Those advertisements pushing milk as the answer to strong bones are almost inescapable. But does “got milk?” really translate into “got strong bones?”
source: Harvard School of Public Health
The pro-milk faction believes that increased calcium intake—particularly in the form of the currently recommended three glasses of milk per day—will help prevent osteoporosis, the weakening of bones. Each year, osteoporosis leads to more than 1.5 million fractures, including 300,000 broken hips.
On the other side are those who believe that consuming a lot of milk and other dairy products will have little effect on the rate of fractures but may contribute to problems such as heart disease or prostate cancer.
When most people in the United States think of calcium, they immediately think of milk. But should this be so? Milk is actually only one of many sources of calcium—dark leafy green vegetables and some types of legumes are among the other sources—and there are some important reasons why milk may not be the best source for everyone.
These reasons include the following:
Many people have some degree of lactose intolerance. For them, eating or drinking dairy products causes problems like cramping, bloating, gas, and diarrhea. These symptoms can range from mild to severe. Certain groups are much more likely to have lactose intolerance. For example, 90 percent of Asians, 70 percent of blacks and Native Americans, and 50 percent of Hispanics are lactose intolerant, compared to only about 15 percent of people of Northern European descent.
One alternative for those who are lactose intolerant but who still enjoy consuming dairy products is to take a pill containing enzymes that digest milk sugar along with the dairy product, or to consume milk that has the lactase enzyme added to it.
High Saturated Fat Content
Many dairy products are high in saturated fats, and a high saturated fat intake is a risk factor for heart disease. And while it’s true that most dairy products are now available in fat-reduced or nonfat options, the saturated fat that’s removed from dairy products is inevitably consumed by someone, often in the form of premium ice cream, butter, or baked goods.
Strangely, it’s often the same people who purchase these higher fat products who also purchase the low-fat dairy products, so it’s not clear that they’re making great strides in cutting back on their saturated fat consumption.
Possible Increased Risk of Ovarian Cancer
High levels of galactose, a sugar released by the digestion of lactose in milk, have been studied as possibly damaging to the ovaries and leading to ovarian cancer. Although such associations have not been reported in all studies, there may be potential harm in consuming high amounts of lactose. A recent pooled analysis of 12 prospective cohort studies, which included more than 500,000 women, found that women with high intakes of lactose—equivalent to that found in 3 cups of milk per day—had a modestly higher risk of ovarian cancer, compared to women with the lowest lactose intakes.
The study did not find any association between overall milk or dairy product intake and ovarian cancer. Some researchers have hypothesized, however, that modern industrial milk production practices have changed milk’s hormone composition in ways that could increase the risk of ovarian and other hormone-related cancers. More research is needed.
Probable Increased Risk of Prostate Cancer
A diet high in calcium has been implicated as a probable risk factor for prostate cancer. In a Harvard study of male health professionals, men who drank two or more glasses of milk a day were almost twice as likely to develop advanced prostate cancer as those who didn’t drink milk at all. The association appears to be with calcium itself, rather than with dairy products in general: A more recent analysis of the Harvard study participants found that men with the highest calcium intake—at least 2,000 milligrams a day—had nearly double the risk of developing fatal prostate cancer as those who had the lowest intake (less than 500 milligrams per day).
Clearly, although more research is needed, we cannot be confident that high milk or calcium intake is safe.
Adequate, lifelong dietary calcium intake is necessary to reduce the risk of osteoporosis. Consuming adequate calcium and vitamin D and performing regular, weight-bearing exercise are also important to build maximum bone density and strength. After age 30, these factors help slow bone loss, although they cannot completely prevent bone loss due to aging.
Milk and dairy products are a convenient source of calcium for many people. They are also a good source of protein and are fortified with vitamins D and A. At this time, however, the optimal intake of calcium is not clear, nor is the optimal source or sources of calcium. As noted earlier, the National Academy of Sciences currently recommends that people ages 19 to 50 consume 1,000 milligrams of calcium per day, and that those age 50 or over get 1,200 milligrams per day. Reaching 1,200 milligrams per day would usually require drinking two to three glasses of milk per day—or taking calcium supplements—over and above an overall healthy diet.
However, these recommendations are based on very short-term studies, and are likely to be higher than what people really need. Currently, there’s no good evidence that consuming more than one serving of milk per day in addition to a reasonable diet (which typically provides about 300 milligrams of calcium per day from nondairy sources) will reduce fracture risk. Because of unresolved concerns about the risk of ovarian and prostate cancer, it may be prudent to avoid higher intakes of dairy products.
At moderate levels, though, consumption of calcium and dairy products has benefits beyond bone health, including possibly lowering the risk of high blood pressure and colon cancer. (20–25) While the blood pressure benefits appear fairly small, the protection against colon cancer seems somewhat larger, and most of the latter benefit comes from having just one or maybe two glasses of milk per day in addition to what we get from other foods in our diet. Getting more than this doesn’t seem to lower risk further.
For individuals who are unable to digest—or who dislike—dairy products and for those who simply prefer not to consume large amounts of such foods, other options are available. Calcium can also be found in dark green, leafy vegetables, such as kale and collard greens, as well as in dried beans and legumes.
Calcium is also found in spinach and chard, but these vegetables contain oxalic acid, which combines with the calcium to form calcium oxalate, a chemical salt that makes the calcium less available to the body. A variety of calcium-fortified foods, such as orange juice and soy milk, are now on the market.
Calcium can also be ingested as a supplement, and if you do go the supplement route, it’s best to choose one that includes some vitamin D. Research suggests that calcium-only supplements do not protect against fractures, and may in fact increase risk of fractures. (4) There’s also some emerging evidence that taking calcium-only supplements may possibly increase the risk of heart attacks—another reason to avoid calcium-only supplements. (26) Men may want to avoid calcium supplements because of questions about possible risks of prostate cancer; if men do take a calcium supplement, limiting supplement intake to 500 milligrams of calcium per day seems prudent.
Antacids contain calcium, but do not contain vitamin D. So if you choose antacids as a calcium source, you may want to consider taking a separate vitamin D supplement. Discuss your options with a health care provider. (Read more about vitamin D and health.)
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