Milk: What the Scientific Evidence Says

by Disha Gandhi

This past summer, I had the opportunity to complete an internship with the National Dairy Council in Rosemont, IL. It was a wonderful experience and definitely opened my eyes about the dairy industry. My project was to review the literature on milk and now I am sharing what I learned with you.

The Decline of Milk

Milk consumption has been steadily declining in the US: in 1970 individuals drank about 0.96 cups/day while in 2013 consumption decreased to 0.61 cups/day. The advent of sugar sweetened beverages and energy drinks may be related to this decline. Essentially, beverages that are not as nutrient rich are replacing milk. Low fat milk contains protein, calcium, potassium, vitamin B12, vitamin D, and yet it continues to be stigmatized. It is my goal to de-stigmatize milk by addressing some health benefits and debunking common health-related myths.

A Misconception About Milk

One of the major misconceptions about milk is that it may contain antibiotics. Farmers care about their cows and want to keep them healthy.  Thus, antibiotics are used to fight infections when needed. When a cow is on an antibiotic treatment her milk is discarded. As an added precaution, milk is tested for antibiotic residues before it enters the processing plant and positive results require the entire tanker of milk to be discarded. If tainted milk somehow does make its way to the processing plant then the farmer who is responsible for this mistake is also financially responsible for all of the milk that was lost. This is a long-standing standard practice.

Does Milk Increase the Risk of Chronic Diseases?

The 2010 Dietary Guidelines for Americans (DGA) state, “moderate evidence indicates that intake of milk and milk products is associated with a reduced risk of cardiovascular disease, type 2 diabetes, and lower blood pressure in adults.” The majority of the evidence pertains to studies assessing dairy as a whole (milk, cheese, and yogurt combined); therefore we cannot tease out the effect of milk alone. Furthermore, a very limited number of studies, including randomized controlled trials (RCTs), have examined the health outcomes associated with consuming only milk.

After completing an exhaustive literature review on milk and its relation to various health outcomes for my internship at National Dairy Council, here is some of what I found:

Milk and Heart Disease

Overall milk consumption was not associated with cardiovascular disease (CVD) and was even shown to be protective. Additionally, a meta-analysis of 10 observational studies determined that subjects that drank milk in greater amounts compared to the subjects that drank much less was associated with a small reduction in heart disease, concluding that there is no evidence that milk consumption is harmful to cardiovascular health.

When interpreting these data it is important to note that observational studies show an association—not causation—and therefore we must look at RCTs to obtain more evidence. In a 2015 crossover RCT conducted on 27 post-menopausal women with abdominal obesity, results showed that consuming 2% milk 3 times a day for 6 weeks had no impact on LDL cholesterol levels and that changes in HDL cholesterol were similar to the control National Cholesterol Education Program diet (no milk or dairy). The authors concluded that in these at risk women, milk consumption had neither favorable nor adverse effects on a wide range of cardiac risk factors.

Milk and Type 2 Diabetes

Milk is a low glycemic index (GI) beverage meaning that blood glucose levels will be significantly lower than post consumption of a high glycemic food such as white bread (GI=100). However, in 2001, researchers in Sweden demonstrated that milk raised insulin levels as high as white bread. Additional studies have suggested that whey protein may be responsible for the insulinotropic effect of milk. This effect may provide a benefit to individuals diagnosed with type 2 diabetes by helping to stabilize glucose levels in type 2 diabetics, although additional research is needed. While these mechanisms should be investigated further, a recent meta-analysis suggested that the dairy food group is inversely associated with the risk of type 2 diabetes with milk having a null association.

Milk and Bone Health

Dr. Walter Willett’s 2014 observational study on milk consumption and hip fracture risk revealed that every additional cup of milk consumed during teenage years was associated with a 9% increased risk of hip fractures in men (40-75y). One of the limitations of this study was that participants had to recall their milk consumption from childhood and adolescence, which leads to inherent errors in reporting. Additionally, we cannot make recommendations based on a single study, so we have to examine more literature on this topic.

  • In 2003, data from NHANES 1988-1994 showed that non-Hispanic, white adult women who drank >1 serving milk per day during adolescence had greater bone mineral content (BMC) and density (BMD) compared to women who drank <1 serving milk per week. Again, these women were asked to recall their milk consumption levels during adolescence from memory.
  • An intervention trial conducted on 12-year-old girls found that those who were randomized into the milk group (2 servings/day of skim or 1% milk) had a significantly greater increase in BMD and BMC compared to the control group (usual diet).

Furthermore, the 2010 DGA concluded that moderate evidence shows that intake of milk and milk products is linked to improved bone health, especially in children and adults. Milk and milk products contribute many nutrients to the American diet, including calcium and vitamin D, which help build and maintain strong bones.

After reviewing the current scientific literature on milk and its impact on various health outcomes (heart disease, type 2 diabetes, bone health, weight loss, blood pressure, and cognition), the overall results have shown that milk may have protective and/or neutral effects towards these health outcomes. However, more RCTs in a variety of populations are needed to obtain a better understanding of milk and its associated health outcomes. In the meantime, I am going to continue adding milk to my Indian masala chai and other desserts, and of course as part of a healthy diet. While I was not able to address every concern about milk and dairy, I hope this information has been helpful and provided you with newfound knowledge about milk.

Disha Gandhi is a second year MS Candidate in BMN. In her free time when she is not doing Nutrition related work, she is still thinking about food and trying out different restaurants around Boston. Please follow her on twitter @DishaG318.

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