If no one really knows the best daily calcium target, then why not play it safe and boost your calcium by drinking three glasses of milk a day? Here are six good reasons: lactose intolerance, saturated fat, extra calories, unneeded hormones, a possible increased risk of prostate cancer, and a possible increased risk of ovarian cancer.
• Lactose intolerance. All babies are born with the ability to digest milk. Some, especially those of northern European ancestry, keep this trait for life. Most children, though, gradually lose it as their bodies stop making an enzyme called lactase that breaks down milk sugar (lactose). In fact, only about a quarter of the world’s adults can fully digest milk. In the United States, as many as ﬁfty million Americans aren’t equipped to digest milk. Half of Hispanic Americans, 75 percent of African Americans, and more than
90 percent of Asian Americans can’t tolerate a lot of lactose. For them, drinking a glass of milk can have unpleasant consequences, such as nausea, bloating, cramps, and diarrhea.
A lot of eﬀort has gone into helping lactose-intolerant people drink milk or eat cheese or ice cream. The U.S. Agriculture Research Service touts its development of the lactose-modiﬁed milk known as Lactaid as one of its top ﬁfteen accomplishments in the last ﬁfty years. A variety of lactose-digesting powders or tablets that can be added to milk or taken before eating dairy products are available over the counter. And dairy proponents point to a number of studies showing that people who have trouble digesting lactose can tolerate small amounts throughout the day, especially when taken with other food. But because there are easier ways to get enough calcium, I don’t believe that people who have trouble digesting lactose need to spend the extra money or time to drink milk or eat dairy products. It is perfectly ﬁne if you want to do that. But you shouldn’t force yourself to do it or feel guilty if you don’t. After all, you’re in good company, with three-quarters of the world’s adults.
• Saturated fat. An eight-ounce glass of whole milk contains almost 5 grams of saturated fat, or about 20 percent of the recommended 20-gram daily limit. Drinking three glasses a day would be the equivalent of eating twelve strips of bacon or a Big Mac and an order of fries. Cheese is another way to get calcium. A one-ounce serving of cheese made from whole milk delivers about two-thirds of the calcium as a glass of milk and the same amount of saturated fat. If you enjoy milk, low-fat and skim are certainly better choices than whole milk.
learn more: You Are What You Drink
If enough people make the switch to low-fat or skim milk, you might expect that lower rates of heart disease would follow. They won’t, at least not at the population level. That’s because once a cow is milked, the fat from that milk is in the food supply, and someone ends up drinking or eating it. Much of the fat skimmed from milk resurfaces in premium ice cream, buttery pastries, and high-fat snack foods. Many of the same people who have switched to skim milk have a bowl of high-fat Ben & Jerry’s or Häagen-Dazs ice cream before going to bed, and people who drink whole milk or don’t drink milk at all—often poorer, less educated, or less health-savvy people—are eating more and more high-fat products made with milk fat.
• Extra calories. Three glasses of whole milk a day add 450 calories to your diet—about one-quarter of your daily intake allowance. Low-fat milk, at 330 calories, adds a bit fewer, but that is still a lot if the main goal is just to get more calcium.
• Extra hormones. Cows make most of the same hormones that humans make. Before farming turned into agribusiness, the hormone levels in milk weren’t an issue. Today, though, they may well be a cause for concern.
Over the years, dairy cattle have been bred to produce more milk. Since 1960, American Holstein cows’ genetic potential for milk production has increased nearly seven thousand pounds for each period of lactation. Cows are also routinely milked while they are pregnant, which also keeps milk production high. This is great for cattle farmers and milk producers, and it helps keep the price of milk relatively low. But it also means that today’s milk contains a more concentrated hormonal stew than it did years ago. Naturally occurring hormones in milk include estrogens and progestins, androgens, and insulinlike growth factors, to name just a few. Estrogens and progestins can stimulate breast cancer, androgens promote prostate cancer, and elevated levels of insulinlike growth factor have been linked with breast, prostate, and colon cancer.
Almost ten years ago, my colleagues and I started the Growing Up Today Study among children of women in the Nurses’ Health Study. The more than sixteen thousand volunteers complete forms on diet, exercise, lifestyle factors, and health much as their mothers do. In this group, the largely hormone-driven condition of teenage acne is more common among milk drinkers. This is important because it suggests that the hormones in milk are strong enough or abundant enough to stimulate glandular tissue such as the sebaceous glands in the skin—and possibly mammary glands in the breast.
• Prostate cancer. A diet high in dairy products has been implicated as a risk factor for prostate cancer. In nine separate studies, the strongest and most consistent dietary factor linked with prostate cancer was high consumption of milk or dairy products. In the largest of these, the Health Professionals Follow-up Study, men who drank two or more glasses of milk a day were almost twice as likely to develop advanced or metastatic (spreading) prostate cancer as those who didn’t drink milk at all.
At ﬁrst, researchers thought that the connection between dairy products and prostate cancer was due to the saturated fat in dairy products. But results from the Health Professionals Follow-up Study, as well as more careful analyses of other data, suggest that calcium might be the main culprit. In this study, men who took in more than 2,000 mg of calcium a day from food and supplements combined were almost three times as likely to develop advanced prostate cancer and more than four times as likely to develop metastatic prostate cancer than men who got less than 500 mg/day.
learn more: WHY YOU NEED CALCIUM
There’s a plausible explanation for this. Inside the prostate (and elsewhere), the active form of vitamin D may act like a brake on the growth and division of cancer cells. Too much calcium slows or even stops the conversion of inactive vitamin D to its biologically active form and so may rob the body of a natural anticancer mechanism.
To be on the safe side, men should try to keep their daily calcium intake below 1,000 mg.
• Breast cancer. Early-onset breast cancer (cancer that appears before menopause) seems to be associated with high intake of full-fat dairy products. This is especially the case for estrogen-receptor positive (ER+) breast cancer, in which estrogen stimulates cancer cells to grow and divide.
• Ovarian cancer. About ﬁfteen years ago, Harvard Medical School researchers suggested that high levels of galactose, a simple sugar released by the digestion of lactose in milk, could damage the ovary and possibly lead to ovarian cancer. Since then a number of studies have tested this hypothesis. While the evidence isn’t conclusive (some studies have supported this notion and others haven’t), a ositive link between galactose and ovarian cancer shows up too many times to ignore the possibility that it may be harmful.
The ideal prevention strategy is one that stops something bad from happening without causing any other bad things to happen. Consuming plenty of dairy products is being portrayed as a key way to prevent osteoporosis and broken bones. But not only does this fail to ﬁt the bill as a proven prevention strategy, it doesn’t even come close. The totality of evidence doesn’t support the claim that just getting more calcium prevents fractures over the long term, and there is plenty of evidence that drinking two or three glasses of milk a day does little to reduce the chances of breaking a bone. What’s more, dairy products pose several proven and potential problems. So if you are worried about osteoporosis, other prevention strategies make better sense.