While celebrities and U.S. officials endorse milk as a near-perfect food in slick “milk mustache” ads and elsewhere, emerging research is raising questions about milk’s wholesome reputation.
The studies, though far from definitive, suggest that consumption of cow’s milk may be associated in some people with a higher risk of diabetes, prostate cancer or ovarian cancer.
And the well-known Nurses’ Health Study reported two years ago that older women who drank two or more glasses of milk a day had no greater protection from hip or forearm fracture than women who drank one glass or less a week.
“High milk intake and better bones is not well-established,” said Dr. Meir Stampfer, professor of epidemiology and nutrition at the Harvard School of Public Health, and one of the researchers involved in the Nurses’ Health Study. “And I’m not convinced that the data are really strong enough to support the very vigorous type of pro-milk campaign” that is now being promoted.
But government officials, other health professionals and the dairy industry say there is plenty of data to support the health benefits of low-fat milk and other dairy products in preventing not only osteoporosis, but also high blood pressure and possibly colon cancer.
They say there is a “calcium crisis” in the U.S. now, with children and adolescents drinking more sugar-laden soda and less calcium-rich milk, putting them at risk of developing osteoporosis, the bone-thinning disease, and bone fracture in their later years. Milk is not only fortified with vitamin D to help the body absorb calcium, they say, it also provides riboflavin and other essential nutrients.
“The concern we have is that you’re going to have, in the very near future, a generation of people, especially women, who are developing significant osteoporosis and developing it younger than in the past,” said Dr. Jonelle C. Rowe, a physician on the staff of the National Institute of Child Health and Human Development, which currently has a “Milk Matters” public health campaign to encourage children and adolescents to increase their calcium intake.
While the scientists who are finding the unsettling though preliminary results on milk and health do not believe cow’s milk is necessarily harmful, they say there is an overemphasis on milk in the diet. There are other ways to get calcium, they say, pointing to calcium-fortified orange juice or leafy green vegetables.
And a little daily sun exposure year-round can allow the body to make all the vitamin D it needs to absorb calcium (or a vitamin D or multivitamin supplement for those in northern latitudes or for those who are housebound), while weight-bearing exercise helps build bone mass.
Much of the current controversy surrounding milk began because so many adults, particularly minorities, have difficulty drinking it because they gradually lose an enzyme to digest milk sugar, or lactose. About 90 percent of Asians, 70 percent of blacks and Native Americans, 50 percent of Hispanics, and 15 percent of whites have difficulty digesting lactose, according to a review of the literature by the Physicians Committee for Responsible Medicine, which is filing suit against the U.S. government for being racially biased in its dietary policy.
But milk supporters dispute the claim that people who have difficulty digesting lactose cannot safely or comfortably drink milk. They say even people with little or none of the enzyme needed to digest the sugar can gradually work their way up to a glass of milk a day. Or they can eat yogurt and cheese, in which lactose is broken down, or use products that have reduced lactose or an enzyme needed to digest lactose.
“Almost anyone can tolerate a glass of milk . . . or the lactose-equivalent of a glass of milk,” said Dr. Nevin S. Scrimshaw, a physician and MIT professor emeritus who taught at the Center for International Studies, and is currently president of the International Nutrition Foundation, a private Boston-based non-profit organization that works to fight hunger and improve nutrition around the world.
“If you drink a glass or two of milk a day, you’ve got the additional calcium, got the protein, got the riboflavin,” said Scrimshaw, who has served as food and nutrition adviser to a United Nations program, as well as conducted studies in black Americans and others who have difficulty digesting lactose and found they can gradually adapt to a glass of milk with little or no discomfort, particularly if they drink it during meals.
But when people do experience discomfort, it can be severe. Some people with lactose intolerance may experience abdominal bloating, cramps, flatulence, nausea and severe diarrhea by drinking even a single glass of milk. People who regularly experience severe diarrhea may not properly absorb nutrients, because they’re lost from the body so quickly.
The role of milk in the U.S. diet is currently being assessed as the government prepares to revise its dietary guidelines for the first time in five years. A government-appointed committee of doctors and nutritionists — including Harvard’s Stampfer and Tufts’ Johanna Dwyer and Alice Lichtenstein — was expected to give its dietary guidelines recommendation to the government by the end of the year and the final guidelines are expected in the spring.
Even scientists and health officials who recommend 2-3 servings a day of cow’s milk and other dairy products point out that it’s best for infants to be breast-fed in the first year of life. The American Academy of Pediatrics made the breast-feeding recommendation in the early 1990s, after research indicated that cow’s milk or cow’s milk-based formula could increase the risk of type 1 diabetes in some children, perhaps as a result of an autoimmune reaction to a protein in milk.
Type 1 diabetes, also called insulin-dependent diabetes, has long been known to have a genetic component, but the possible contribution of cow’s milk and other environmental factors is now being explored, particularly in Finland, where there are higher rates of both type 1 diabetes and milk consumption, said Jill Norris, an epidemiologist and associate professor at the University of Colorado Health Sciences Center, who has done some of the research.
But while cow’s milk should be kept from infants, it needs to become a bigger part of the diet for children and teenagers, according to U.S. health officials. USDA statistics indicate that adolescents are drinking twice as much soda — more than 12 ounces a day — and half as much milk — about 6 ounces a day — as they were 20 years ago. Early attempts by the soda industry to fortify beverages with calcium didn’t work, since the caffeine in cola counteracts the effectiveness of calcium. The orange juice industry has recently taken to fortifying its products with calcium with an amount equivalent to that found in skim milk: about 300 milligrams a cup.
The usual adult calcium recommendation is 1,000 milligrams, while women who are pregnant, nursing, or postmenopausal are urged to get 1,500 milligrams a day.
Researchers who view cow’s milk from an anthropological and evolutionary point of view say the product is not necessarily a dietary requirement for humans, especially adults.
Cow’s milk has been in the human diet less than 10,000 years, a drop in the evolutionary bucket, when dairy farming started in parts of northern Europe and what was once known as the Near East (and today called the Middle East). The first cows were brought to America less than 400 years ago, by Pilgrims who settled Plymouth Colony.
That’s why most adults who have the enzyme that digests lactose are descendants of people from those dairying cultures. As a result, Robert Dirks, professor of anthropology at Illinois State University and a specialist in food and culture, said he thinks of milk as an “ethnic food.”
And Frederick Simoons, a University of California, Davis, professor emeritus of geography, said it’s a “normal human condition” for people to have a decline in the enzyme that digests lactose as they reach adulthood.
But today, “Certainly a lot of prominent people feel quite comfortable that milk is a good thing; even Donna Shalala gets her milk mustache, doesn’t she?” said Dr. Daniel W. Cramer, professor of OB/GYN and reproductive biology at Brigham and Women’s Hospital and Harvard Medical School, referring to the U.S. Secretary of Health and Human Services’ appearance in the industry-sponsored “Got Milk?” ads featuring well-known people with milk mustaches.
“But not everybody signs off on this idea that there can’t be anything wrong with consuming milk as an adult,” Cramer said.
Cramer has researched a potential link between milk and ovarian cancer and infertility in a study involving 500 Massachusetts women and in international comparisons of health statistics based on a country’s milk consumption. While the possible mechanism is not known, Cramer hypothesizes that it involves galactose — a metabolic byproduct of milk sugar, or lactose — based on his and others’ findings that the rates of ovarian cancer and infertility appear to be elevated in women who are able to break lactose down into glucose and galactose, but are then unable to metabolize galactose further.
Among the other emerging research findings that raise questions about milk, but that still need to be confirmed by other studies: Men with high calcium consumption, whether from milk or elsewhere, are at 4.5 times the risk of getting metastatic prostate cancer.
Dr. Edward Giovannucci of Harvard Medical School and Harvard School of Public Health postulates that the link between prostate cancer and calcium he and his colleagues found in the Health Professionals Follow-Up Study, involving nearly 50,000 men, is a result of a shutdown in the body’s production of a certain form of vitamin D in response to too-high calcium levels; that form of vitamin D has been thought to protect against prostate cancer.
“These are associations. You can’t prove cause and effect, but it’s quite striking that we saw an increased risk for both calcium supplements and milk,” he said. While this same study’s weaker finding about the possible protective effect of lycopene in tomatoes against prostate cancer has gotten a lot of media interest, Giovannucci said he has been surprised that this 4.5-fold increased risk in metastatic prostate cancer for men with the highest calcium consumption hasn’t generated the same attention.
