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Hormones in Meat and Dairy--Should You Be Worried?

Updated: May 18, 2022


According to a Pew Research poll, many Americans are concerned about risks associated with eating food from livestock that have been given antibiotics or hormones during growth and production. At least 32% consider meat consumption from these animals a significant health risk to healthy individuals. As both accurate and fear-based information regarding agriculture, farming, processing, and producing food becomes available via the internet; consumers continue to question the content of the foods they eat. Sustainability, animal and environmental welfare, and the impact on health are all factors that influence buying decisions.

In the 2019, Food and Health Survey from IFIC (The International Food Information Council), between 30% and 50% of consumers are more likely to buy a product because the label states it contains no added hormones or steroids, it's "natural," and that no antibiotics were used during the animal's growing process. The same survey indicated that the participants gained knowledge about food from friends and family. Inaccurate information may lead to unfounded fear and finding appropriate guidance on these matters can be challenging.

Hormones in Agriculture

Hormones are given to livestock to make production more efficient. The hormones used in beef production are estrogen, testosterone, and progesterone or their synthetic versions. Specific hormones can increase milk production and growth of the animals and usually result in more food products using fewer animals. This increase in efficiency translates into using less land, water, and animal feed. By using fewer resources and producing more with less livestock, there is a positive impact on the environment that would not be available without hormones.

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Hormones given to food animals are metabolized by their bodies quickly, and each hormone performs a specific function and communicates with a receptor individually matched to its chemical structure.

For comparison, adult men and women generally consume ten mcg progesterone per day, .1 mcg estrogen per day, and .05 mcg testosterone per day from food sources. These amounts are significantly less than human endogenous production.

A 4-ounce cut of beef from a treated animal contains about 1.6 nanograms of estrogen, while the same amount of meat from an untreated animal contains 1.2 nanograms of estrogen. These amounts are appreciably less than what is synthesized naturally in the human body.

The FDA has stated that the meat from animals treated with hormones is safe for consumption at any time. There isn't a waiting period between when the hormones are administered, the meat is sold and then consumed.

Reasons for Hormone Administration

According to the Food and Drug Administration (FDA), growth-promoting hormones have been used for more than 60 years in beef cattle and sheep. Growth hormone implants are pellets that are typically inserted into the ear of a steer (a young male cow) or heifer (a young female cow that has not given birth). They're designed to slowly release the hormone over time to ensure that the dosage remains low. The implants are not allowed by law to be used to produce pigs, dairy cows, veal calves, and poultry. These animals have other methods of improved growth and production, such as enhanced genetics and feed additives. The naturally occurring hormones are extracted from other animals. If the synthetic version is used, they are created in a lab and mimic the natural versions.

Some estimates suggest that growth promotants may increase beef production by 700 million pounds while increasing lean tissue anywhere from 8-20% within the United States beef industry. Feed efficiency is also improved while utilizing land more effectively, which may be beneficial for the environment. Feed efficiency measures animals' ability to turn the nutrients into products (milk or beef). Animal feed is formulated by a licensed veterinarian and monitored regularly.

Most male bulls are neutered when they are young and then become steers to reduce aggression, prevent aggressive animals from hurting themselves or other bulls, and make them calmer and more compliant when employees work with them. The implants cattle receive are male hormones produced by their bodies, estrogen, progesterone, and testosterone. These same hormones also cause bulls to grow faster with more substantial muscle tissue and less fat distribution. Heifers (female cattle that have never given birth to a calf) produce much less of these hormones than older or pregnant cows. Administering these hormones to younger female cattle allows them to grow more quickly.

The Food and Drug Administration is responsible for the approval or disapproval of hormone drugs given to livestock. Growth hormones are only approved for use after studies have proven their safety to the animals treated, those who consume animals treated, and the environment via feces. The information obtained through these studies and their findings are available to the public via a "Freedom of Information Summary."

There is what is referred to as a "zero-day withdrawal period" for an animal that has had hormone implants. This refers to the fact that the meat from treated animals is safe for human consumption immediately following slaughter. Unlike antibiotic treatment, there isn't a specified number of days between injection and when an animal can be sold for food. Because hormones are administered at very low doses from implants, they have been metabolized and excreted via bodily processes and are not present in tissue in amounts over the FDA-designated safe levels.

Naturally Occurring Hormones

Hormones are chemical "messengers" produced by endocrine glands that travel through the blood to various organs and tissues throughout humans and animals' bodies. They perform several functions, including reproduction, appetite regulation, growth, sexual functions, and metabolism.

Estrogen, progesterone, and testosterone are naturally occurring hormones produced in humans and animals throughout the life cycle. For non-pregnant women, the estrogen average is 5 mg/day, and adult men create approximately 10 mg/day of testosterone and androstenedione.

When the amount of hormone produced is insufficient to perform these functions, it can have health implications and cause disease. Several factors contribute to a hormone deficiency, including aging, illness, environmental, genetics, and stress.

Synthetic Hormones

The synthetic compounds used for growth promotion in beef and dairy cows are zeranol, trenbolone acetate, and melengestrol acetate . Each of these is a manufactured version of the naturally occurring hormones and is administered via an implant in an animal, usually behind the ear. The implants release the hormones into the bloodstream over a specified period. Once the animal is harvested, the ear with the implant is discarded, so there is no danger of the implant entering the food chain.

Before using synthetic versions, the hormones must undergo toxicological testing in laboratory animals to establish that they're safe for consumption. They can then be used in agriculture animals. Toxicology testing is used to determine the degree to which a substance can harm a living animal and define levels that do not cause injury or distress. Additionally, livestock producers must demonstrate that hormone levels that remain in the animal tissues are below levels deemed appropriate and safe via testing. A safe level is an amount of hormone that remains in edible tissues that have been proven to have no harmful effects on humans.

In assessing risk for hormonal implantation in a recent meta-analysis including estrogen, progesterone, testosterone, zeranol, trenbolone, and melengestrol acerate, it indicated that steroid hormones have zero impact on human health when they are used according to instructions and under acceptable veterinary practices.

Risk Factors for Using Hormones

When assessing veterinary drugs, the toxicological impact and maximum safe intake for humans are determined. The toxicological implications are defined as biologically adverse effects in humans that directly cause the drugs being administered to the food animal. These effects might include weight changes, immune system abnormalities, or any other disruption of humans' normal biological functions. In addition to physical adversities, whether or not a drug changes, the gut microflora is tested and treated with equal importance during procedural testing. The drugs are approved when proven that they will not affect human health with any of the above health complications.


The public's concern that the hormonal treatment of animals for growth and production will harm human health by increasing tumor growth in people who have cancer or will increase cancer prevalence in healthy individuals. Estrogen given to the animal will mimic estrogen already present in the human body. It's been proposed that consuming meat from animals given estrogen will increase humans' levels and promote cancer cell proliferation. After examining the research, which cites several meta-analyses, there appears to be an unsubstantial connection between consuming livestock products treated with hormones and the cancer increase The amount eaten via treated animals is substantially lower than what's produced naturally in humans. Estradiol ingested from meat would not exert hormonal effects due to its low bioavailability after passing through the gastrointestinal and hepatic systems.

In short, although many industry-funded studies on the impact of administering hormones to animals indicate there is no risk to human health, there are smaller, independent studies that show there may be a potential risk but fail to prove this. More research is needed in this area.


One area of concern is the exogenous hormones, estrogen, testosterone, progesterone, and their synthetic counterparts, ingested from an outside source and may have a disruptive endocrine effect on prepubertal adolescents. These effects include altered growth and development and sexual reproduction abnormalities. In both boys and girls, the age of puberty onset has decreased for the last 150 years.

Researchers have explored the possibility that hormone administration to food animals may be partially responsible for reducing puberty in adolescents.

Although it's been suggested that there's a correlation between consumption of hormones and early puberty, the research does not support it . In a meta-analysis of studies about this issue, the conclusion was that there was no clear indication that hormone administration to food animals leads to early puberty onslaught in adolescents.

The residual amount of hormones allowed in livestock before it is sold gets processed via human digestion when the food animal has been eaten and is not biologically active. However, some consumers and researchers would like to see more studies in this area before concluding that livestock hormones are not related to early-onset puberty. In short, more research is a need because, to date, results have been inconclusive and unable to pinpoint livestock hormones as being the cause of adverse health effects.

Several factors can influence puberty onset, including stress, high-quality nutrition in the early years, and obesity. Both obesity rates and increased availability of nutrient-dense foods have grown alongside the early beginning of puberty rates. Moreover, some studies point to a correlation between the increase in rates of obesity and growth in early puberty. However, more research is needed to be able to state this definitively.

Hormones in Dairy

Bovine Somatotropin (BST) and its synthetic version Recombinant Bovine Somatotropin (rBST) are the primary hormones used in some dairy cows for increased milk production. BST is a pituitary-derived hormone that was approved for use in 1993 by the Food and Drug Administration. However, not all dairy farmers use BST on their livestock.

Somatotropin is a naturally occurring hormone produced in the pituitary gland of animals and humans. It is responsible for and essential to maintaining health and proper growth. A cow having a normal lactation cycle continues for approximately ten months following the birth of a calf. When used, the hormone is started two months after a cow has given birth and given to the cow for the remaining eight months until the end of the lactation cycle. Although cows produce somatotropin naturally, supplementation produces 10-15% more milk on average. The increase in milk production could result in less land, resources, and water used to create the same amount of milk without supplementation. Following the ten months of lactation and milking, the cow can rest for two months until the next lactation period.

BST is a protein produced by the cow and, once ingested by people, is broken down via human digestion. Additionally, the human body does not recognize BSTproduced by cows because its structure differs from the somatotropin produced naturally by the human pituitary gland. Therefore, due to the FDA's safety testing, BST has a zero-day withdrawal because it does not impact humans. This period referred to as "the withdrawal period," is when an animal has to be separated before it can be sold and eaten. In this case, there is no specified time between treatment and consumption. In other words, meat from a treated cow can be eaten immediately.

Dairy producers that use BST and rBST in dairy cows do so because they can increase milk production substantially. In the 1970s, a biotech company patented the genes for naturally occurring BST. This made it possible to create a synthetic version and make it more readily available to dairy farmers by producing larger quantities. The new product, rBST, is a purified form of BST and is referred to as recombinant BST. Structurally, there is no difference between the two.

It is difficult to estimate how each cow will respond to treatment; however, it is suggested that milk production may increase by 15%. However, only about 9.7% of dairy farms — a relatively small amount— use BST or rBST.

JECFA, the Joint Food, and Agriculture Organization of the United Nations, World Health Organization, is an international scientific expert committee that has been meeting since 1956. Its purpose is to evaluate the safety of food additives, natural toxicants, contaminants, and veterinary drugs in food. In 2014, after 20+ years of using rBST, the 78th meeting of the Joint Food and Agriculture Organization of the United Nations, World Health Organization Expert Committee on Food Additives concluded that there were no concerns or adverse effects health with using BST/rBST. Furthermore, it stated that there had not been an increase in either type 1 or 2 diabetes in adults (due to the concern that rBST may increase IGF concentrations) and children with rBST treatment of cows, that dairy products provide essential nutrition that benefits health, and can be part of a healthful diet.

It's important to note that rBST has been banned in several countries, including Canada and the European Union. The decision to refuse was not because of the adverse effects on human health but because of the potential negative impact on animal wellbeing. Areas of concern include an increase in mastitis, a reduction in fertility, and increase foot problems for the animal. The studies are conflicting on this matter.

More efficient farming practices that include climate-controlled barns to help protect from predators, extreme weather and disease, and regulated and automated feeding systems, decrease the occurrence of these health conditions. These advances translate into the optimal and humane treatment of livestock and make it somewhat difficult to pinpoint rBST's use being the cause of specific animal disorders because they are rarer in improved farming conditions.

Hormones in Non-Dairy Livestock

Estrogen is one of the hormones used in livestock growth and occurs naturally in every human and animal. The highest amounts are found in pregnant animals. The intake of estrogen from treated animals is 40-1,000 times lower than the value produced daily by the human body.

Progesterone is also used as a growth promoter in meat animals. It's identical to that produced by both animals and humans. When ingested from treated livestock , it's poorly absorbed and rendered inactive in the gastrointestinal tract and liver. A veterinarian administers progesterone according to directions; it does not have negative health implications for humans.

In an animal study of progesterone concentrations in edible tissues of treated and untreated calves, veal, heifers, and steer, the only difference in progesterone levels was found in the adipose tissue. The treated animals had levels that were several times higher than the non-treated livestock. Although the levels were more elevated, they were still approximately one thousand times below the level produced daily in both men and women in good health.

In one study, 100 micrograms of progesterone were given subcutaneously to mice and were found to increase the incidence of mammary, ovarian, or uterine tumor growth. However, the IARC determined that there was little evidence to suggest carcinogenicity in humans.

In the three synthetic varieties of hormones that may be used, zeranol, melengestrol and trenbolone, acceptable daily intake (ADI) and maximum residue limit (MRL) have been established for each substance. When used according to these guidelines, they do not pose a threat to human health.

Plant Hormones

The hormones that plants naturally produce are referred to as phytoestrogens. They are structurally comparable to human estrogen. There are several different types of plant hormones, but chemically they may share some similarities in structure to animal hormones. For this reason, the biological effects of plant hormones may be identical to some animal hormones. However, as it does animal hormones, the human digestive system breaks d own plant hormones.

There's been some concern over whether the phytoestrogens found in foods such as soy may have an estrogenic effect on humans. Because of the widespread use of products that contain phytoestrogens, mainly soy products, the amount of consumption varies and is difficult to assess due to inconsistencies in food recalls and reporting. Soy contains isoflavones which mimic estrogen. Since some breast cancers utilize estrogen to grow, there is some concern that soy consumption may contribute to cancer proliferation. Evidence of adverse effects is inconclusive and does not determine that soy consumption contributes to cancer occurrence.

One meta-analysis, which included 40 randomized controlled trials, 11 uncontrolled trials, and 80 observational studies, looked at the potential effects of soy and isoflavone intake on breast cancer incidence and recurrence. It concluded that soy consumption might be associated with a reduced risk of breast cancer incidence, reproduction, and mortality.

It appears that moderate intake of phytoestrogens from food sources and not supplements are beneficial for health. One to two servings of whole soy foods (tofu, soy milk, edamame, or soy nuts) providing 7 grams of protein and 25 milligrams of isoflavones per serving is considered a moderate amount consumption.

It also seems that there are little to no adverse effects of phytoestrogen on hormonal function when eaten in moderate amounts.


Insulin growth factor (IGF-1) is a hormone found naturally in the body and is similar to insulin. One concern with using rBST in cows is its potential to increase IGF-1 level in the blood and increase incidences of certain types of cancer; however, there are vital factors to consider. Somatotropin is created by the pituitary gland and is partly responsible for growth and cell duplication. This raises the possibility that it may contribute to an increase in cancer cell proliferation. One meta-analysis of IGF-1 and IGFBP-3 and cancer risk demonstrated a small correlation between these two hormones and certain cancers.

Some studies have indicated that blood levels of IGF-1 and the development of prostate, breast, colon, and other cancers are related. However, these studies' conclusions have not indicated that IGF-1 levels increased from drinking treated cow milk, and it has not been determined that rBST has been the cause of elevated cancer risk.

Additionally, The American Cancer Society has summarized these points based on their independent findings:

· Neither natural nor synthetic BST has been found to affect human growth hormone receptors

· Concentrations of IGF-1 are slightly higher in cows treated with rBST compared to untreated cows. However, it's below the normal range of IGF-1 levels that occur naturally.

· IGF-1 is inactivated by pasteurization;

· It has not been determined precisely how much intact IGF-1 is absorbed upon ingestion.

· By one study's estimation, if the amount of IGF-1 in milk from treated cows were completely absorbed without any degradation, it would be approximately .09% of the average level of IGF-1 produced naturally by the human body. The average levels of IGF-1 are between 200-400 ng/ml. 55

Food Labeling

In one shopping survey done by Consumers Union, there were more than twenty different claims made on various meat packages, leading to confusion for consumers. If the product label states "no antibiotic residue," it does not necessarily mean an animal was raised without antibiotics. It may merely indicate that the animal had been taken off antibiotics for a period before selling it for consumption. Health professionals should be familiar with the labeling parameters to educate consumers effectively.

According to the United States Department of Agriculture (USDA), if poultry or pork labels have the words "No Hormones Added or Administered," it must be followed by a statement that indicates "Federal Regulations Prohibit the Use of Hormones." Neither of these two meat products is allowed by law to be bred using growth-promoting hormones. Due to improved breeding, nutrition, living conditions, and overall bird health, hormones are not needed to increase chickens' growth. They have naturally grown in size over time. Also, there are no commercially available growth hormones for chickens, and it would be costly to use these hormones in the large chicken population.

In pork products, living conditions, farming practices, and better nutrition have contributed to a naturally healthier animal. They have eliminated the need for the use of growth-promoting hormones when raising pigs. Therefore, the addition of these words on the label is more of a marketing ploy.

Beef labels ay indicate "no hormones administered" if there is documentation provided to the USDA Food Safety Inspection Service, meaning that the producer did not administer hormones at any time during the raising of the animals.

According to the United States Department of Agriculture, bison is not allowed to be raised with the use of antibiotics or hormones. Bison are generally given a custom diet and slaughtered at approximately 18 months of age. The meat is tender and similar to beef in both nutrient content and consistency. However, beef is higher in fat and calories.

Additionally, all meat that carries the label "certified organic" by the USDA has been raised without antibiotics or hormones to increase growth.

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