Should We Avoid Dairy? Milk & Health: The Evidence
IGF-1 is insulin-like growth factor-1. Cows have been bred to produce more IGF-1, plus they are treated with hormones. Cow’s milk contains IGF-1, and blood levels may be higher in milk drinkers. PubMed lists numerous studies suggesting an association of higher blood levels of IGF-1 with various cancers, but the evidence doesn’t show that milk drinkers are actually more likely to develop those cancers. (IGF-1 is produced in the human liver in considerably larger amounts than anyone is likely to get from dairy foods.)
An article on Healthline says, “IGF-1 has been linked with an increased risk of prostate cancer.”
A new study published in February 2020 in the International Journal of Epidemiology found an association between high dairy intake and breast cancer - women who drank the most cow’s milk per day had 50% increased risk for breast cancer compared with women who drank the least.
“New Study Suggests Milk Could Increase Breast Cancer Risk” - using data from the long-running Seventh Day Adventists study ... “provocative, but not enough to warrant a change in guidelines”.
Conclusion: I’m not convinced. The observational studies looking for a correlation between cancer and consumption of dairy foods are far from definitive. While there is legitimate concern about IGF-1, the evidence has not shown that fear of cancer is a good reason to avoid consuming dairy products.
In an excellent review MILK & HEALTH in The New England Journal of Medicine, two scientists from Harvard (Walter Willett MD, DPH and David Ludwig MD, PhD) help set the record straight (bolstered by 121 references). They point out that cows have been bred to produce more insulin-like growth factor, and there are increased levels of hormones in their milk.
Did you think babies need milk? They don’t. They can get adequate nutrition for growth and development without it, as long as there is careful attention to diet and vitamin intake. Milk consumption increases their attained height - tall stature is associated with lower risk of cardiovascular disease but higher risks of many cancers, hip fractures, and pulmonary emboli.
Calcium and the risk of bone fractures - the US recommendations for milk consumption were based on small studies (other countries recommend lower levels). Countries with high milk and calcium intake actually have the highest rates of hip fracture ... men’s risk of hip fracture increased by 9% for every additional glass of milk consumed during adolescence.
Strokes/coronary heart disease - dairy is lower risk than red meats but higher risk than fish. Dairy fat increases cardiovascular risk more than polyunsaturated or vegetable fat.
Diabetes risk - dairy is lower than sugary beverages, but higher than coffee.
Cancer - milk consumption may increase the risk of prostate & endometrial cancers, but may reduce the risk of colorectal cancers.
Allergies & intolerance - 4% of infants are allergic to cow’s milk, and reports suggest milk consumption may predispose to allergic disease and eczema. In adults, milk may exacerbate asthma. And lactose intolerance limits milk consumption worldwide.
Total mortality - lower mortality than processed red meat and eggs, but higher mortality than plant-based sources of protein.
Environmental effects - limiting milk production could reduce greenhouse gases and climate change, improve water use and reduce pollution, and reduce the risk of antibiotic resistance.
Conclusion - No simple answers. Milk doesn’t “build strong bones” but may actually increase the risk of fracture. There’s no evidence that reduced-fat milk has any health advantages over whole milk.
The conclusions reached in both of these articles are pretty eye-opening, and the author seems to have written to the specific skeptic SBM audience, who must clearly enjoy their meat & dairy.
The actual health benefits of dairy consumption detailed here are scant, so there is little reason for us to continue consuming dairy products, and every reason to limit and preferably stop all dairy consumption.