WORRYING ABOUT milk
T. COLIN CAMPBELL GREW UP ON A small dairy farm of 210 acres, nestled among glorious green pastures near the Shenandoah Valley in northern Virginia. Almost from the moment he learned to walk, he dogged the footsteps of his father, Tom Campbell, as he tended the farm’s 20 to 30 milk cows. Eventually, young Colin was given the chore of “stripping” by hand any milk from the cows’ udders that the milking machine left behind. He also learned how to operate the family butter churn and, on special weekends, helped man the hand-crank bucket used to make ice cream. The Campbells were a simple family, without much money, but considered themselves blessed to have milk straight from the cow. “We had the nectar of life,” Campbell says. “I was proud of the fact that somehow, every day, I could drink a gallon of milk, or more.” [paragraph] Campbell went on to devote his life to nutritional research. Two decades ago he contributed to the first federally funded report on the relationship of diet to cancer, an influential study that helped establish the nutritional importance of grains, fruits, and vegetables. At age 66, he is nearing retirement as a nutritional biochemist at Cornell University. He is also president and CEO of Paracelsian, a company that promotes holistic health and sells assays to measure dioxinlike chemicals and evaluate herbal products. Campbell lives on a quiet residential street near the Cornell campus, by all appearances like most of his neighbors. But these days not one drop of milk touches the lips of anyone in his household, and his refrigerator is stocked with soy cheeses, sorbet, and rice milk. “People might think we’re nuts,” he says. “But nondairy beverages and foods are pretty good once you adjust to the the taste.”
Like most Americans, Campbell once assumed that dairy products were not only wholesome but also an essential part of the daily diet for anyone desiring good teeth and strong bones. After years of scientific research, however, he’s now convinced that cow’s milk is responsible for a share of our nation’s medical woes. The fact that fats in dairy products can contribute to hardening of the arteries and heart disease has long been common knowledge. But Campbell worries that stocking up on skim milk and low-fat yogurt–or going organic because of concerns about cows exposed to pesticides, antibiotics, and bovine growth hormones–may offer only limited protection against the potential health hazards of milk. Unlike most nutritionists, he questions even the much-touted health benefits of milk. And he believes his research raises issues his colleagues have tended to ignore.
The bottom line for Campbell is simple: “It’s unnatural to drink milk.” Most adults in Asia and Africa, along with many in southern Europe and Latin America, have trouble digesting lactose, the main sugar in the milk of both humans and cows. Some suffer from bloating, cramps, or diarrhea if they try. A 1978 population survey, compiled by geographer Frederick J. Simoons of the University of California at Davis, suggests that it was only because of a genetic aberration that milk became a food staple in northern Europe and North America. Nature normally programs the young for weaning before they reach adulthood by turning down production in early childhood of the enzyme that breaks down lactose. But a gene mutation inherited by people of northern European descent prevents the production of this enzyme from being turned down. As a result, the majority of Americans can drink milk all their lives.
Campbell argues that the ultimate problem with cow’s milk is that nature concocts different formulas of mother’s milk for different species. What’s good for baby calves isn’t necessarily good for human babies or adults. “Isn’t it strange that we’re the only species that suckles from another species?” he says. Campbell theorizes that cow’s milk unnaturally stimulates enzymes and growth hormones in the human body that increase the risk of various diseases. Moreover, he has come to the conclusion that cow’s milk may not even do what it is supposed to do best–build strong bones. And recent studies suggest that humans may need less calcium for strong bones than was once believed and that other foods, including various vegetables and legumes, may be better sources than cow’s milk.
“It would be hard to imagine a worse vehicle for delivering calcium to the human body,” says Neal Barnard, head of the Washington, D.C.-based Physicians Committee for Responsible Medicine, a nonprofit advocacy organization that promotes vegetarianism and is opposed to milk consumption. Of the 100,000 or so members of the Physicians Committee, about 5,000 are actually physicians. Both Barnard and Campbell, a science adviser for the group, believe that government officials have turned a blind eye to the potential health risks of milk. Last December, the Physicians Committee filed a lawsuit against the U.S. Departments of Agriculture and Health and Human Services claiming the agencies unfairly promote industry special interests through official dietary guidelines. The USDA, the Physicians Committee argues, has an inherent conflict of interest: a dual mission to assist dairy farmers as well as to promote good nutrition. What if the subsidized dairy foods that the government recommends aren’t good choices for healthy eating?
Government health officials argue that evidence of health risks from milk is circumstantial. Moreover, they contend that dietary guidelines that focus on dairy products as a major source of calcium are based on a realistic assessment of the food choices most Americans make. “There’s nothing against vegetable sources of calcium,” says Eileen Kennedy, deputy undersecretary of research; education, and economics at the Department of Agriculture. “But we have to fashion healthful eating around current habits.”
In Campbell’s view, such thinking is circular. The reason a lot of Americans follow a dairy-rich diet, he argues, is that they assume it’s the healthy thing to do.
Gregory Miller, vice president of nutrition research at the National Dairy Council, dismisses the Physicians Committee as “essentially an animal rights organization. If consumers want nutritional advice” he says, “they should get it from mainstream health and medical health professional organizations…. Here they are saying don’t eat the food group that provides 75 percent of calcium in the diet. With little kids who don’t like vegetable sources like broccoli and kale and brussels sprouts, it becomes especially important.”
Campbell, who believes all animal protein is bad for human health, says he is not an animal rights activist. He believes that animal experimentation is essential for research.
ALL THROUGH HIS UNDERGRADUATE YEARS AT PENN STATE and then veterinary school at the University of Georgia, Campbell spent his time happily milking the family cows during summer vacations and drinking glass after glass of fresh whole milk. When he transferred to Cornell in 1956, after landing a full scholarship for doctoral studies in animal nutrition, he set out to learn how to produce more animal protein “so we could eat more of it.” But his outlook changed after he headed overseas in 1965 to serve for 10 years as coordinator of a U.S. AID project in the Philippines, where poverty-stricken children were dying mysteriously from liver cancer believed to be linked to malnutrition. For protein, the children depended largely on peanuts, which in the tropics often contain relatively high amounts of aflatoxin, a carcinogen produced by mold growth. To his surprise, Campbell discovered during his tenure in the Philippines that the incidence of liver cancer was especially high among some of the best nourished kids, whose diets were supplemented with powdered milk provided through a U.S.-subsidized program. He was completely baffled until he read about a 1968 research study conducted in India by Madhavan and Gopalan and published in the Archives of Pathology. The study linked a milk protein to liver cancer in lab rats. “That was a signal event for me,” Campbell says.
Left with the suspicion that feeding milk to the Filipino children may have been a mistake, Campbell began studies to explore the question. During the next three decades, he conducted a series of lab experiments at Cornell and Virginia Tech and found that rats given a brief initial exposure to aflatoxin tended to develop liver cancer when fed casein, the main protein in milk. “We could turn on or turn off cancer growth,” he says, by increasing or decreasing the amount of casein.
Are such animal studies relevant to humans? One common theory on cancer development, first advanced in 1939 by Berenbloom and Shubik, is that tiny precancerous lesions accumulate throughout the body because of random mutations or exposure to small amounts of carcinogens. These lesions normally remain dormant, but a steady dose of cancer promoters in the diet may override natural defenses against the growth of tumors. In laboratory experiments on animals, scientists try to re-create this two-stage process. Aflatoxin, in Campbell’s experimental model, stands in for any kind of carcinogen to which a human might be exposed. In lab animals, the liver has become a litmus test for cancer studies because of its sensitivity to carcinogens and its rapid reproduction of cells. And among lab animals, rats are considered particularly relevant to human cancer studies because they need the same nutrients and proportion of protein for maximal growth as humans. But lab rats often don’t get cancer from suspected food carcinogens unless they are given enormous doses. Since humans normally receive far less exposure, it’s not clear if the tests always reveal a significant danger. Campbell chose to feed casein to rats in normal doses, with 15 to 20 percent of their diet (by weight) coming from casein. The typical American diet is roughly 17 percent protein, says Campbell, though the protein, of course, is not all casein. He found that the threshold amount of casein required for switching on tumor growth averaged around 10 percent of the diet.
E. J. Hawrylewicz, a nutritional biochemist and research director at Mercy Hospital and Medical Center in Chicago, performed a somewhat similar series of experiments that revealed lab rats are more likely to develop breast cancer tumors when fed casein than when fed soy protein. But he found that the lab rats’ diets had to be rich in casein, at least 20 percent, to produce significantly more tumor growth, as opposed to Campbell’s results of 10 percent. Because Americans consume a variety of proteins to reach 20 percent–mostly from animal foods like eggs and meat in addition to dairy–Hawrylewicz argues that casein may not be harmful if consumed in modest amounts: “I would definitely not say that it’s anything alarming.” Nonetheless, Hawrylewicz agrees with Campbell that a good anticancer strategy is to choose a diet rich in plant rather than animal proteins.
But Miller, of the Dairy Council, contends that casein is a red herring. He and other nutritionists cite evidence for the health benefits of dairy products: studies linking milk consumption to bone growth, reduced blood pressure, and reduced risk of colon cancer. And, he adds, “other milk proteins have demonstrated anti-carcinogenic properties.”
In cancer research, pinpointing a singular mechanism that triggers tumor growth is invariably an elusive quest. Each cell where cancer may develop passes through several precancerous stages; some may have mechanisms in common and yet have other pathways peculiar to one bodily organ–lymph nodes, say, or brain cells. “There are likely many, many mechanisms,” Campbell says. But epidemiological research adds a new line of evidence, and in this case it suggests a correlation between milk consumption and at least two kinds of cancer prevalent in Europe and North America: breast and prostate.
In Asia, where many people drink no milk whatsoever, breast cancer tends to be rare. In rural China, for example, among women aged 35 to 64, Campbell found that breast cancer deaths averaged 8.7 per 100,000, as opposed to 44 per 100,000 in the United States. In India, where people eat more dairy in the form of yogurt, other researchers have documented higher rates of breast cancer, but they are still lower than those of Western nations. The same pattern holds true, Campbell says, when you narrow the focus to the West alone. A comparative study published in 1989 showed that even in Europe, two areas with higher milk consumption–Scandinavia and the Netherlands–also had higher breast cancer rates.
Worldwide, men seem far more likely to die of prostate cancer in countries where dairy consumption is high than in countries where it is low. A study published in 1977 revealed that 10 men die of prostate cancer in Western Europe for every one who dies in Asia.
Such cross-cultural studies are provocative, but they are by no means definitive proof because they often contain hidden variables. More precise results come from careful single-country studies that track individuals and their food choices for several years. Recently, two large, lengthy studies in the United States linked dairy consumption to prostate cancer. In the Physicians’ Health Study, researchers tracked 20,885 male doctors over 10 years. Those who consumed at least 2 1/2 servings of dairy food per day were 30 percent more likely to develop prostate cancer than doctors who consumed less than half a serving. A 1999 study of nearly 50,000 subjects, called the Health Professionals Follow-Up Study, had found that men who consumed a lot of dairy products had a 70 percent higher risk of prostate cancer. If they also took calcium supplements, their risk jumped dramatically: Those who consumed a total of more than 2,000 milligrams of calcium per day raised their risk of metastatic prostate cancer more than fourfold. While these results hint at a link between milk and cancer, they are far from conclusive.
Still, Edward Giovannucci, an associate professor of nutrition and epidemiology at Harvard and a coauthor of both studies, sees reason for concern. He believes that calcium itself, at high levels of consumption, promotes prostate cancer by depleting protective levels of vitamin D. Many years of research, not just two studies, have convinced him. “For prostate” he says, “the data are generally consistent, and the high relative risk in the Health Professionals Study is quite worrisome,” given the push for high calcium intakes in the United States.
IN THE UNITED STATES, 10 MILLION MEN AND WOMEN SUFFER from osteoporosis, a chronic bone-wasting disease. One in two women and one in eight men over age 50 breaks a bone because of osteoporosis. After a hip fracture, many never recover their mobility, and one in five dies within a year.
Many experts argue that Americans of all ages can stave off the onset of osteoporosis by adding more calcium to their diets. Bess Dawson-Hughes, chief scientist of the Calcium and Bone Metabolism Laboratory at Tufts University and president-elect of the National Osteoporosis Foundation, says the vast majority of U.S. teenagers and adults–70 percent of men, 90 percent of women–don’t get enough calcium from their diets. “We’re talking about a major deficiency,” roughly half the recommended amount, she says. And milk has lots of calcium.
Some nutritionists, however, see the problem and the solution differently. Walter Willett, a professor at the Harvard School of Public Health and chairman of the nutrition department, says, “There is no evidence that we have a calcium emergency, as the dairy industry would have us believe. We have one of the highest calcium intakes in the world.” Marion Nestle, chair of the nutrition and food studies department at New York University and a member of the Food and Drug Administration’s science advisory board, was surprised when the Institute of Medicine recently suggested that teenagers and adults over 50 increase their calcium intake to 1,300 and 1,200 milligrams, respectively, a day. “I think it’s amazing to have set the calcium requirements so high,” she says. The World Health Organization recommends 500 milligrams for children and 800 milligrams for adults.
To support the U.S. recommendations, researchers like Dawson-Hughes cite a consistent body of evidence. Many dozens of controlled clinical studies show, without a doubt, that increasing calcium intake adds bone mass. Therefore, they insist, dairy foods can fight osteoporosis. Milk, after all, is a package of nutrients that nature concocted to foster rapid growth in calves. But a growth spurt may not ensure the lifelong strength of bones. “The studies of bone mineral density can be highly misleading,” says Willett. “What is clear is that an increase in calcium intake causes a onetime small increase in density (about 2 percent). However, this does not continue to accrue and disappears when stopping the extra calcium.” The question is whether sustaining this slight increase will protect against fractures.
Campbell stumbled across statistics about osteoporosis in the 1980s when he took a break from his animal studies to direct the China-Oxford-Cornell project, a massive investigation of diet and disease based on data gathered from 6,500 rural Chinese families. In general, the Chinese ate a nearly vegetarian diet. Another pronounced difference between China and the West caught Campbell by surprise: the contrasting levels of osteoporosis. Most Chinese were getting their calcium from vegetables and fruits alone. Although they got less than half the calcium recommended by the USDA, their bones seemed healthy. Among women over 50, the hip fracture rate appeared to be one fifth as high as in Western nations.
Were the Chinese absorbing calcium more efficiently from vegetables than Westerners were from dairy foods? Or might the rural Chinese, with their hard labor outdoors, make up for low amounts of calcium in their diet with exercise-induced bone growth? Campbell wondered if their milk-free, vegetarian diet could be part of the answer. Although milk’s calcium and other nutrients do promote bone growth, says Campbell, other substances in dairy foods and other animal products–certain proteins and especially sodium–actually leach some calcium from bone. The Chinese were evidently getting sufficient calcium from dark green vegetables, legumes, and some fruits. And because those foods don’t also promote calcium loss, the Chinese might not need to take in as much calcium overall. Campbell later learned that disparities between calcium intake and bone health can be seen worldwide. By the 1990s, nutrition researchers had gathered data from different parts of the world and found another surprising correlation: The more calcium people consumed, the more susceptible they seemed to be to hip fractures. People in those countries that consume the highest levels of dairy foods (North American and northern European nations) take in two or three times more calcium yet break two or three times more bones than people with the lowest calcium intake (Asians and Africans). “Osteoporosis,” Campbell notes, “is not yet fully explained.”
In 1997, results from a massive research project–the 12-year Harvard Nurses’ Health Study involving 78;000 nurses–added more epidemiological evidence. At the beginning of the study, nurses reported on dairy foods in their diets, then updated the information every few years. The updates included reporting arm and hip fractures. (Researchers felt that if they collected data the other way around, nurses who had broken bones might retrospectively blame their diets and not remember dairy consumption as accurately.) The analysis corrected for variables affecting bone strength, such as age, vitamin and mineral consumption, caffeine, smoking, alcohol consumption, hours per week of vigorous physical activity, and birth control and hormone supplements known to stimulate bone growth. At the conclusion of the study, Diane Feskanich, Walter Willett, and colleagues at Harvard noted a correlation: Nurses who drank the most milk–two or more glasses per day–broke more bones than the others. They had a slightly higher risk of arm fracture (1.05 times) and significantly higher risk of hip fracture (1.45 times).
Robert Heaney, a professor of medicine at Creighton University in Omaha and a specialist in bone biology, questions the value of this study and cites others that contradict its findings. Of 40 to 45 studies looking at controlled calcium intake and bone loss, he says “all but two showed a benefit from calcium. Eight to 10 of the studies used dairy products; every one showed bone benefit.” Even in some 80 studies that didn’t control calcium intake but simply relied on subjects’ reported intake, he says 75 to 80 percent were positive, showing less bone loss, fewer fractures, or more bone gain.
THANKS TO CONGRESS, DAIRY PRODUCERS ENJOY PRICE SUPPORTS and government purchase of surplus production. They plow some of their profits into promotional industry groups that fund research studies, they educate health professionals about milk, and they provide free materials to schools suggesting that milk is vital to good nutrition. In its lawsuit, the Physicians Committee for Responsible Medicine alleges that the federal dietary guidelines are prepared by advisers with ties to the meat and dairy industry. But Miller says, “The bottom line is that the current recommendations for dairy and calcium intake are based on available science. The people who formulated the recommendations are sound scientists who are at the top of their field, well respected. To suggest that they made those recommendations based on politics rather than science is just plain wrong.”
U.S. Department of Agriculture deputy undersecretary Eileen Kennedy notes that consumer preferences–not dairy promoters–shape federal nutrition policies. Americans get three fourths of their calcium from milk and other dairy products. Consider, Kennedy suggests, what would happen if the government removed dairy as a recommended food group. Would people fill the gap by eating more calcium-rich vegetables and legumes? Kennedy thinks not. They’d continue to follow current trends–shirking exercise that builds bone, consuming more foods such as caffeinated sodas, salted snacks, and meats that actually leach calcium from bones–and they’d be worse off than ever with less milk. “You can’t simply lop off the milk section and say the rest works,’ she says. And no one can deny that the consumption of milk per capita has been slowly dropping for decades. Americans now drink more soda than milk. They also drink more coffee than milk and more beer than milk.
In the National School Lunch Program, however, milk is the only beverage that must be offered to children. A section of the Physicians Committee lawsuit alleges that milk’s unique status in school lunches amounts to racial discrimination. Studies suggest that 70 percent of African-Americans, 50 percent of Hispanics, and 90 percent of Asians have trouble digesting lactose, while only 15 percent of Caucasians do. Lactose-intolerant children could get enough calcium by drinking alternatives such as soy milk or calcium-fortified juices, but, according to the lawsuit, the program that serves free meals to needy children won’t reimburse schools for a nondairy alternative to milk unless the substitution is requested by a doctor.
Dairy proponents insist that most people who think they are lactose intolerant can actually digest small amounts of milk–the trick is to train them. Indeed, pilot studies funded by the dairy industry have shown that when such children consume milk slowly, in sips throughout the day and with meals, they can often tolerate one or even two glasses daily. “What’s really, racist is telling them they can’t consume a food that’s nutritious, affordable, and convenient,” says Mille.
Meanwhile, Campbell cannot forget the children he set out to help in the Philippines long ago. He raised all five of his own children, ages 22 to 36, on nearly milk-free diets. And his five grandchildren seldom touch dairy foods.
Outside the family, Campbell faces more resistance to his diet ideas, but that hasn’t shaken his conviction that people can get all the calcium and protein they need from nondairy and plant sources. Antonia Demas, a former Cornell colleague of Campbell’s now working in the school system in Miami, Florida, has created award-winning school lunch programs that don’t include meat or dairy foods. But she admits that kids still like the diet they’re used to. And even Campbell admits his grandkids slip every now and then. “They’re almost strictly vegetarian,” he says, “except a couple who cheat a little on cheese once in a while.”
WHERE’S THE CALCIUM?
Milk is commonly thought to be the premier source of calcium, but many other foods contain calcium. Consider that a cup of cow’s milk contains about 300 milligrams of calcium. The following portions of foods each supply the indicated amounts of calcium: a cup of collard greens (148 mg], an ounce of Swiss cheese (262 mg), ten dried figs (269 mg), three ounces of sardines (372 mg). Even foods such as turnips and kidney beans contain some calcium. A 1988 study suggested that those who eat a plant-based diet may not need as much calcium as those who consume a diet rich in animal proteins. And official opinions on calcium needs vary. In the United States, the suggested daily calcium intake is 800 milligrams for kids 4 to 8, 1,300 milligrams for kids 9 to 18, and 1,000 milligrams for adults. In the United Kingdom, the recommended calcium intake for kids ranges from 350 milligrams to 1,000 milligrams a day, depending on the child’s age, while the recommended amount for adults is 700 milligrams.
While interviewing Colin Campbell, the biochemist and nutrition researcher at the center of this month’s story about milk (“The Trouble With Milk,” page 44), Hively found that his understanding of the scientist changed profoundly. “He seemed at first to be very agitated, with strong feelings about nutrition and diet,” says Hively. “But after a while I started sensing that he was just very committed to speaking the truth as he saw it. He seemed courageous to me. He doesn’t see anybody else willing to talk about what he has learned, so he figures he has to do it.” Hively has written for Discover for 11 years on topics from flywheels to feet. His latest book, The Eternal Darkness, coauthored with deep-ocean explorer Bob Ballard, was published in March by Princeton University Press.
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