A large observational cohort study^[1] in Sweden found that women consuming more than 3 glasses of milk a day had almost twice the mortality over 20 years compared to those women consuming less than one glass a day. In addition, the high milk-drinkers did not have improved bone health. In fact, they had more fractures, particularly hip fractures.

Interestingly, the study also found that fermented milk products (cheese and yogurt) significantly decreased mortality and fractures among these women. For each serving of these fermented dairy products, the rate of mortality and hip fractures was reduced by 10-15%. The researchers pin the negative effects of liquid milk on D-galactose, a breakdown product of lactose that has been shown to be pro-inflammatory. Milk has much more D-galactose than does cheese or yogurt.

I am surprised that this study garnered so much mass media attention upon its release, as it highlights the deleterious side of milk, but I also think it is important to keep the findings in context. And when it comes to the health effects of dairy, the context is not so pretty:

1. In observational studies both across countries and within single populations, higher dairy intake has been linked to increased risk of prostate cancer ^[2].
2. Observational cohort studies have shown higher dairy intake is linked to higher ovarian cancer risk^[2].
3. Cow’s milk protein may play a role in triggering type 1 diabetes through a process called molecular mimicry^[3].
4. Across countries, populations that consume more dairy have higher rates of multiple sclerosis^[4].
5. In interventional animal experiments and human studies, dairy protein has been shown to increase IGF-1 (Insulin-like Growth Factor-1) levels. Increased levels of IGF-1 has now been implicated in several cancers^[5].
6. In interventional animal experiments^[6] and human experiments^[7], dairy protein has been shown to promote increased cholesterol levels (in the human studies and animal studies) and atherosclerosis (in the animal studies).
7. The primary milk protein (casein) promotes cancer initiated by a carcinogen in experimental animal studies^[8].
8. D-galactose has been found to be pro-inflammatory and actually is given to create animal models of aging^[1].
9. Higher milk intake is linked to acne^[9].
10. Milk intake has been implicated in constipation^[10] and ear infections ^[2].
11. Milk is perhaps the most common self-reported food allergen in the world^[11].
12. Much of the world’s population cannot adequately digest milk due to lactose intolerance.

So despite being very pleased that the public is glimpsing some of the evidence against milk in this recent study (though they also could be hearing about the benefits of cheese and yogurt from this same study), I think there is a far more powerful story; a story that takes into account the largely hidden context of diet and dairy research. There is a wealth of indirect evidence of very serious possible harms of consuming dairy foods, and, on the flip side, the evidence that milk prevents fractures is scant.

As we look beyond the headlines, it is hard to think that we should continue to consume the lactation fluid that exists in nature to nourish and rapidly grow calves.

References

1. Michaelsson K, Wolk A, Langenskiold S, et al. Milk intake and risk of mortality and fractures in women and men: cohort studies. Bmj 2014;349:g6015.
2. Lanou AJ. Should dairy be recommended as part of a healthy vegetarian diet? Counterpoint. The American journal of clinical nutrition 2009;89:1638S-42S.
3. Dahl-Jorgensen K, Joner G, Hanssen KF. Relationship between cows’ milk consumption and incidence of IDDM in childhood. Diabetes Care 1991;14:1081-3.
4. Malosse D, Perron H, Sasco A, Seigneurin JM. Correlation between milk and dairy product consumption and multiple sclerosis prevalence: a worldwide study. Neuroepidemiology 1992;11:304-12.
5. Key TJ. Diet, insulin-like growth factor-1 and cancer risk. Proc Nutr Soc 2011:1-4.
6. Kritchevsky D. Dietary protein, cholesterol and atherosclerosis: a review of the early history. The Journal of nutrition 1995;125:589S-93S.
7. Gardner CD, Messina M, Kiazand A, Morris JL, Franke AA. Effect of two types of soy milk and dairy milk on plasma lipids in hypercholesterolemic adults: a randomized trial. Journal of the American College of Nutrition 2007;26:669-77.
8. Youngman LD, Campbell TC. Inhibition of aflatoxin B1-induced gamma-glutamyltranspeptidase positive (GGT+) hepatic preneoplastic foci and tumors by low protein diets: evidence that altered GGT+ foci indicate neoplastic potential. Carcinogenesis 1992;13:1607-13.
9. Spencer EH, Ferdowsian HR, Barnard ND. Diet and acne: a review of the evidence. Int J Dermatol 2009;48:339-47.
10. Caffarelli C, Baldi F, Bendandi B, Calzone L, Marani M, Pasquinelli P. Cow’s milk protein allergy in children: a practical guide. Italian journal of pediatrics 2010;36:5.
11. Rona RJ, Keil T, Summers C, et al. The prevalence of food allergy: a meta-analysis. J Allergy Clin Immunol 2007;120:638-46.