The Hidden Risk of Soy and Caffeine

By Susan Goldhaber MPH — Mar 14, 2023
I was struck by this large heading on an EPA website, “Rebuilding the Endocrine Disruptor Screening Program.” This program does not need to be rebuilt; it should be eliminated and consolidated with existing programs within the EPA.
Image by Pexels from Pixabay

Endocrine disruptors are substances that interfere with or alter hormones, which are part of the endocrine system. Most attention focuses on chemicals, particularly pesticides, that cause these effects, i.e., “endocrine disrupting chemicals.” The purpose of EPA’s Endocrine Disruptor Screening Program is to determine which chemicals cause these effects and then to ban or severely limit their use.

Endocrine disruption is an important issue, but there is a fundamental flaw in the Endocrine Disruptor Screening Program. There is no yes-no answer as to whether a chemical is an endocrine disruptor. The issue is much more complicated and includes substances other than the chemicals evaluated by EPA.

EPA’s Endocrine Disruptor Screening Program

The EPA’s Endocrine Disruptor Screening Program was established in 1998 under the Federal Food, Drug, and Cosmetic Act, which directed the EPA

“to develop a screening program …. to determine whether certain substances may have an effect in humans that is similar to an effect produced by a naturally occurring estrogen, or such other endocrine effect as the Administrator may designate.”

In 2008, EPA selected a battery of animal tests for Tier-1 screening to identify chemicals potentially affecting estrogen, androgen, or thyroid hormones. EPA issues test orders to chemical manufacturers requiring that they carry out this battery of animal tests on select chemicals. The rebuilding of the Endocrine Disruptor Screening Program allows two non-animal tests to be used as alternatives to four animal tests in first-tier screening in the program.    

I applaud EPA for allowing the use of non-animal tests as alternatives to animal tests; this is a long overdue step, as I have previously written.

EPA estimates that it costs industry about $1 million per chemical and can take up to six years to complete the first-tier battery of tests. Out of approximately 3,700 pesticide-active and inert ingredients, the EPA has only finalized orders for first-tier screening for 52 chemicals and has not completed any secondary, additional testing based on first-tier results. This answers the question as to why EPA is rebuilding the Endocrine Disruptor Screening Program.

Endocrine Disrupting Substances

What drove the concerns that led to the establishment of the Endocrine Disruptor Screening Program were reports beginning in the 1990s about frogs and fish exhibiting abnormal sexual differentiation, including the feminization of male fish. Similar effects were observed in some invertebrates (mussels), reptiles (alligators), and birds.

Numerous studies have confirmed these effects in wildlife and laboratory animals; however, the results in humans are less clear-cut. Some studies in humans have suggested an association between endocrine-disrupting chemicals and reduced sperm counts and quality, early menopause, decrease in testosterone levels, and other reproductive disorders. However, the evidence is inconclusive, particularly regarding the levels of chemicals needed to cause these effects.

If you look at a list of endocrine-disrupting chemicals, the list will probably include:

  • Atrazine
  • Bisphenol A (BPA)
  • Dioxins
  • Perchlorate
  • Phthalates
  • Perfluoroalkyl and Polyfluoroalkyl Substances (PFAS)
  • Polybrominated diphenyl ethers (PBDEs)
  • Polychlorinated biphenyls (PCBs)
  • Triclosan

Naturally Occurring Substances – Phytoestrogens, metalloestrogens, caffeine

The elephant in the room is that these lists do not include naturally occurring substances that are endocrine disruptors.

This is not just a minor omission; many naturally occurring substances have demonstrated endocrine effects in humans but are rarely mentioned by government agencies, such as the EPA.     

Phytoestrogens are naturally occurring substances in plants, such as genistein, daidzein, and coumestrol, that are in soy products, including tofu and soy milk, and alfalfa. In the 1940s, there were reports that sheep grazing on clover-rich pastures in Australia exhibited infertility, miscarriages, and reproductive abnormalities in their offspring. Phytoestrogens in the clover were responsible. Today’s farmers use various agricultural methods to lower grazing mammals' consumption of phytoestrogens.

Soy has been known to be an endocrine disruptor for decades. Both genistein and daidzein block the synthesis of thyroid hormones, which is why iodine is added to soy infant formula and other soy-rich foods. Soy also decreases the absorption of synthetic thyroid hormone, which is why additional iodine intake is advised for patients at risk for hypothyroidism (underactive thyroid) if they consume soy as part of their regular diet.

Studies also show reproductive effects in women from consuming high levels of soy. A meta-analysis concluded that high soy intake increases menstrual cycle length and suppresses some hormones. Studies have reported effects including uterine bleeding and suppression of the menstrual cycle from high soy intake.            

Natural inorganic trace elements found in soil, metalloestrogens such as cadmium, may also act as endocrine disruptors. Several studies have pointed to diverse biological contaminants, including metalloestrogens, that may be responsible for the endocrine-disrupting effects seen in frogs and other wildlife.

Caffeine is the most crucial compound left off almost all lists of endocrine disruptors. Caffeine consumption causes the body to produce extra cortisol (a steroid hormone), which changes estrogen levels. A study showed that consumption of 200 milligrams of caffeine per day (about 2 cups of coffee) resulted in increased or decreased estrogen levels, depending on the ethnicity of the subjects.  

Most doctors today advise severely limiting caffeine intake during pregnancy. This is because low levels of caffeine effects fetal stress hormones and caffeine has been associated with a range of adverse effects on the fetus, even at doses previously considered safe (200 milligrams or 2 cups of coffee per day).

 A Fresh Look at Endocrine Disruption

Endocrine disruption needs to be examined in a much broader context than is currently being done. What is needed is a real focus on education and transparency in informing the public about the nature of endocrine disruption and the major substances causing these effects. 

For example, environmental and consumer groups urge people to rigidly avoid bisphenol A (BPA) or phthalates in consumer products but do not mention the much more significant risk from the caffeine in coffee or other beverages. 

The ultimate absurdity is that many people believe their risk of endocrine-disrupting effects is more significant from the BPA in the cups rather than the actual coffee content. Whenever I see someone drinking multiple cups of coffee, proudly displaying a BPA-free cup, I realize that we continue to fail the public when we don’t include naturally occurring substances on the list of endocrine disruptors.  

So many health-conscious Americans believe that soy products are the ultimate in healthy eating. However, as discussed in this article, an abundance of animal data unequivocally demonstrates that soy, at relatively low doses, can permanently alter the structure and function of the endocrine system. The scientific establishment and government agencies ignore the effects of soy on the endocrine system, including its impact on infants fed soy formula. All the attention and money are spent on compounds such as BPA and phthalates, which have less potency and lower exposure than soy.

One clear recommendation is for Federal agencies to

“Develop dietary guidelines that consider the endocrine-disrupting properties of soy and other hormonally active foods, particularly for vulnerable groups such as pregnant women and hypothyroid individuals.” - Endocrine disruption by dietary phyto-oestrogens

The Endocrine Disruptors Screening program does not consider the dose of a chemical that causes the endocrine effects. Since the dose makes the poison, having a program that uses Yes-No tests to decide if a chemical should be labeled as an endocrine disruptor is meaningless.

The important consideration should be whether the chemical disrupts hormones at levels commonly found in the environment, presenting a risk to humans or wildlife, a concern that the Endocrine Disruptors Screening Program does not address.   

There is no need to invent new programs; programs already address this issue.

  • The primary pesticide law, Federal Insecticide, Fungicide, and Rodenticide Act (FIFRA), requires EPA to develop detailed risk assessments of the potential for the pesticide to harm humans, wildlife, fish, and plants and the levels at which it causes this harm before it is registered for use in the U.S.
  • EPA considers the effect of the pesticide on every organ system and tissue, including the endocrine system. There is no need for an additional screening program; a complete review of each pesticide is performed every 15 years.     

A yes-no battery of screening tests does nothing to further the understanding of endocrine disruptors. The EPA should recommend to Congress to consolidate this program under existing pesticide programs, where it better belongs. This would save millions of dollars and free up resources to be better directed to programs addressing more relevant high-risk issues.