Hormones in Milk: Should I be Concerned About Potential Risks?

While all cow’s milk, from organic to conventional, contains tiny amounts of naturally occurring hormones, the current evidence shows that milk is safe.

Most living things, including plant and animal foods such as legumes, grains, milk, meat and eggs, contain hormones, which can be thought of as messengers that help regulate specific functions in plants, animals and people. Hormones are important to life.

Many hormones are proteins, so when they’re eaten as a part of foods, enzymes in the gastrointestinal tract digest them, which stops their biological activity in the body. Therefore, naturally occurring hormones in milk are not a health concern. No hormones are added to milk.

One naturally occurring protein hormone in milk – bovine somatotropin (bST) – is present in cows and helps to regulate normal growth and development. Although bST is found at a very low concentration in cow’s milk, this hormone is only active in cows and is not recognized by the human body. The Food and Drug Administration approved the use of the synthetic version of this protein, called recombinant bovine somatotropin (rbST), that some dairy farmers use to increase milk production.

The synthetic hormone helps cows produce milk more efficiently by using fewer environmental resources, such as feed and cropland. According to scientific experts, giving rbST to cows does not meaningfully alter the composition or nutritional quality of their milk. In fact, during the 20 years that rBST has been used, it also has been heavily researched by organizations like the National Institute of Health, the World Health Organization, the American Medical Association and Cornell University. They all corroborate the U.S. Food and Drug Administration's affirmation and reaffirmation that milk from cows treated with rBST is just as safe and wholesome as the milk we've enjoyed for generations. Put plainly, milk from cows treated with hormones doesn't have any effect on humans.

Effects of Milk Containing Estrogen

According to the research from the NIH, convential milk contains naturally occurring estrogens, primarily in the form of estrone and estradiol, because it is produced by lactating cows. The level of these hormones is higher in milk from pregnant cows, which is common in modern dairy farming. However, studies suggest the amount of estrogen in milk is relatively low compared to endogenous hormone production in humans and its impact on overall hormone balance is considered minimal in most cases. 

One Study highlights concerns abou the potential endocrine-disrupting effects of prolonged exposure to milk-derived estrogens, particularly in individuals with high dairy intake. Meanwhile, research from the NIH suggests that the digestion and metabolism of these hormones may reduce their bioavailability, limiting their physiological effects. While some observational studies have explored potential links between diary intake and hormone-related conditions, the current evidence does not conclusively show that milk consumption significantly alters estrogen levels or increase the risk of hormone-dependent diseases. 

Does Milk Cause Early Puberty?

Speculation in the early '90s that hormones in milk might be the cause of early puberty in children has led to misconceptions about milk that current science does not support. In fact, there is no conclusive evidence that drinking milk or eating other dairy foods (or any particular food!) is associated with early puberty. A large prospective study found that regular milk consumption was not related to age of menarche in girls nine or older. Some researchers hypothesize that higher rates of childhood obesity may be linked to earlier maturation in girls. On average, children are heavier today than they were in the 1970s. Excess body fat is one factor that can influence various aspects of maturation, including the timing of puberty. 

The normal onset of puberty among children can vary as much as four to five years, so there's no set timetable. The average age for girls to begin puberty is between ages 8 and 13 and for boys it's between ages 9 and 14. Early puberty is when a child's body begins maturing much sooner than normal, usually before age 8 in girls and 9 in boys. 

Early puberty can be sign of a malfunction of endocrine glands in the brain or an underlying medical problem. So, if it occurs, it's important to seek medical advice from a physician. In many cases (especially in girls) the exact cause of early puberty cannot be identified. However, race/ethnicity, being obese (which has more that tripled since the 1960s) or exposure to certain chemicals may contribute to altering hormone levels in some cases, although more research is needed. 

Parents can best help their children and teens by making sure they get balanced nutrition every day, enjoy regular phsyical activity and maintain a healthy weight. We can feel good knowing that dairy foods play a major role in helping children and teens get the nutrition they need to help support growth and development. The dairy food group contributes calcium, potassium and vitamin D to the American diet: three of the four nutrients of public health concern that children don't get enough of. Calcium and physical activity are especially important as children reach their peak bone building years in adolescence. 

Dairy companies have responded to consumer requests for choices in the dairy aisle and many now offer milk made from cows not supplemented with rBST. This business decision is based on meeting a demand in the marketplace and not related to any health or safety issue. No matter which milk you select from the grocery store shelf and put into your cart, you can feel confident that it's wholesome, safe and nutritious.