Background Current cow milk production practices introduce considerable levels of pregnancy hormones into the milk. Humans are exposed to these hormones when cow milk is consumed, and this may explain the observed association between cow milk consumption and several hormone-sensitive cancers. Objectives The aim of the study was to evaluate whether cow milk consumption is associated with an increase in urinary excretion of sex steroid hormones and their metabolites in humans. Methods We conducted a randomized crossover intervention feeding experiment. A total of 109 postmenopausal women consumed 1 L of semiskimmed milk (1.5% fat) per day for 4 d and 1 L of whole milk (3.5% fat) per day for 4 d, intersected by 4-d wash-out periods. Sex steroid hormone levels were measured in 24-h urine samples collected at the end of each intervention and wash-out period. Results Estrogens, androgens, and progesterone were detected in the examined milk samples used for our intervention. Although a very high proportion of the estrogens were conjugated, only small proportions of the androgens and progesterone were conjugated. Milk consumption resulted in a significant increase in urinary estrone (E1) excretion, whereas estradiol (E2), estriol (E3), and 16ketoE2 excretion only increased after semiskimmed milk consumption. Urinary pregnanediol glucuronide excretion was not significantly affected. Conclusion Cow milk consumption increases urinary excretion of E1 in humans. Ingestion of semiskimmed milk appears also to raise E2, E3, and 16ketoE2 excretion, but future studies need to confirm these associations. This trial was registered at https://www.drks.de as DRKS00003377.
Michels, K. B., Binder, N., Courant, F., Franke, A. A., & Osterhues, A. (2019). Urinary excretion of sex steroid hormone metabolites after consumption of cow milk: A randomized crossover intervention trial. American Journal of Clinical Nutrition, 109(2), 402–410. https://doi.org/10.1093/ajcn/nqy279