Drink your milk! Some of us heard that command many times growing up, and most of us never questioned it. At some point, we all learned - whether from our parents, our health science teachers, or ads on TV and in magazines - that milk from cows provides not only calcium but also vitamin D and many other nutrients with numerous health benefits. Milk does a body good, doesn't it?
A growing number of consumer advocates and scientists don't think this is necessarily true. They question the long-held wisdom of regular milk consumption, and some of these people even believe milk poses substantial health risks to humans.
What's at the bottom of this backlash? Is there any truth to what the critics are saying, or is it just a storm in a cereal bowl?
The Changing Face of Milk
Some of the controversy surrounding milk lies in the way commercially available cow's milk has changed over the years. In general, milk consists of water, fat, protein, lactose, minerals, vitamins, and enzymes. But the exact composition of milk depends on what cows eat, their cycle of lactation, the number of lactations, and how the milk is processed. Today's commercial milk-production techniques can significantly modify the end product, changing it from its natural form to something quite different.
For example, most commercially produced milk undergoes pasteurization to destroy bacteria and pathogens that may be harmful to health. However, some people claim that raw, unpasteurized milk tastes better and is more nutritious than the pasteurized variety.
Get a clearer picture of the controversy with the below Q & A.
Out to Pasture
Does pasteurization affect the nutritional value of milk?
Yes. Although pasteurization kills potentially dangerous bacteria, such as listeria, E. coli, and salmonella, it also kills off harmless and useful bacteria, such as lactobacillus acidophilus, and active enzymes that help with digestion and absorption of nutrients. Some studies also suggest that pasteurization reduces the amount of vitamins B1, B6, B12, and C contained in milk.
However, this reduction in nutrients is not significant and the risks associated with consuming raw milk outweigh the benefits.
Home on the Grain
Is the milk from grain-fed cows less healthful than the milk of grass-fed cows?
Yes. Almost all of the long-chain polyunsaturated fatty acids (PUFAs) in milk are the result of what the cows eat; when cows graze on grass and mixed greens, it improves the fat composition of their milk, equalizing the ratio of omega-6 to omega-3 fatty acids. This ratio is believed to be ideal for human health because it helps raise good cholesterol, lower triglycerides, and reduce inflammation. Research suggests that a cow raised grazing on its natural diet of fresh pasture also has five times more conjugated linoleic acid (CLA), a cancer-fighting fat.
By replacing a cow's grass diet with grain, the ratio of the essential fatty acid in the milk is greatly altered. Milk from commercially raised cows whose feed contains blood meal or bone meal has a more detrimental fatty acid composition and contains little, if any, CLA.
It's not easy to find milk products from dairies that raise cows on open pastures. Some organic dairy cows are grass-fed, but not all. Nevertheless, consumers are buying organic milk and dairy products in record numbers.
Organic or Conventional?
The U.S. dairy industry has always been quick to adopt new technology and management techniques to improve milk production and efficiency. Although the number of cows and dairy farms in the United States has declined in the past 50 years, the average herd size and milk production per cow has increased.
To increase milk production in cows, many U.S. dairy farmers inject their herds with recombinant bovine growth hormone (rBGH), also known as recombinant bovine somatotropin (rBST) and Posilac. All milk contains natural levels of bovine growth hormone, a substance produced by the pituitary gland of the cows. The United States, however, is the only country that has approved rBGH injections to increase cows' milk production.
An estimated one-third of all cow herds at conventional dairies are given rBGH injections, but the U.S. Food and Drug Administration (FDA) does not require milk producers to place any identifying labels on milk produced by cows receiving these injections. The FDA claims that rBGH has no effect in humans and declared it "safe for human consumption" in 1993.
Does research connect the hormones in rBGH-treated cows to cancer?
Yes. Critics of the hormone therapy argue that milk from rBGH-treated cows may pose a cancer risk to humans due to the elevated levels of insulin-like growth factor-1 (IGF-1) contained in it. IGF-1 is a naturally occurring enzyme in both humans and cows, but rBGH-treated cows may have as much as 10 times the normal level of IGF-1.
Research has not connected the IGF-1 levels in milk with increased cancer risk, although high levels of IGF-1 in blood have been linked to rapid cell division and the formation of cancerous tumors. Exactly how ingestion of milk products from rBGH-treated cows affects IGF-1 levels in the blood is not clear. Some studies done on rats suggest that IGF-1 can be absorbed into the bloodstream from the digestive tract, but other animal studies found that the amount of IGF-1 entering the blood stream was too small to be significant.
Then again, some research suggests that IGF-1 may not need to move to the bloodstream to pose problems; numerous IGF-1 receptors exist within the intestine, allowing it to act on the intestinal wall lining. Some researchers believe the additional IGF-1 may promote the growth of existing cancers. Given the high incidence of colon cancer in many countries, any extra IGF-1 exposure in the colon could be worrisome.
Many organic farmers now label their products "rBGH-free" to distinguish their milk products from conventional milk. This labeling has upset many in the conventional dairy industry and led to several legal battles. The farmers who use rBGH believe organic dairies are marketing a perception that the organic milk product is safer, or of higher quality, than other milk.
Milk production techniques in the United States have created some of the new concerns about milk. But research touting the health benefits of milk continues to flood the media. What about all those recent claims about dairy products boosting weight loss, a potential boon in a country of burgeoning waistlines?
Weight Loss Booster?
Recent research touts the benefits of milk when it comes to losing weight. Does including three servings of milk in the daily diet help the average person lose weight?
No. Although some studies suggest a possible role, it is not a simple case of drink milk, lose weight. In the most widely publicized studies, which were funded by the National Dairy Council, obese people who were on a calorie-restricted diet that included three to four dairy servings per day increased their rate of weight loss compared to obese people who consumed fewer dairy products.
However, the population size of these studies was too small and too specific to extend the claims about weight loss to the general population. Larger randomized trials on the dairy - weight loss connection reveal that adding dairy to the diet without restricting calories has no effect on, or actually may increase, body weight.
Although dairy may not solve your stalled weight loss program, drinking milk may help you get more results from your exercise routine. Milk provides a complete protein, which means it offers all of the essential amino acids or building blocks of protein. Dietary protein helps build and repair muscle tissue and can serve as a source of energy during high endurance exercises such as running, cycling, and other aerobic exercise.
Good for getting your muscles strong, yes. But what about strong bones? Calcium found in milk has long been touted as the key to preventing osteoporosis, a debilitating disease characterized by low bone mass and deteriorating bone tissue.
Is drinking milk daily the only key to protecting adults against osteoporosis?
No. Although your body does need calcium to build and maintain bone strength - especially when you're young - it is only one of several habits that help keep bones strong. Other important habits that may play an even more important role include getting plenty of vitamin D, not smoking, and regular physical activity, especially weight-bearing exercises.
Recent studies suggest that, as an adult, getting the recommended amount of vitamin D is as important as getting enough calcium because the body needs vitamin D to absorb calcium from food or supplements.
Although milk contains calcium and is fortified with vitamin D, there are other sources of these nutrients. You could get the calcium you need by eating lots of dark-green leafy vegetables, beans, and calcium-fortified products, or by taking enough supplemental calcium to reach your targeted intake. You can generally get enough vitamin D from fatty fish and occasional exposure to sunlight - for example, 10 to 15 minutes in the sun a few days a week during nonpeak hours without sunscreen.
Recommended Calcium Intake:
- 1,000 - 1,500 milligrams per day for adult women and men
Recommended Vitamin D Intake:
- 400 IU per day for people under 70 years old
- 600 IU per day for people over 70 years old
Some experts question whether milk should be recommended at all for osteoporosis prevention.
For example, some studies reveal that the incidence of bone fractures - the most tangible consequence of osteoporosis - is very low in countries where average daily calcium intake is as low as 300 milligrams per day.
Some milk critics claim that osteoporosis incidence is actually higher in countries that consume more daily servings of milk because milk leaches calcium from bones, making them weaker.
Although too much animal protein will leach calcium from bones, the amount that is leached depends on the ratio of calcium to protein intake in your diet. Because so many foods are fortified with calcium, it is unlikely that drinking milk in reasonable amounts would cause leaching of calcium from bone.
So although milk can be part of the prevention picture for osteoporosis, it doesn't have to be.
But there are other diseases besides osteoporosis that concern aging Americans. For example, cancer has recently surpassed heart disease as the leading cause of death for people of a certain age in the United States.
Have studies revealed that drinking milk may help lower a person's risk of developing colorectal cancer?
Yes. An analysis of data from 10 different studies revealed that milk consumption reduced the risks of rectal cancer and cancer of the distal colon, which is the portion of the colon closer to the rectum. People who drank over 8 ounces of milk per day, the equivalent of about 250 grams of calcium, had a 15% reduction in rectal cancer and distal colon cancer risk compared to people who drank less than a couple 8-ounce glasses per week. And milk reduced the risk of colon cancer more than other calcium-laden foods such as yogurt or cheese, suggesting something particular about milk produced the effect.
However, the data on such positive associations between milk consumption and colon cancer risk come from studies that were conducted before rBGH was used in milk. Additional studies are needed to determine whether today's milk shows the same results.
Don't Cry Over Spilled Milk
Overall, there is no evidence to justify claims that modern milk has any special power to improve any specific aspect of health.
Any positive effects from drinking milk are usually explained by an elevated intake of calcium or vitamin D, nutrients that can easily be found in sufficient quantities from other sources. In addition, the potential health risks posed by modern milk production techniques need further research.
If you choose to keep milk on your menu, organic milk might be a healthier choice than commercial milk given current processing practices. But if you decide to skip dairy products altogether, rest assured that there is no reason to believe milk is a necessity, as long as you eat a balanced and varied diet that includes other sources of calcium, vitamin D, and protein.
This content is reviewed regularly and is updated when new and relevant evidence is made available. This information is neither intended nor implied to be a substitute for professional medical advice. Always seek the advice of your physician or other qualified health provider prior to starting any new treatment or with questions regarding a medical condition.