Milk – Does It Really “Do A Body Good”?

We’re all familiar with food advertising and perhaps especially as it pertains to milk.  Milk campaigns have been plentiful over the past decades and many of its slogans are very memorable.

 

Do you recall some of these classics?

• “It Does a Body Good”
• “Got Milk?”
• “Dairy for Strong Bodies and For Strong Minds”
• “Make Mine Milk”

And the latest Canadian ad campaign slogan…

• “What Can’t Milk Do?”

 

These ads and the dairy companies behind them have placed milk uppermost in our collective minds when it comes to health benefits from food.

Nevertheless, ideas are shifting in the ongoing story of milk.  The new Canada Food Guide, which once made recommendations around four basic food groups – vegetables and fruit, grain products, milk and meat – has now dropped the milk group altogether and lumped dairy foods in with other protein-containing foods.  There are now only three food groups in the Canada Food Guide – vegetables and fruits, whole grains and protein foods (1).  New and continuing research is discovering disconcerting evidence that dairy products are not as healthy as we once believed.  In fact, consuming dairy may be downright dangerous.

A review from Harvard, reviewing the available evidence regarding dairy consumption and health outcomes, was published February 13, 2020 in the New England Journal of Medicine and its conclusions might be surprising to some people (2).  The researchers state that, though intake of dairy products has long been strongly encouraged to meet nutritional needs for calcium and to reduce the risk of bone fractures, scientific evidence does not support these recommendations.  In fact, there are concerns about adverse health outcomes from dairy foods and this review advises that the role of dairy consumption in human nutrition needs to be reassessed.

The paper evaluated over 100 studies related to dairy regarding the effects of dairy consumption on growth and development, bone health, body weight, cardiovascular disease, cancer, diabetes, allergies, total mortality and environmental effects.  Let’s look at why these researchers came to their startling conclusions (2).

 

Composition of Dairy Products

Dairy production is big business and, in order to produce more product, cows are bred to increase milk production.  Specifically, they are selected through breeding to produce higher levels of insulin-like growth factor (IGF-1).  In addition, cow’s milk is high in branched amino acids (leucine, isoleucine and valine) which raise IGF-1 in people who drink the milk.  Both these factors activate pathways that promote cell replication and inhibit natural cell death which may have health consequences such as higher risks of many cancers.

Additionally, cows are pregnant with their next calf for most of the time that they are milked.  This greatly increases the levels of hormones (progestins, estrogens and others) in their milk.

 

Consuming Dairy Products and Growth and Development

Normal growth and development can be attained in children without dairy products at all.  Dairy consumption increases longitudinal growth and final height.  However, the health effects of greater adult height are complex.  Being tall is linked to lower risks of cardiovascular disease but also to higher risks of many cancers, bone fractures and pulmonary embolism.

 

Consuming Dairy Products and Risk of Hip Fracture

Low rates of hip fracture are associated with low dairy consumption.  As the authors state, “Countries with the highest intakes of milk and calcium tend to have the highest rates of hip fractures.” (2).

Studies show that calcium intake is unrelated to bone mineral density at the hip.  No significant benefit in reducing the number of nonvertebral fractures can be seen from ingesting calcium.  No evidence was found that high calcium intake during childhood is necessary to increase calcium stores for strong bones throughout life.  Studies in men found that milk intake during adolescence was associated with a 9% greater risk of hip fracture for every additional cup of milk consumed per day.

 

Consuming Dairy Products and Body Weight

No overall effects of milk or other dairy foods on body weight were observed in children or adults.   Contrary to USDA recommendations to choose reduced-fat dairy for body weight control, children were found to have greater long-term weight gain with reduced-fat milk than with full-fat milk.

 

Consuming Dairy Products and Cardiovascular Disease

Milk has a relatively high content of potassium and it has been thought that higher milk intake might lower blood pressure.  However, study results on this topic are inconsistent.  The effect of milk seems to vary depending on what foods it is compared to.

• If dairy replaces refined carbohydrates and sugar-sweetened beverages, the outcome is likely to be beneficial.  However, if dairy replaces whole carbohydrates such as vegetables, legumes, fruit or nuts there may be a detrimental effect on blood pressure or simply no benefit observed.
• If dairy products are compared to red meat, consuming either full-fat or low-fat milk results in a lower risk of coronary heart disease and stroke.  However, if dairy products are compared to nuts or fish, consuming either full-fat or low-fat milk results in a higher risk of coronary heart disease and stroke.
• If dairy products are compared to polyunsaturated fat, dairy was associated with a higher risk of cardiovascular disease.

  

Consuming Dairy Products and Diabetes

The relationship to cow’s milk of the onset of type-1 diabetes is unclear.  In type-2 diabetes, dairy consumption is weakly associated or not associated at all with lower risk of diabetes.

 

Consuming Dairy Products and Cancer

Consumption of dairy products is strongly correlated with increased risk of breast cancer, prostate cancer (especially aggressive and fatal forms) as well as some other cancers.

Total dairy intake is associated with a greater risk of endometrial cancer, especially in postmenopausal women.  On the other hand, milk consumption is inversely related to risk of colon cancer, an effect that may be due to the calcium in milk.

 Interestingly, an observational study published only days after this review (February 25, 2020) corroborates the effect of cow’s milk on breast cancer.  This research followed over 52,000 women and found the following;

• Those who consumed ¼ to 1/3 cup of cow’s milk a day had an increased associated risk of breast cancer of 30%.
• Consuming one cup of milk daily increased breast cancer risk by 50%.
• Consuming 2 to 3 cups of milk daily increased the chance of breast cancer by 80%.
• Replacing dairy milk with soy milk reduced breast cancer risk by 32% (3).

 

 Consuming Dairy Products and Allergies/ Intolerance

Milk consumption seems to worsen the tendency to develop conditions such as asthma, eczema and food allergies.  Conversely, consuming soy milk leads to a lessening of symptoms of intolerance or allergy.

 

Consuming Dairy Products and Total Mortality

When milk intake was compared to consumption of other foods, dairy was associated with;

• Lower mortality than that from eating processed meat and eggs
• Similar mortality to that from unprocessed red meat, poultry and fish
• Significantly higher mortality than that from plant-based sources of protein.

 

Consuming Dairy Products and the Environment

Dairy production is responsible for 5 to 10 times more greenhouse gas production and climate change, water use, pollution and antibiotic resistance than the equivalent amount of protein from grains or legumes.  Limiting dairy production would help to reach international greenhouse-gas targets.

 

Conclusions

All the nutrients offered by milk can be obtained from other sources as has been the case for many traditional societies around the world who have low or no intake of dairy products.

Evidence does not support high dairy consumption for reduction of fractures in adults, nor has it been clearly related to weight control or risks of diabetes and cardiovascular disease.

Milk intake causes increased final height.  Being taller is linked to higher risk of fracture in the hip and other bones.  There is also an association of greater height with the increased risk of cancer.

High dairy consumption is likely to increase the risk of some cancers including prostate and endometrial cancer and reduce the risk of colorectal cancer.

There is no clear benefit of consuming low-fat dairy over whole-fat products.

Reported health effects of dairy foods depend on the foods to which they are compared;

•  Compared with refined carbohydrates, processed or non-processed red meat or sugar-sweetened beverages,  dairy appears to be healthier
• Compared to whole carbohydrates (vegetables, legumes, fruits or nuts), plant-protein sources and  polyunsaturated fat or fish, consuming dairy products is linked to detrimental outcomes including greater risk of high blood pressure, coronary heart disease, stroke and other cardiovascular disease.

Results in children are less clear.   If mother’s milk is not available, cow’s milk may be a valuable substitute early in life.  The nutrients from milk may also be beneficial in regions with poor diet quality and low energy intake.  However, in areas with adequate nutrition, high milk consumption can increase the risk of fractures later in life.

Calcium, which occurs naturally in dairy foods, and Vitamin D, which is added to many dairy products, are two important nutrients offered by dairy foods. Both nutrients are easily obtained from other foods or supplements without the potential negative consequences of ingesting dairy products.  Good alternate sources of calcium include beans, broccoli, kale, tofu, nuts and fortified orange juice.  Vitamin D supplements are inexpensive and more than adequate alternatives to dairy.

Finally, it appears that calcium needs have been overstated.  The authors of this review point out that daily calcium recommendations vary widely among different countries.  For example, the US daily calcium recommendation in adults is 1000 mg whereas the UK recommends only 700 mg daily and the WHO (World Health Organization) endorses 500 mg daily.  Additionally, our bodies can increase the amount of calcium that is absorbed from the diet when the dietary level is low.  Trials of calcium supplements have found that supplements of 1000 to 2000 mg a day resulted in a 1 to 3% greater bone density compared to placebo but this variation was not sustained over the long term.  After a year there was no difference in the bone density of women taking the supplement compared to those taking a placebo.

In the vast majority of circumstances, current recommendations for consumption of dairy foods do not appear to be justified.  One exception might be in regions of very low diet quality.  When diet quality is adequate, milk offers little in benefits and significant harms are possible.

 

 

SOURCES:

 1  https://food-guide.canada.ca/en/

2  Willett, W.C., Ludwig, D.S. Milk and health. N Engl J Med. 2020;382:644-654.

3  Fraser,G.E., Jaceldo-Siegl, K., Orlich, M., Maschak, A., Sirirat, R., Knutsen, S. Dairy, soy, and risk of breast cancer: those confounded milks. Intl J Epid. Published online February 25, 2020.