Is Drinking Milk Good or Bad for You?Posted: May 31, 2010
The Milk Debate Keeps Churning
At one time, milk was promoted as “the perfect food.” Breast milk, of course, might be called the perfect food for an infant, but otherwise no one food is perfect or sufficient in itself. Still, milk and dairy products are very nutritious and the chief source of calcium in the American diet. They offer many benefits as part of a heart-healthy diet and are an essential component of the DASH diet, designed to control blood pressure. After decades of research, we know a great deal more now about milk. But legitimate questions, plus a number of myths, have multiplied.
The arguments about milk are highly politicized, with the dairy industry on one side and milk opponents on the other. Still, there is plenty of well-designed research, including some sponsored by the dairy industry and some from independent researchers. Here are answers to questions you may have.
Does drinking cow’s milk cause cancer? Or protect against it? I’ve heard both these claims.
There’s no clear link between milk and cancer—one way or the other. Dairy opponents say that milk increases the risk of breast, prostate, and ovarian cancer. A few studies support this idea, but other studies have not found any increased risk. In addition, milk may actually reduce the risk of colon cancer, because of its calcium and vitamin D. For example, a study in the British Journal of Nutrition in 2006 found that people who drank very little milk had a somewhat higher risk of colon cancer than those who drank at least a glass a day.
Should I avoid milk with rBST, the hormone some producers inject into dairy cows? I read this was a cause of early sexual development in girls.
Recombinant bovine somatotropin (rBST) is a growth hormone for cows, identical to the hormone they produce on their own. Cows injected with rBST produce more milk from the same amount of feed. This has ecological benefits: fewer cows making more milk saves feed, water, and farmland. It also might help reduce milk prices. But it makes cows more vulnerable to mastitis (an udder infection) and thus may require cows to be treated with antibiotics. There is no evidence that milk from cows injected with rBST is harmful to humans. Their milk is the same as any other milk—no chemical difference can be detected. All foods contain hormones naturally, and all milk contains BST. Still the public has been wary, and some producers now advertise that their milk comes from untreated cows and strongly imply it is safer. You can buy untreated milk if you wish, but there is no reason to fear rBST.
As for the early sexual development of girls, it is true that the age of menarche (onset of menstruation) has been gradually declining in the U.S. in the past century. In the mid-1990s (the latest data), menarche occurred a few months earlier (by as much as a year in some ethnic groups) than in the 1920s. No one knows what this means or why it is happening. But growth hormones in milk, in use only since the mid-1990s, are obviously not the cause. Better nutrition or the increasing levels of obesity among children may be at least partly responsible.
Does milk help prevent osteoporosis? Or cause it, as some milk opponents claim?
Some anti-milk groups claim that dairy products actually increase the risk of osteoporosis, the severe loss of bone mass that often accompanies aging. They point to the fact that in most parts of China and India, where dairy products are rarely consumed and calcium comes primarily from green vegetables, the rate of osteoporosis and fractures is much lower than in the U.S., where dairy consumption is high. But it’s not possible to blame these national differences in bone health solely on dairy intake, since genetic, cultural, and life-style factors, as well as other dietary ones, undoubtedly also come into play. It is highly unlikely that drinking milk causes osteoporosis.
One possible problem with dairy products is that they are rich in protein—and a very high protein intake slightly increases calcium excretion in urine and might reduce bone density. However, adequate protein helps keep bones strong, and the high levels of calcium in dairy products may more than offset the small adverse effect their protein may have on bones. In addition, milk is almost always fortified with vitamin D, which may be at least as important as calcium for bone health, according to recent research.
Bone loss is caused by many factors besides diet. According to noted calcium researcher Dr. Robert Heaney, of Creighton University in Omaha, the great majority of studies show that calcium from dairy products has a protective effect on bones. Getting calcium from milk may provide longer-lasting benefits than getting it from supplements. Milk contains other nutrients important for bones besides calcium and vitamin D, such as magnesium, phosphorus, and potassium. In the grand scheme of factors affecting bone health, dairy and calcium intake after early adulthood probably plays only a small beneficial role. But don’t believe claims that dairy products harm your bones.
What about milk and heart disease?
If you consume lots of whole milk, whole-milk yogurt, and cheese, you may see your blood cholesterol levels rise, especially if these foods contribute to weight gain. But you can get dairy products in nonfat or low-fat versions, which are lower in calories. There is evidence that increased intake of milk is linked with a reduced risk of stroke and heart attack. Certain substances in milk may even help lower cholesterol. As noted earlier, nonfat or low-fat dairy products are an important part of the DASH diet and can thus help lower high blood pressure.
Is milk the cause of acne in adolescents?
For many years, teens and their parents have blamed diet for outbreaks of acne—chocolate being the prime suspect. But most experts do not think that specific foods play a role. Still, some dermatologists disagree, and some blame milk. The theory is that the hormones in milk interact with human hormones and cause pimples. In 2008 in the Journal of the American Academy of Dermatology, Harvard researchers presented preliminary evidence that drinking skim milk was associated with acne in young boys. There was no explanation for why only skim milk, not whole milk, would have this effect.
Can milk help you lose weight?
Some studies have suggested that milk (or its calcium) can help people lose weight or at least prevent weight gain. A few years ago the dairy industry trumpeted this possibility in ads, but the USDA told it to stop. Even the positive studies, mostly funded by the industry, showed only very small benefits over long periods.
Is it important to drink organic milk?
As far as nutrition and safety are concerned, studies have consistently found no difference between organic and conventional milk. A study in the .Journal of the American Dietetic Association in 2008 concluded that the differences are few and minor Batches of milk tested may vary—organic milk may have higher (or lower) levels of nutrients, compared to conventional. The composition of milk varies according to the diets of the cows and other factors, and from season to season. Organic milk often costs twice as much. If you feel you are voting for better agricultural practices, and you can afford the high price, that’s a reason to buy it. Whatever you do, always buy pasteurized dairy products, since raw milk is dangerous.
Does milk increase mucus production when you have a cold?
Studies have found no connection between milk and mucus formation. This idea persists because whole milk tends to coat the mouth briefly. If you don’t like this quality of whole milk, that’s yet another reason to switch to low-fat or nonfat milk. If you find milk unpleasant when you have a cold or cough, stop drinking it until you feel better.
What about people who are lactose-intolerant?
People who have difficulty digesting lactose (the sugar in dairy products) can consume lactose-reduced products or else take pills containing lactase (the enzyme that breaks down lactose) beforehand. Yogurt tends to be less of a problem, since the bacteria in it break down some of the lactose. Still, if you don’t like dairy products, or they don’t like you, you need not eat them. All it takes is a little planning—see “Speaking of Wellness” below.
And if you won’t drink your milk . . .
By Dr. John Swartzberg
People have always had strong feelings and beliefs about food. Take tomatoes. A major world crop that nearly everybody eats (and many of us grow), tomato plants were introduced from South America to Europe in the 1600s, perhaps by the Spanish. The Italians named the tomato pomodoro, or golden apple (the first ones were yellow), and thought they had aphrodisiac powers. Others deemed them poisonous, and for many years they were only grown ornamentally. In this country, their bad reputation persisted long after Europeans had learned to eat them, but Thomas Jefferson (a devoted gardener) grew them for food and recommended them. Since they are part of the nightshade family, some people continue to regard them with suspicion.
Milk, too, has long had its detractors. Before pasteurization and refrigeration, dairy could truly be dangerous. Lately, cow’s milk has been blamed for everything from excess mucus production to heart disease. One of the most curious current myths about milk is that there is something inherently unnatural about drinking the milk of another species and that therefore it causes disease. But all foods from animals come from species other than ourselves. Indeed, plants are also “other species.” What else would we eat?
For most people, dairy is an easy way to get calcium and other important minerals. But you can get the nutrients you need from many other sources.
In particular, if your diet consists mainly of fruits, vegetables, and whole grains, plus small portions of protein, you don’t need dairy, as long as you get adequate calcium and vitamin D from other sources. Some green vegetables (such as collards and broccoli), canned salmon and sardines (with the bones), and soybeans are fair-to-good sources of calcium. Calcium-fortified foods, such as orange juice and soy milk, are good options. If you don’t get at least 1,000 milligrams of calcium a day from food, you can take calcium supplements. Dairy is also rich in potassium and magnesium, which help prevent hypertension. But, again, you can get these minerals from other foods.
Milk is the leading dietary source of vitamin D (it is fortified with 100 IU per cup). But even if you drink milk, it may be hard to consume enough D without a supplement. The government advises 400 IU a day for people age 50 to 69, and 600 IU for those over 70. We recommend 800 to 1,000 IU a day for most people.
UC Berkeley Wellness Letter, May 2010