Weighing the costs and benefits of milk consumption: Should kids drink cow’s milk?

© 2009 - 2013 Gwen Dewar, Ph.D., all rights reserved

Should your kids drink milk? There are many benefits of milk consumption.

• For families who rarely or never eat meat, milk and milk products may represent important sources of protein

• Milk can boost calcium and vitamin D levels--both crucial for development and for the prevention of disease

• Milk stimulates growth

• Milk may also boost cognitive performance--either because it improves general nutrition or because it specifically promotes brain growth

But milk isn't perfect.

If, like most of the world's population, you are lactose intolerant, you need to avoid consuming cow's milk products that are uncooked or unfermented.

More universally, all people, regardless of their capacities to digest milk sugar, have reason to restrict their intake of milk and milk products:

Cow’s milk is NOT recommended for babies under 12 months

• Some milk products are high in saturated fat, and saturated fats should be restricted for kids over 24 months

• Some kids might suffer from cow’s milk protein intolerance, which causes gastric distress and other problems

• Milk and milk products can inhibit iron absorption

• Some researchers speculate that early exposure to cow’s milk might put kids at increased risk for certain diseases--like diabetes--later in life

Do these potential costs outweigh the benefits?

I doubt it--not if we’re talking about 1 or 2 daily servings of low-fat yogurt or milk for a kid who is at low risk for developing diabetes.

But don’t take my word for it. Here is an overview of the scientific evidence for--and against--the consumption of cow’s milk.


Dairying in anthropological perspective

For thousands of years, milk has been an important source of protein, fat, and calcium for many people...and not just for people in Europe, India, and the Middle East.

From the steppes of Mongolia to the highlands of East Africa and Peru--wherever, in fact, humans have herded cattle, goats, horses, camels, or llamas--humans have added milk products to their diets.

Indeed, the benefits of milk and dairy farming may have given some populations a big evolutionary advantage. Recent genetic analyses suggest that the hunter-gatherers of Neolithic Europe were replaced by dairy farming newcomers around 8,000 years ago (Malmström et al 2009; Bramanti et al 2009).

But traditions—even apparently adaptive traditions—don’t always reflect what is ideal for an individual’s long-term health and well-being.

Skeletal analyses of early farmers are case in point. Compared with hunter-gatherers, these farmers were malnourished. If milk helped early farmers replace hunter-gatherers, it may have done so because it allowed parents to wean their kids from human milk relatively early--i.e., before the age of 3 years. This would have increased the birth rate, but the new agricultural diet didn’t necessarily improve anyone’s quality of life.

More generally, we have to remember that diets—traditional or otherwise-- are always constrained by what’s available. In the civilizations of the ancient Mediterranean, people drank wine or beer instead of water. A good idea? Not if you have safe, clean water to drink. But they didn’t. So the benefits of drinking alcohol outweighed the potential risks.

Where does that leave milk? Research suggests that milk consumption may benefit many children. But milk consumption may have costs, too. Whether or not milk is a good choice depends on how you weigh these costs and benefits. It also depends on what other dietary options you have.


Benefits of milk consumption

Fortified milk and milk products are important dietary sources of calcium, vitamin D, vitamin A, vitamin B12, and other micronutrients. In fact, studies suggest that milk consumption can play a crucial role in maintaining calcium levels and vitamin D stores (e.g., Maguire et al 2012; Vissers et al 2011), and these nutritional benefits may have major health consequences.

Recent research suggests that vitamin D insufficiency is a risk factor for a variety of diseases, including heart disease, diabetes, cancer, and multiple sclerosis (Holick et al 2005). If so, vitamin D-fortified milk may help children avoid developing such diseases.

Similarly, milk consumption--by increasing calcium intake--may protect people from developing hypertension, kidney stones, insulin resistance syndrome, obesity, cancer, and even lead poisoning (Nicklas 2003).

And of course the protein and calcium in cow's milk may contribute to better overall nutrition and bone health. As summarized by Janet Rich-Edwards and colleagues (2007), studies show that children who consume cow's milk products have

• Reduced risk of protein malnutrition

• Fewer dental cavities

• Increased mineral content in their bones and fewer bone fractures

• Reduce risk of developing rickets

Much of the research concerns correlations, but there is experimental evidence, too. For example, one randomized, controlled study gave Chinese school girls 330 mL of cow’s milk per day. After two years, these girls enjoyed small but statistically significant increases in bone mineral content and bone density compared with girls in a control group (Du et al 2004).

More than good bones and teeth

The benefits of milk consumption for bones and teeth may not seem surprising. But there are less well-known benefits There is also evidence that milk consumption--by increasing calcium intake--protects people from a variety of dangerous medical conditions, including hypertension, colon cancer, breast cancer, ovarian cancer, kidney stones, insulin resistance syndrome, obesity, and lead poisoning (see Nicklas 2003 for a review with full references).

Growth: One of the benefits of milk consumption?

Milk consumption appears to promote growth, too.

For example, in the Chinese study mentioned above, the milk-supplemented girls were taller than controls. And many other studies have documented a correlation between cow’s milk consumption and height in children (Hoppe et al 2006).

This is true in developing countries—where adding milk to the diet helps eliminate nutritional deficiencies. But it’s also true in places where basic nutrition is already pretty good.

For instance, a U.S. study found that preschool children who were in the top 25% for milk consumption were about a centimeter taller than their peers (Wiley 2009). Another U.S. study found that milk consumption was linked with taller teenagers, even after controlling for age, sex, household income, and ethnicity (Wiley 2005).

How does cow’s milk promote growth?

Possibly, milk drinkers grow more because they are getting more protein. But there might be more going on. Cow’s milk is a natural source of growth hormone (GH) and insulin-like growth factor. So some researchers suspect that milk consumption promotes growth by increasing circulating levels of GH and IGF-I.

In support of this idea, some surveys have documented a link between greater milk consumption and higher levels of GH and IGF-I.

And there’s experimental evidence, too. In one study, researchers gave urban Mongolian school children supplements of whole milk and tracked their serum levels of GH and IGF-I. After a month of milk drinking, the kids experienced marked increases in GH and IGF-I levels (Rich-Edwards 2007). Similar results have been reported in China (Zhu et al 2005) and Britain (Cadogan et al 1997).

Milk and intelligence?

In addition to better bones and taller kids, milk may also be associated with smarter kids.

For example, when 7-and 8-year-old kids from rural Vietnam were given milk supplements, they scored better on short term memory tests than did kids in a control group (Lien do et al 2009).

This might reflect an overall improvement in nutrition. But there is also the possibility that milk enhances intelligence via growth factors. According to this idea, growth factors in milk boost brain development as well as linear body growth.

Intriguing? Yes. But the evidence isn’t yet there. One study found a link between IQ scores and circulating IGF-I levels in 8- and 9-year olds. However, the study didn’t measure milk consumption, and the IQ effect was not statistically significant after other variables—like maternal education—were taken into account (Gunnell et al 2005).


The potential costs of milk consumption

There are several potential costs of drinking milk. Some seem pretty clear-cut. Others are controversial.

Cow’s milk is NOT good for babies under 12 months

Cow’s milk differs from human breast milk in several important ways. For instance, cow’s milk has more protein, sodium, and potassium than is healthful for human babies. And it lacks certain essential fatty acids that human babies need for optimal development.

Moreover, some infants can’t digest cow’s milk protein very well, and it makes them ill.

So giving cow’s milk to babies is not a good idea. It can cause malnourishment and illness. For these reasons, the American Academy of Pediatrics (AAP) does not recommend cow’s milk—even whole cow’s milk—for babies under 12 months.

Some kids have lactose intolerance and/or cow’s milk protein intolerance

Both lactose intolerance and cow’s milk protein intolerance are associated with symptoms of gastrointestinal distress. But they have different implications. People who suffer from lactose intolerance need not avoid all milk products. Fermented milk products, like yogurt and cheese, are usually acceptable. By contrast, people who suffer from cow’s milk protein intolerance need to avoid most milk products.

Milk is an iron absorption inhibitor

Experiments demonstrate that the high calcium content of milk can interfere with a child’s absorption of iron, another mineral that is crucial for development. To ensure your child isn’t iron deficient, it’s a good idea to avoid serving milk products and iron-rich foods in the same meal. It may also be a good idea to limit total milk intake in young children to two cups per day (Maguire et al 2013). For the details, see this article on iron-rich foods.

Kids should limit their intake of saturated fat

Many milk products are high in saturated fats. Is this a problem? It depends on your child’s age.

Human breast milk is high in saturated fats (Giovannini et al 1994), and babies need relatively high levels of fat in their diets for proper brain development. So if you want to give an older baby cow’s milk, the American Academy of Pediatricians (AAP) recommends that you give him whole milk—not skim milk or reduced-fat milk.

For kids over 24 months, these AAP recommends that no more than 10% of daily calories should come from saturated fats.


Speculation: Does IGF-1 have a dark side?

Here's the controversial part. Remember IGF-1, the insulin-like growth factor mentioned above? It stimulates growth. But it also stimulates the production of insulin. Studies show that people who consume milk protein experience a post-meal spike in insulin levels.

This has raised the concern that early milk consumption could “program” the body produce chronically elevated levels of IGF-1, which might contribute to development of diseases associated with higher insulin levels—diseases including diabetes, adult heart disease, and cancer (Melnik 2009).

But does research to support the idea? So far, the evidence isn’t very compelling. In fact, some studies suggest that milk consumption may be more likely to protect kids from disease.

For example, a study of Lithuanian children has reported that babies given cow’s milk-based formula in the first 3 months were more likely than others to become diabetic (Skrodeniene et al 2008). But this study didn’t randomly assign babies to receive cow’s milk formula, so it’s possible that babies receiving cow’s milk were more likely to have other risk factors for diabetes.

When Finnish researchers conducted a randomized study, they did not find that cow’s milk consumption increased diabetes risk (Savilahti and Saarinen 2009). In fact, there was a trend in the other direction: Babies who were given cow’s milk-based formula were actually less likely to develop diabetes.

Similarly, a nationwide study of German preschoolers found that preschoolers who drank more cow’s milk were less likely, not more likely, to develop diabetes (Rosenbauer et al 2007).

Research on adults has reported similar results. In studies that have controlled for overall diet, body mass index, and physical activity level, adults who consumed more low-fat milk products were less likely, not more likely, to develop insulin dependence or diabetes (Choi et al 2005; Tremblay and Gilbert 2009; German et al 2009).

As for other diseases, studies of adults suggest low-fat milk products might reduce the risk of high blood pressure. (Wang et al 2008; Appel et al 1997). Increased adult milk consumption may be linked with higher rates of nonaggressive colon cancer (Ahn et al 2007). But studies have failed to find a consistent link between adult milk consumption and breast cancer (Pala et al 2009).

Why the mixed results?

I don't know. But there are several things that might make it difficult to tease apart the effects of milk consumption on health.

First, studies suggest that people suffering from vitamin D deficiency are at higher risk for diabetes (e.g., Huang et al 2012). And other ingredients in milk--like calcium--are known to protect people from developing diabetes and heart disease. So even if IGF-1 has a negative effect, the net effect of milk consumption may not be negative.

Second, it’s possible that our genes are involved. Cow’s milk consumption may more likely to trigger diabetes in kids who are already genetically predisposed to develop diabetes. This idea is consistent with the results of a Finnish study (Virtanen et al 2000). If genetics play a role, then studies might report different outcomes depending on the genetic backgrounds of people being tested.

Third, the effects of milk may depend on which cows made the milk. Researchers from Iceland analyzed the milk produced by cows from different Scandinavian countries (Thorsdottir et al 2000). Compared with cow’s milk from other countries, Icelandic cow’s milk had the lowest levels of beta casein A1 and B (proteins thought to trigger diabetes) and the highest levels of immunoglobulin (a protective antibody). This might explain why Type 1 diabetes less common in Iceland.

The bottom line?

When it comes to insulin-related diseases, milk may have both healthful and negative effects. More research is needed.

Meanwhile, parents with kids at high risk for diabetes should talk to their doctors about the effects of milk consumption.

But doesn't milk make you fat?

I've heard this claim from Hollywood celebrities, but it's not well-supported by research. Most studies, including a recent observational study tracking the development of kids in Hong Kong, have reported no links between milk consumption and excess body fat (Lin et al 2012).

What about homogenization?

Commercial milk is homogenized, and some people speculate that the process might have harmful effects. The idea is that homogenization--which reduces the size of fat droplets in milk--might put consumers at greater risk of heart disease or diabetes. Unfortunately more research is needed to evaluate this hypothesis (Michalski et al 2007).

...and what about raw milk?

Pasteurized milk is milk that has been heated to kill may disease-causing bacteria. “Raw milk” refers to milk that has not been pasteurized.

Although some people have claimed that raw milk offers special health benefits, there is, as yet, little scientific evidence to support this claim. And the fact remains that raw milk is much more likely than pasteurized milk to be contaminated with dangerous pathogens (Lejeune JT and Rajala-Schultz 2009).



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