Natural estrogens are up to 100,000 times more potent than their environmental counterparts, such as the estrogen-like compounds in pesticides.
"Among the routes of human exposure to estrogens, we are mostly concerned about cow's milk, which contains considerable amounts of female sex hormones," Ganmaa told her audience. Dairy, she added, accounts for 60 percent to 80 percent of estrogens consumed.
Part of the problem seems to be milk from modern dairy farms, where cows are milked about 300 days a year. For much of that time, the cows are pregnant. The later in pregnancy a cow is, the more hormones appear in her milk.
Milk from a cow in the late stage of pregnancy contains up to 33 times as much of a signature estrogen compound (estrone sulfate) than milk from a non-pregnant cow.
In a study of modern milk in Japan, Ganmaa found that it contained 10 times more progesterone, another hormone, than raw milk from Mongolia.