Is Cow's Milk Healthy?

This article from Discover outlines a few key areas on milk and health.

On bone strength and milk consumption:

But according to a recent review from Ludwig and Harvard University endocrinologist Walter Willett in the New England Journal of Medicine, milk may not be the magic bullet for strong bones as once thought. In fact, countries that tend to consume the highest amounts of milk and calcium also have the highest rates of hip fractures. This doesn’t necessarily mean that the milk caused their fractures, but the fact that many low-dairy populations do not suffer from high rates of fracture might help put milk consumption in perspective. 

It also points out the high rates of lactose intolerance  in the US and globally and links between milk consumption and prostate cancer and endometrial cancer.  The article further talks about the complex research on heart disease and high blood pressure and the differences in race, milk consumption, and disease incidence.  

There is a healthy selection of articles reviewing the political relationship between the US dairy industry and government and how that may impact recommendations or skew research funding.

The Dairy Economics Analysis Staff as an example:

collaborate with the Economics Division, Order Formulation and Enforcement, and Federal Milk Market Administrator Offices to provide ongoing economic research and support for Dairy Program needs, and contribute to a range of agency and department-wide efforts.

Vox has contributed on a number of articles on this topic:

How Big Government Helps Sell Milk

trade groups giving millions to members of Congress and lobbying for influence over the nation's nutrition policy

Why American farmers are throwing out milk tons of milk

Since so many schools and businesses have closed due to lockdowns, dairy farmers across the country who make products for the food service industry have nowhere to send their milk.

When the cow's are away, nutrition will pay

When it comes to nutrition, milk supplies a formidable 13 essential nutrients that benefit health and wellness. It’s also an affordable choice of nutrition, especially for protein and bone health. Calcium, a key element of bone health, costs 12 cents per milligram in milk and dairy, compared to $2.45 per milligram in protein foods and $3.33 per milligram in fruit. In fact, Americans 2 years of age and older get over half of their calcium and vitamin D from milk, cheese, and yogurt, plus over a quarter of all the vitamin B12 consumed in the U.S.

https://www.nichd.nih.gov/sites/default/files/publications/pubs/documents/NICHD_MM_Lactose_FS_rev.pdf

https://www.health.harvard.edu/blog/dairy-health-food-or-health-risk-2019012515849

A large meta-analysis that reviews milk consumption with a variety of risk factors. The primary takeaways are:

This dose-response meta-analysis of prospective studies indicates that milk intake is not associated with total mortality but may be inversely associated with overall CVD risk; however, these findings are based on limited numbers.

This meta-analysis found limited health outcomes for cardiovascular disease (CVD), coronary heart disease (CHD), stroke, and all-cause mortality. The authors discuss the limitations of this meta-analysis as viable studies were limited:

This meta-analysis indicates the challenges of summarizing data on food intake from published studies. Although 17 studies with data on dairy foods were identified, only 4 studies (representing only ≈5% of the total number of subjects) provided data on milk intake and risk of CVD in a manner that could be summarized statistically....

...In 8 studies, risk of total mortality could be examined, and no association was observed with milk intake. Data on total dairy product and total high-fat and low-fat dairy product intakes did not indicate any association with incident CHD, but these results were based on very limited numbers of studies.

The study also points to no publication bias:

The funnel plot...shows reasonable symmetry and a nonsignificant Begg’s test for publication bias (P = 0.11), which suggested no evidence of publication bias in studies of milk and all-cause mortality.

From nutritionfacts.org, this video targets the impact of dairy and milk consumption on prostate cancer and colorectal cancer. Primarily, mixed cancer recommendations for dairy and milk can be understood through the conflicting negative impacts of milk on prostate cancer but protective impacts against colorectal cancer.

This video argues that metastudies such as Dairy products, calcium, and prostate cancer risk: a systematic review and meta-analysis of cohort studies conclude:

High intakes of dairy products, milk, low-fat milk, cheese, and total, dietary, and dairy calcium, but not supplemental or nondairy calcium, may increase total prostate cancer risk. The diverging results for types of dairy products and sources of calcium suggest that other components of dairy rather than fat and calcium may increase prostate cancer risk.

These studies suggest that animal proteins found in milk increase concentrations of insulin-like growth factor I (IGF-1) which is a cancer promoting growth hormone and growth enzyme mTORC1. Those diagnosed with prostate cancer see reductions in mortality and PSA levels with plant-based diet changes and increased risks with greater dairy consumption.

Milk and dairy products may help reduce colorectal cancer risks due to the calcium binding to pro-inflammatory secondary bile acids and ionized fatty acids, though some high-fat content cheeses increase the bile acid levels and therefore the cancer risk. This video however argues studies show plant based calcium will be a better means of obtaining the same cancer risk reduction benefits.

From nutritionfacts.org, this video walks through the potential health impacts of naturally occurring estrogen in cow's milk and dairy products. Studies find increased estrogen levels from milk consumption and greater risk of endometrial cancer for post menopausal women. The final paper discussed assessed the risk of breast cancer due to milk and dairy. The paper states:

Given the lack of chronic bioassays of oral toxicity of the seven hormone compounds in the public literature and the limitations of existing residue surveillance programs, it is not currently possible to provide a quantitative characterization of risks that result from the use of hormonal drugs in food animal production, complicating our understanding of the role of dietary hormone exposure in the population burden of breast cancer.

Article with video from Dr. Aaron Carroll at Healthcare Triage arguing that the marketed benefits of milk, specifically benefits from calcium and improved bone density, are not backed by the evidence. Further milk is a calorie laden beverage and can cause GI bleeding due to excessive milk consumption. Cited is this metastudy examining calcium intake and hip fracture risks - Calcium intake and hip fracture risk in men and women: a meta-analysis of prospective cohort studies and randomized controlled trials that showed:

Pooled results from prospective cohort studies suggest that calcium intake is not significantly associated with hip fracture risk in women or men.

and a similar finding in Milk intake and risk of hip fracture in men and women: a meta-analysis of prospective cohort studies that stated:

Our conclusion is that in our meta-analysis of cohort studies, there was no overall association between milk intake and hip fracture risk in women but that more data are needed in men.

First article that popped up on google when I searched "is milk healthy". Here are the 5 summary positions proposed by this article:

1. Milk Is Packed With Nutrients "Milk contains a wide array of nutrients, including vitamins, minerals, protein, healthy fats and antioxidants. Keep in mind that its nutritional content can vary depending on many factors."

2. It’s A Good Source of Quality Protein Milk is a rich source of quality protein that contains all nine essential amino acids. It may help reduce age-related muscle loss and promote muscle repair after exercise.

3. Milk Benefits Bone Health Milk contains a variety of nutrients that benefit bone health, such as calcium, vitamin D, phosphorus and magnesium. Studies suggest that consuming milk and dairy products may prevent osteoporosis and reduce the risk of fractures.

4. Helps Prevent Weight Gain Adding milk, especially whole milk, to your diet may prevent weight gain.

5. Milk Is a Versatile Ingredient Milk is a versatile ingredient that can be added to your diet in a number of ways. Try adding it to smoothies, coffee or your morning oatmeal.

Looking through the papers cited in this article, I believe some of these summaries are overstating the conclusions or observations made in the referenced studies. Points 3 and 4 specifically rely on observational studies or studies that look at a specific component of cow's milk like calcium, instead of milk and dairy as a whole. Preventing weight gain additionally was only seen in a specific demographic (older women of normal starting weight) and only relevant for high fat dairy products. That means it was likely the milk fats that were the correlating factor instead of cow's milk.