose left undigested in the intestine can ferment, and such fermentation can cause abdominal pain, bloating, and diarrhea.
Most Americans do not get lactose-related indigestion, and since the gene for lifetime lactose digestion is dominant, it is spreading in the U.S. population. Being African-American, for example, does not entail lactose intolerance. In any event, lactose intolerance can be managed easily. Both lactase-treated milk and lactase pellets (designed for addition to liquid milk products) are on the market. Lactase-treated milk is slightly sweeter than, but is otherwise identical to, milk that has not been thus treated. And culturing milks with microorganisms that break down lactose makes them more di-gestible to persons with lactose intolerance. Such products include buttermilk and yogurt. Cheeses contain little or no lactose, and butter lacks it completely.
The Bottom Line
Knowledge from nutritional biochemistry and experience over centuries have established that cows' milk is excellent food for humans. It is, for example, a superior source of calcium and high-quality protein. Including milk in one's diet is good nutrition insurance and is absolutely consistent with the sound recommendation of keeping one's diet diversified. More-over, cows' milk is culinarily versatile and is adaptable to many human conditions.
ACSH scientific advisor Stuart Patton, Ph.D., is Professor Emeritus of Food Science of The Pennsylvania State University.
(From Priorities, Vol. 13, No. 2)